Plasmodium is a genus of parasitic
protistProtists , are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista but this group is no longer recognized in modern taxonomy...
s. Infection by these organisms is known as
malariaMalaria is a vector-borne infectious disease caused by a eukaryotic protist of the genus Plasmodium. It is widespread in tropical and subtropical regions, including parts of the Americas, Asia, and Africa. Each year, there are approximately 350–500 million cases of malaria, killing between one and...
. The
genusIn biology, a genus is a taxonomic unit used in the classification of living and fossil organisms. The term comes from Latin genus "descent, family, type, gender" , cognate with – genos, "race, stock, kin" ..In addition, genus is a taxonomic rank in the hierarchy In biology, a genus (plural:...
Plasmodium was discovered in 1885 by
MarchiafavaEttore Marchiafava was an Italian physician and zoologist who worked on malariaEttore Marchiafava , was the personal doctor of three popes and the Royal House of Savoy, a senator and professor of Pathological Anatomy at the Sapienza University of Rome...
and
CelliAngelo Celli was an Italian physician and zoologist who studied malaria.Celli graduated in medicine in 1878 at the Sapienza University of Rome, where he became hygiene professor. In 1880 with Ettore Marchiafava he studied a new protozoan discovered by Alphonse Laveran and which they called...
. Currently over 200 species of this genus are recognized and new species continue to be described.
Of the over 200 known species of
Plasmodium, at least 10 species infect humans. Other species infect animals, including
monkeyA monkey is any cercopithecoid or platyrrhine primate. All primates that are not prosimians or apes are monkeys. The 264 known extant monkey species represent two of the three groupings of simian primates...
s,
rodentRodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s,
birdBirds are winged, bipedal, endothermic , vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the Bee Hummingbird to the ...
s, and
reptileReptiles, or members of the class Reptilia, are air-breathing, generally "cold-blooded" amniotes that generally have skin covered in scales or scutes. They are tetrapods and lay amniote eggs, whose embryos are surrounded by the amnion membrane...
s. The parasite always has two hosts in its
life cycleA life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
: a
mosquitoMosquito is a common insect in the family Culicidae...
vector and a
vertebrateVertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. About 58,000 species of vertebrates have been described. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes, bony...
host.
, the genus is in need of reorganization as it has been shown that parasites belonging to the genera
HaemoproteusHaemoproteus is a genus of protozoa that are parasitic in birds, reptiles and amphibians. The genus created was by Kruse in 1890. Its name is derived from Greek: Haima - blood and Proteus - a sea god who had the power of assuming different shapes...
and
Hepatocystis appear to be closely related to
Plasmodium. It is likely that other species such as
Haemoproteus meleagridis will be included in this genus once it is revised.
History
The organism itself was first seen by
LaveranCharles Louis Alphonse Laveran was a French physician.In 1880, while working in the military hospital in Constantine, Algeria, he discovered that the cause of malaria is a protozoan, after observing the parasites in a blood smear taken from a patient who had just died of malaria...
on November 6, 1880 at a military hospital in
Constantine, AlgeriaConstantine is the capital of Constantine Province in north-eastern Algeria. Slightly inland, it is about 80 kilometers from the Mediterranean coast....
, when he discovered a microgametocyte exflagellating. In 1885, similar organisms were discovered within the blood of birds in Russia. There was brief speculation that birds might be involved in the transmission of malaria; in 1894
Patrick MansonSir Patrick Manson was a Scottish physician who made important discoveries in parasitology and was the founder of the tropical medicine field....
hypothesized that
mosquitoMosquito is a common insect in the family Culicidae...
es could transmit malaria. This hypothesis was independently confirmed by the Italian physician
Giovanni Battista GrassiGiovanni Battista Grassi was an Italian zoologist, known for work demonstrating that mosquitos carry the malaria plasmodium in their digestive tract, on the embryological development of honey bees, on parasites, particularly the vine parasite phylloxera, migrations and metamorphosis in eels, and...
working in Italy and the British physician
Ronald RossSir Ronald Ross KCB was a British physician.-Early life:Ross was born in Almora, India. He was the eldest son of General Sir Campbell Claye Grant Ross of the Indian Army and Matilda Charlotte Elderton. His grandfather was Lieutenant Colonel Hugh Ross.At the age of eight, Ross was sent to England...
working in India, both in 1898. Ross demonstrated the existence of
Plasmodium in the wall of the
midgutThe midgut is the portion of the embryo from which most of the intestines are derived. After it bends around the superior mesenteric artery, it is called the "midgut loop"...
and salivary glands of a
CulexCulex is a genus of mosquito, and is important in that several species serve as vectors of important diseases, such as West Nile virus, filariasis, Japanese encephalitis, St...
mosquito using bird species as the vertebrate host. For this discovery he won the
Nobel PrizeThe Nobel Prize is a Sweden-based international monetary prize. The award was established by the 1895 will and estate of Swedish chemist and inventor Alfred Nobel. It was first awarded in Physics, Chemistry, Physiology or Medicine, Literature, and Peace in 1901...
in 1902. Grassi showed that human malaria could only be transmitted by
AnophelesAnopheles, , is a genus of mosquito. There are approximately 460 recognised species: while over 100 can transmit human malaria, only 30-40 commonly transmit parasites of the genus Plasmodium that cause malaria which affects humans in endemic areas...
mosquitoes. It is worth noting, however, that for some species the vector may not be a mosquito.
Grassi also proposed in 1900 the existence of an exoerythrocytic stage in the life cycle: this was later confirmed by Short, Garnham, Covell and Shute (in 1948) who found
Plasmodium vivaxPlasmodium vivax is a protozoal parasite and a human pathogen. The most frequent and widely distributed cause of recurring malaria, P. vivax is one of four species of malarial parasite that commonly infect humans. It is less virulent than Plasmodium falciparum, which is the deadliest of the four,...
in the human liver.
Life cycle
Mosquitoes of the genera
CulexCulex is a genus of mosquito, and is important in that several species serve as vectors of important diseases, such as West Nile virus, filariasis, Japanese encephalitis, St...
,
AnophelesAnopheles, , is a genus of mosquito. There are approximately 460 recognised species: while over 100 can transmit human malaria, only 30-40 commonly transmit parasites of the genus Plasmodium that cause malaria which affects humans in endemic areas...
,
Culiceta,
Mansonia and
AedesAedes is a genus of mosquito originally found in tropical and subtropical zones, but has spread by human activity to all continents excluding Antarctica. Several of the species transmit important human diseases and one species, Aedes albopictus, is the most invasive mosquito in the world...
may act as vectors. The currently known vectors (more than 100 species) for human malaria all belong to the genus
Anopheles. Bird malaria is commonly carried by species belonging to the genus
Culex. The life cycle of
Plasmodium was discovered by Ross who worked with species from the genus
Culex.
Only female mosquitoes bite. Both sexes live on nectar and blood; however, one or more blood meals is needed by the female for oogenesis (egg production) as the nectar's protein content alone is insufficient.
The life cycle of
Plasmodium is complex.
SporozoiteIn the life-cycle of apicomplexan protozoa, sporozoites are cells that infect new hosts. In the parasites that cause malaria , for instance, the sporozoites are cells that develop in the mosquito's salivary glands, leave the mosquito during a blood meal, and enter the liver where they multiply...
s from the saliva of a biting female mosquito are transmitted to either the blood or the lymphatic system of the recipient. The sporozoites then migrate to the
liverThe liver is a vital organ present in vertebrates and some other animals; it has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
and invade
hepatocyteHepatocytes make up 70-80% of the cytoplasmic mass of the liver.These cells are involved in protein synthesis, protein storage and transformation of carbohydrates, synthesis of cholesterol, bile salts and phospholipids, and detoxification, modification and excretion of exogenous and endogenous...
s. The parasite matures in the hepatocyte to a schizont containing many merozoites in it. In some
Plasmodium species, the parasite in the hepatocyte would not achieve maturation to a schizont but remain as a latent or dormant form and called a hypnozoite..
The development from the hepatic stages to the erythrocytic stages has, until very recently, been obscure. In 2006 it was shown that the parasite buds off the hepatocytes in merosomes containing hundreds or thousands of merozoites. These merosomes lodge in the pulmonary capilaries and slowly disintegrate there over 48–72 hours releasing merozoites.
Erythrocyte invasion is enhanced when blood flow is slow and the cells are tightly packed: both of these conditions are found in the alveolar capilaries.
Within the erythrocytes the merozoite grow first to a ring-shaped form and then to a larger
trophozoiteA trophozoite is the activated, feeding stage in the life cycle of protozoan parasites such as the malaria-causing Plasmodium falciparum ....
form. In the schizont stage, the parasite divides several times to produce new merozoites, which leave the red blood cells and travel within the bloodstream to invade new red blood cells. The parasite feeds by ingesting haemoglobin and other materials from red blood cells and serum. The feeding process damages the erythrocytes. Details of this process have not been studied in species other than
Plasmodium falciparumPlasmodium falciparum is a protozoan parasite, one of the species of Plasmodium that cause malaria in humans. It is transmitted by the female...
so generalizations may be premature at this time.
Invasion of erythrocyte precursors has only recently been studied. The earliest stage susceptible to infection were the orthoblasts - the stage immediately preceding the
reticulocyteReticulocytes are immature red blood cells, typically composing about 1% of the red cells in the human body.Reticulocytes develop and mature in the red bone marrow and then circulate for about a day in the blood stream before developing into mature red blood cells. Like mature red blood cells,...
stage which in turn is the immediate precursor to the mature erythrocyte.
At the molecular level a set of enzymes known as
plasmepsinPlasmepsins are a class of at least 10 enzymes produced by the plasmodium parasite.There are ten different isoforms of these proteins and ten genescoding them respectively in plasmodium falciparum Plasmepsins are a class of at least 10 enzymes produced by the plasmodium parasite.There are ten...
s which are
aspartic acid proteasesA protease breaks down proteins. A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein...
are used to degrade
hemoglobinHemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of vertebrates, and the tissues of some invertebrates....
. The parasite digests 70-80% of the erythrocyte's haemoglobin but utilizes only ~15% in
de novo protein synthesis. Intraerythrocytic
Plasmodium falciparum utilizes only a fraction of the amino acids derived from the digestion of host cell cytosol for the biosynthesis of its proteins. The excess amino acids are exported from the infected erythrocyte by new transport pathways created by the parasite. The reason proposed for this apparently excessive digestion of haemoglobin is the colloid-osmotic hypothesis which suggests that the digestion of haemoglobin increases the osmotic pressure within the infected erythrocyte leading to its premature rupture and subsequent death of the parasite. To avoid this fate much of the haemoglobin is digested and exported from the erythrocyte. This hypothesis has been experimentally confirmed.
Most merozoites continue this replicative cycle but some merozoites differentiate into male or female sexual forms (
gametocyteA gametocyte is a eukaryotic germ cell that divides by mitosis into other gametocytes or by meiosis into gametids during gametogenesis. Male gametocytes are called spermatocytes, and female gametocytes are called oocytes....
s) (also in the blood), which are taken up by the female mosquito.
In the mosquito's midgut, the
gametocyteA gametocyte is a eukaryotic germ cell that divides by mitosis into other gametocytes or by meiosis into gametids during gametogenesis. Male gametocytes are called spermatocytes, and female gametocytes are called oocytes....
s develop into
gameteA gamete is a cell that fuses with another gamete during fertilization in organisms that reproduce sexually...
s and fertilize each other, forming motile
zygoteA zygote , or zygocyte, is the initial cell formed when a new organism is produced by means of sexual reproduction. A zygote is synthesized from the union of two gametes, and constitutes the first stage in a unique organism's development...
s called ookinetes. The ookinetes penetrate and escape the midgut, then embed themselves onto the exterior of the gut membrane. Here they divide many times to produce large numbers of tiny elongated
sporozoiteIn the life-cycle of apicomplexan protozoa, sporozoites are cells that infect new hosts. In the parasites that cause malaria , for instance, the sporozoites are cells that develop in the mosquito's salivary glands, leave the mosquito during a blood meal, and enter the liver where they multiply...
s. These sporozoites migrate to the salivary glands of the mosquito where they are injected into the blood and subcutaneous tissue of the next host the mosquito bites. The majority appear to be injected into the subcutaneous tissue from which they migrate into the capillaries. A proportion are ingested by macrophages and still others are taken up by the lymphatic system where they are presumably destroyed. The sporozoites which successfully enter the blood stream move to the liver where they begin the cycle again.
The pattern of alternation of sexual and asexual reproduction which may seem confusing at first is a very common pattern in parasitic species. The evolutionary advantages of this type of life cycle were recognised by Mendel.
Under favourable conditions asexual reproduction is superior to sexual as the parent is well adapted to its environment and its descendents share these genes. Transferring to a new host or in times of stress, sexual reproduction is generally superior as this produces a shuffling of
genesGênes is the name of a département of the First French Empire in present Italy. It was named after the city Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa. It was divided into the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
which on average at a population level will produce individuals better adapted to the new environment.
Reactivation of the hypnozoites has been reported for up to 30 years after the initial infection in humans. The factors precipating this reactivation are not known. In the species
Plasmodium malariaePlasmodium malariae is a parasitic protozoa that causes malaria in humans. It is closely related to Plasmodium falciparum and Plasmodium vivax which are responsible for most malarial infection. While found worldwide, it is a so-called "benign malaria" and is not nearly as dangerous as that...
,
Plasmodium ovalePlasmodium ovale is a species of parasitic protozoa that causes tertian malaria in humans. It is closely related to Plasmodium falciparum and Plasmodium vivax, which are responsible for most malaria. It is rare compared to these two parasites, and substantially less dangerous than P...
and
Plasmodium vivaxPlasmodium vivax is a protozoal parasite and a human pathogen. The most frequent and widely distributed cause of recurring malaria, P. vivax is one of four species of malarial parasite that commonly infect humans. It is less virulent than Plasmodium falciparum, which is the deadliest of the four,...
hypnozoites have been shown to occur. Reactivation was not thought to occur in infections with
Plasmodium falciparumPlasmodium falciparum is a protozoan parasite, one of the species of Plasmodium that cause malaria in humans. It is transmitted by the female...
but there has been several reports to date suggesting that this may occur (see below). It is not yet known if hypnozoite reactivaction occurs with any of the remaining species that infect humans but this is presumed to be the case.
Possible relapses of Plasmodium falciparum malaria
A report of
P. falciparum malaria in a patient with sickle cell anemia four years after exposure to the parasite has been published. A second report that
P. falciparum malaria had become symptomatic eight years after leaving an endemic area has also been published.
A third case of an apparent recurrence nine years after leaving an endemic area of
P. falciparum malaria has now been reported . A fourth case of recurrence in a patient with lung cancer has been reported. Two cases in pregnant women both from Africa but who had not lived there for over a year have been reported.
It seems that at least occasionally
P. falciparum has a dormant stage. If this is in fact the case, eradication or control of this organism may be more difficult than previously believed.
Potentially dormant forms of Plasmodium
A small number of potentially dormant forms of
Plasmodium parasites both
in vitro and
in vivo have been observed.
The schizont stage-infected erythrocyte in an experimental culture of
P. falciparum, F32 was suppressed to a low level with the use of atovaquone. The parasites resumed growth several days after the drug was removed from the culture.
More than a hundred late-stage trophozoites or early schizont infected erythrocytes of
P. falciparum in a case of placental malaria of a Tanzanian woman were found to form a nidus in an intervillous space of placenta. While such a concentration of parasites in placental malaria is rare, placental malaria cannot give rise to persistent infection as pregnancy in humans normally lasts only 9 months.
Macrophages containing merozoites dispersed in their cytoplasm, called 'merophores', were observed in
P. vinckei petteriPlasmodium vinckei is a parasite of the genus Plasmodium subgenus Vinckeia.Like all Plasmodium species P. vinckei has both vertebrate and insect hosts. The vertebrate hosts for this parasite are rodents.- Geographical occurrence :...
- an organism that causes murine malaria. Similar merophores were found in the polymorph leukocytes and macrophages of other murine malaria parasite,
P. yoelii nigeriensisPlasmodium yoelii is a parasite of the genus Plasmodium subgenus Vinckeia.Like all Plasmodium species P. yoelii has both vertebrate and insect hosts. The vertebrate hosts for this parasite are mammals.- Notes :...
and
P. chabaudi chabaudiPlasmodium chabaudi is a parasite of the genus Plasmodium subgenus Vinckeia.Like all Plasmodium species P. chabaudi has both vertebrate and insect hosts. The vertebrate hosts for this parasite are mammals.- Description :...
. All these species unlike
P. falciparum are known to produce hyponozoites that may cause a relapse. The finding of Landau
et al. on the presence of malaria parasites inside lymphatics suggest a mechanism for the recrudescence and chronicity of malaria infection.
Evolution
This probably best understood in terms of its
evolutionIn biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a...
. At the present time (2007) DNA sequences are available from fewer than sixty species of
Plasmodium and most of these are from species infecting either rodent or primate hosts. The evolutionary outline given here should be regarded as speculative and subject to revision as data becomes available.
The
ApicomplexaThe Apicomplexa are a large group of protists, most of which possess a unique organelle called apicoplast and an apical complex structure involved in penetrating a host's cell. They are unicellular, spore-forming, and exclusively parasites of animals. Motile structures such as flagella or...
— the phylum to which
Plasmodium belongs - are thought to have originated within the
DinoflagellateThe dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth. About half of all dinoflagellates are photosynthetic, and these make up the...
s — a large group of photosynthetic protists. It is thought that the ancestors of the Apicomplexa were originally prey organisms that evolved the ability to invade the intestinal cells and subsequently lost their photosynthetic ability. Many of the species within the Apicomplexia still possess a plastid (the organelle in which photosynthesis occurs in photosynthetic eukaryotes), and some that do not have evidence of plastid genes within their genomes. These plastids are not capable of
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
. Their function is not known, but there is suggestive evidence that they may be involved in reproduction.
Some extant dinoflagelates, however, can invade the bodies of
jellyfishJellyfish are free-swimming members of the phylum Cnidaria. Jellyfish have several different morphologies that represent several different cnidarian classes including the Scyphozoa , Staurozoa , Cubozoa , and Hydrozoa Jellyfish (also known as jellies or sea jellies) are free-swimming members of...
and continue to photosynthesize, which is possible because jellyfish bodies are almost transparent. In other organisms with
opaqueOpacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...
bodies this ability would most likely rapidly be lost. The recent (2008) description of a photosynthetic protist related to the Apicomplexia with a functional plastid supports this hypothesis.
Current (2007) theory suggests that the genera
Plasmodium,
Hepatocystis and
HaemoproteusHaemoproteus is a genus of protozoa that are parasitic in birds, reptiles and amphibians. The genus created was by Kruse in 1890. Its name is derived from Greek: Haima - blood and Proteus - a sea god who had the power of assuming different shapes...
evolved from one or more
LeukocytozoonLeukocytozoon is a genus of parasitic protozoa belonging to the phylum Apicomplexia. The parasites were first seen by Danilewsky in 1884. The genus was created by Ziemann in 1898...
species. Parasites of the genus
Leukocytozoan infect white blood cells (leukocytes),
liverThe liver is a vital organ present in vertebrates and some other animals; it has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
and
spleenThe spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells, holds a reserve in case of hemorrhagic shock, especially in...
cells and are transmitted by 'black flies' (
SimuliumSimulium is a genus of black flies. It is an immense genus with several hundred species, and 41 sub-genera.-Systematics:Sub-genera:*Afrosimulium
Crosskey, 1969*Anasolen
Enderlein, 1930...
species) — a large genus of flies related to the mosquitoes.
It is thought that
Leukocytozoon evolved from a parasite that spread by the orofaecal route and which infected the intestinal wall. At some point this parasite evolved the ability to infect the
liverThe liver is a vital organ present in vertebrates and some other animals; it has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
. This pattern is seen in the genus
Cryptosporidium to which
Plasmodium is distantly related. At some later point this ancestor developed the ability to infect blood cells and to survive and infect
mosquitoMosquito is a common insect in the family Culicidae...
es. Once vector transmission was firmly established, the previous orofecal route of transmission was lost.
Molecular evidence suggests that repitles - specifically a squamate - was the first vertebrate host of
Plasmodium. Birds were the second vertebrate hosts with mammals being the most recent group of vertebrates infected..
Leukocytes,
hepatocyteHepatocytes make up 70-80% of the cytoplasmic mass of the liver.These cells are involved in protein synthesis, protein storage and transformation of carbohydrates, synthesis of cholesterol, bile salts and phospholipids, and detoxification, modification and excretion of exogenous and endogenous...
s and most spleen cells actively phagocytose particulate matter making entry into the cell easier for the parasite. The mechanism of entry of
Plasmodium species into erythrocytes is still very unclear taking as it does less than 30 seconds. It is not yet known if this mechanism evolved before mosquitoes became the main vectors for transmission of
Plasmodium.
The genus
Plasmodium evolved (presumably from its
Leukocytozoon ancestor) about 130 million years ago, a period that is coincidental with the rapid spread of the angiosperms (flowering plants). This expansion in the angiosperms is thought to be due to at least one genomic duplication event. It seems probable that the increase in the number of flowers led to an increase in the number of mosquitoes and their contact with vertebrates.
Mosquitoes evolved in what is now
South AmericaSouth America is the southern continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere...
about 230 million years ago. There are over 3500 species recognized, but to date their evolution has not been well worked out, so a number of gaps in our knowledge of the evolution of
Plasmodium remain.
There is evidence of a recent expansion of
Anopheles gambiaeAnopheles gambiae is a complex of at least seven morphologically indistinguishable species of mosquitoes in the genus Anopheles. This complex was recognised in the 1960s and includes the most important vectors of malaria in Sub-Saharan Africa and the most efficient malaria vectors known.This...
and
Anopheles arabiensis populations in the late
PleistoceneThe Pleistocene is the epoch from 2.588 million to 12 000 years BP covering the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
in
NigeriaNigeria , officially the Federal Republic of Nigeria, is a federal constitutional republic comprising thirty-six states and one Federal Capital Territory. The country is located in West Africa and shares land borders with the Republic of Benin in the west, Chad and Cameroon in the east, and Niger...
.
Biology
All
Plasmodium species examined to date have 14 chromosomes, with one
mitochondrionIn cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5–10 micrometers in diameter...
and one
plastidPlastids are major organelles found in the cells of plants and algae. Plastids are the site of manufacture and storage of important chemical compounds used by the cell...
genome. The chromosomes whose length is known vary from 500 kilobases to 3.5 megabases in length. It is presumed that this is the pattern throughout the genus. The typical chormosome number of
Leukcytozoon has not yet been established.
The genome of four Plasmodium species have been sequenced. These species are
Plasmodium falciparumPlasmodium falciparum is a protozoan parasite, one of the species of Plasmodium that cause malaria in humans. It is transmitted by the female...
,
Plasmodium knowlesiPlasmodium knowlesi is a primate malaria parasite commonly found in Southeast Asia. It causes malaria in long-tailed macaques , but it may also infect humans, either naturally or artificially....
,
Plasmodium vivaxPlasmodium vivax is a protozoal parasite and a human pathogen. The most frequent and widely distributed cause of recurring malaria, P. vivax is one of four species of malarial parasite that commonly infect humans. It is less virulent than Plasmodium falciparum, which is the deadliest of the four,...
and
Plasmodium yoelli. All these species have 14 chromosomes and genomes of about 25 megabases, results consistent with earlier estimates.
The biology of these organisms is more fully described on the
Plasmodium falciparum biology pagePlasmodium falciparum has been the focus of much research due to it being the causative agent of malaria. This article describes some of the recent findings surrounding the unique biology of this organism.-Life Cycle:...
.
Taxonomy
Plasmodium belongs to the
familyFamily denotes a group of people or animals affiliated by a consanguinity, affinity or co-residence...
PlasmodiidaeThe Plasmodiidae are a family of apicomplexan parasites, including the type genus Plasmodium, which is responsible for malaria. This genus was created in 1903 by Mesnil.They are given their own order - the Haemosporida.- Diagnostic criteria :...
(Levine, 1988),
orderIn scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Haemosporidia and
phylumIn biology, a phylum ["Phylum" is adopted from the Greek phylai, the clan-based voting groups in Greek city-states.] is a taxonomic rank below Kingdom and above Class...
ApicomplexaThe Apicomplexa are a large group of protists, most of which possess a unique organelle called apicoplast and an apical complex structure involved in penetrating a host's cell. They are unicellular, spore-forming, and exclusively parasites of animals. Motile structures such as flagella or...
. There are currently 450 recognised
speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
in this order. Many species of this order are undergoing reexamination of their taxonomy with
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
analysis. It seems likely that many of these species will be re-assigned after these studies have been completed. For this reason the entire order is outlined here.
Order Haemosporida
- Genus Bioccala
Bioccala is a genus of parasitic protozoa belonging to the phylum Apicomplexia.- Host range :The only known host of these parasites is the bat Hipposideros larvatus....
Family Haemoproteidae
- Genus Haemoproteus
Haemoproteus is a genus of protozoa that are parasitic in birds, reptiles and amphibians. The genus created was by Kruse in 1890. Its name is derived from Greek: Haima - blood and Proteus - a sea god who had the power of assuming different shapes...
- Subgenus Parahaemoproteus
- Subgenus Haemoproteus
Haemoproteus is a genus of protozoa that are parasitic in birds, reptiles and amphibians. The genus created was by Kruse in 1890. Its name is derived from Greek: Haima - blood and Proteus - a sea god who had the power of assuming different shapes...
Family Garniidae
Family Leucocytozoidae
- Genus Leukocytozoon
Leukocytozoon is a genus of parasitic protozoa belonging to the phylum Apicomplexia. The parasites were first seen by Danilewsky in 1884. The genus was created by Ziemann in 1898...
- Subgenus Leucocytozoon
- Subgenus Akiba
Akiba Also pronounced Akiva can refer to:*The Aramaic form of the name Jacob*Akiba-Schechter Jewish Day School, a Jewish school in Hyde Park, Chicago*Akiva, a tannaitic Rabbi*Akiba Hebrew Academy, a Jewish school in Merion, Pennsylvania...
Family
PlasmodiidaeThe Plasmodiidae are a family of apicomplexan parasites, including the type genus Plasmodium, which is responsible for malaria. This genus was created in 1903 by Mesnil.They are given their own order - the Haemosporida.- Diagnostic criteria :...
- Genus Billbraya
- Genus Dionisia
Dionisia is a genus of parasitic protozoa belonging to the phylum Apicomplexia.The type species of this genus is Dionisia bunoi.- Description :The genus was described by Landau et al. in 1980...
- Genus Hepatocystis
- Genus Mesnilium
- Genus Nycteria
- Genus Plasmodium
- Subgenus Asiamoeba
Asiamoeba is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created by Telford in 1988. Species in this subgenus infect lizards.- Diagnostic features :...
- Subgenus Bennettinia
Bennettinia is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1997 by Valkiunas. Species in this subgenus infect birds.- Diagnostic features :...
- Subgenus Carinamoeba
Carinamoeba is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1966 by Garnham. Species in this subgenus infect reptiles.- Diagnostic features :...
- Subgenus Fallisia
- Subgenus Garnia
- Subgenus Giovannolaia
Giovanolaia is a subgenus of the genus Plasmodium created by Corradetti et al. in 1963. The parasites within this subgenus infect birds.- Diagnostic features :Species in the subgenus Giovanolaia have the following characteristics:...
- Subgenus Haemamoeba
Haemamoeba is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1963 by created by Corradetti et al....
- Subgenus Huffia
Huffia is a subgenus of the genus Plasmodium - all of which are parasitic protozoa. The subgenus was created in 1963 by Corradetti et al....
- Subgenus Lacertaemoba
Lacertaemoba is a subgenus of the genus Plasmodium - all of which are parasitic protozoa. All species in this subgenus infect reptiles.This subgenus was created by Telford to refine the classification of species then given as Plasmodium tropiduri....
- Subgenus Laverania
Laverania is a subgenus of the genus Plasmodium. The subgenus was created in 1958 by Bray. The subgenus contains only species: Plasmodium falciparum and Plasmodium reichenowi....
- Subgenus Novyella
Novyella is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1963 by created by Corradetti et al.. Species in this subgenus infect birds...
- Subgenus Ophidiella
Ophidiella is a subgenus of the genus Plasmodium created in 1966 by Garnham. .It was created as a subgenus for the then only known species infecting snakes - Plasmodium wenyoni.- Species in this subgenus :Plasmodium pessoai
...
- Subgenus Plasmodium
- Subgenus Paraplasmodium
- Subgenus Sauramoeba
Sauramoeba is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1966 by Garnham. Species in this subgenus infect reptiles.- Diagnostic features :...
- Subgenus Vinckeia
Vinckeia is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus Vinckeia was created by Garnham in 1966 to accommodate the mammalian parasites other than those infecting the primates.- Diagnostic features :...
- Genus Polychromophilus
- Genus Rayella
- Genus Saurocytozoon
Diagnostic characteristics of the genus Plasmodium
- Merogony occurs both in erythrocytes and other tissues
- Merozoites, schizonts or gametocytes can be seen within erythrocytes and may displace the host nucleus
- Merozoites have a “signet-ring” appearance due to a large vacuole that forces the parasite’s nucleus to one pole
- Schizonts are round to oval inclusions that contain the deeply staining merozoites
- Forms gamonts in erythrocytes
- Gametocytes are 'halter-shaped' similar to Haemoproteus
Haemoproteus is a genus of protozoa that are parasitic in birds, reptiles and amphibians. The genus created was by Kruse in 1890. Its name is derived from Greek: Haima - blood and Proteus - a sea god who had the power of assuming different shapes...
but the pigment granules are more confined
- Hemozoin is present (except in the subgenus Garnia)
- Vectors are either mosquitos or sandflies
- Vertebrate hosts include mammals, birds and reptiles
Phylogenetic trees
The relationship between a number of these species can be seen on the
Tree of Life website. Perhaps the most useful inferences that can be drawn from this
phylogenetic treeA phylogenetic tree or evolutionary tree is a tree showing the evolutionary relationships among various biological species or other entities that are believed to have a common ancestor. In a phylogenetic tree, each node with descendants represents the most recent common ancestor of the...
are:
- P. falciparum and P. reichenowi (subgenus Laverania) branched off early in the evolution of this genus
- The genus Hepatocystis is nested within (paraphytic with) the genus Plasmodium
- The primate (subgenus Plasmodium) and rodent species (subgenus Vinckeia) form distinct groups
- The rodent and primate groups are relatively closely related
- The lizard and bird species are intermingled
- Although Plasmodium elongatum (subgenus Haemamoeba) and Plasmodium elongatum (subgenus Huffia) appear be related here there are so few bird species (three) included, this tree may not accurately reflect their real relationship.
- While no snake parasites have been included these are likely to group with the lizard-bird division
While this tree contains a considerable number of species, DNA sequences from many species in this genus have not been included - probably because they are not available yet. Because of this problem, this tree and any conclusions that can be drawn from it should be regarded as provisional.
Three additional trees are available from the
American Museum of Natural History.
These trees agree with the Tree of Life. Because of their greater number of species in these trees, some additional inferences can be made:
- The genus Hepatocystis appears to lie within the primate-rodent clade
- The genus Haemoproteus appears lie within the bird-lizard clade
- The trees are consistent with the proposed origin of Plasmodium from Leukocytozoon
It is also known that the species infecting humans do not form a single clade. In contrast, the species infecting Old World monkeys seem to form a clade.
Plasmodium vivaxPlasmodium vivax is a protozoal parasite and a human pathogen. The most frequent and widely distributed cause of recurring malaria, P. vivax is one of four species of malarial parasite that commonly infect humans. It is less virulent than Plasmodium falciparum, which is the deadliest of the four,...
may have originated in
AsiaAsia is the world's largest and most populous continent, located in the eastern and northern hemispheres. It covers 8.6% of the earth's total surface area and with approximately 4 billion people, it hosts 60% of the world's current human population.Asia is traditionally defined as part of the...
and the related species
Plasmodium simium appears to be derived through a transfer from the human
P. vivax to
New WorldThe New World is one of the names used for the non-Afro-Eurasian parts of the Earth, specifically the Americas and possibly Australia. When the term originated in the late 15th century, the Americas were new to the Europeans, who previously thought of the world as consisting only of Europe, Asia,...
monkeyA monkey is any cercopithecoid or platyrrhine primate. All primates that are not prosimians or apes are monkeys. The 264 known extant monkey species represent two of the three groupings of simian primates...
species in
South AmericaSouth America is the southern continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere...
.
Another tree concetrating on the species infecting the primates is available here:
PLOS site
This tree shows that the 'African' (
P. malaria and
P. ovale) and 'Asian' (
P.cynomogli,
P. gonderi,
P. semiovale and
P. simium) species tend to cluster together into separate clades.
P. vivax clusters with the 'Asian' species. The rodent species (
P. bergei,
P. chabaudi and
P. yoelli) form a separate clade. As usual
P. falciparum does not cluster with any other species. The bird species (
P. juxtanucleare,
P. gallinaceum and
P. relictum) form a clade that is related to the included
Leukocytozoan and
Haemoproteus species.
P. vivax appears to have evolved between 45,000 and 82,000 years ago from a species that infects south east Asian macques. This is consistent with the other evidence of a south eastern origin of this species.
It has been reported that the C terminal domain of the RNA polymerase 2 in the primate infecting species (other than
P. falciparum and probably
P. reichenowei) appears to be unusual suggesting that the classification of species into the subgenus
Plasmodium may have an evolutionary and biological basis.
Unlike other eukaryotes studied to date
Plasmodium species have two or three distinct SSU rRNA (18S rRNA) molecules encoded within the genome. These have been divided into types A, S and O. Type A is expressed in the asexual stages; type S in the sexual and type O only in the oocyte. Type O is only known to occur in
Plasmodium vivaxPlasmodium vivax is a protozoal parasite and a human pathogen. The most frequent and widely distributed cause of recurring malaria, P. vivax is one of four species of malarial parasite that commonly infect humans. It is less virulent than Plasmodium falciparum, which is the deadliest of the four,...
at present. The reason for this gene duplication is not known but presumably reflects an adaption to the different environments the parasite lives within.
The Asian simian
Plasmodium species -
Plasmodium coatneyi,
Plasmodium cynomolgi,
Plasmodium fragile,
Plasmodium inui,
Plasmodium fieldiPlasmodium fieldi is a parasite of the genus Plasmodium sub genus Plasmodium found in Malaysia.This species is related to Plasmodium ovale and Plasmodium simiovale. Like all Plasmodium species P. fieldi has both vertebrate and insect hosts...
,
Plasmodium hylobati and
Plasmodium simiovale - have a single single S-type-like gene and several A-type-like genes. It seems likely that these species form a clade within the subgenus
Plasmodium.
A report of a new species that clusters with
P. falciparum and
P. reichenowi in chimpanzees has been published, although to date the species has been identified only from the sequence of its mitochondrion. Further work will be needed to describe this new species, however, it appears to have diverged from the
P. falciparum-
P. reichenowi clade about 21 million years ago.
It has been shown that
P. falciparum forms a clade with the species
P reichenowi. This clade may have originated between 3 million and 10000 years ago. It is proposed that the origin of
P. falciparum may have occurred when its precursors developed the ability to bind to sialic acid Neu5Ac possibly via erythrocyte binding protein 175. Humans lost the ability to make the sialic acid Neu5Gc from its precursor Neu5Ac several million years ago and this may have protected them against infection with
P. reichenowi.
A recently (2009) described species (
Plasmodium hydrochaeriPlasmodium hydrochaeri is a parasite of the genus Plasmodium subgenus Vinckeia.Like all Plasmodium species P. hydrochaeri has both vertebrate and insect hosts. The vertebrate hosts for this parasite are rodents.- Description :...
) that infects capybaras (
Hydrochaeris hydrochaeris) may complicate the phylogentics of this genus. This species appears to be most similar to
Plasmodium mexicanumPlasmodium mexicanum is a parasite of the genus Plasmodium.Like all Plasmodium species P. mexicanum has both vertebrate and insect hosts. The vertebrate hosts for this parasite are reptiles.- Clinical features and host pathology :...
a lizard parasite. Further work in this area seems indicated.
Subgenera: discussion
The full taxonomic name of a species includes the subgenus but this is often omitted. The full name indicates some features of the morphology and type of host species. Sixteen subgenera are currently recognised.
Mammalian species
The only two species in the subgenus
LaveraniaLaverania is a subgenus of the genus Plasmodium. The subgenus was created in 1958 by Bray. The subgenus contains only species: Plasmodium falciparum and Plasmodium reichenowi....
are
P. falciparum and
P. reichenowi. A third species -
Plasmodium gaboni - may also exist but a full description of this species has not yet been published. The presence of elongated gametocytes in several of the avian subgenera and in
Laverania in addition to a number of clinical features suggested that these might be closely related. This is no longer thought to be the case.
The type species is
Plasmodium falciparumPlasmodium falciparum is a protozoan parasite, one of the species of Plasmodium that cause malaria in humans. It is transmitted by the female...
.
Species infecting
monkeyA monkey is any cercopithecoid or platyrrhine primate. All primates that are not prosimians or apes are monkeys. The 264 known extant monkey species represent two of the three groupings of simian primates...
s and apes (the higher primates) with the exceptions of
P. falciparum and
P. reichenowi are classified in the subgenus
Plasmodium. The distinction between
P. falciparum and
P. reichenowi and the other species infecting higher primates was based on the morphological findings but have since been confirmed by DNA analysis.
The type species is
Plasmodium malariaePlasmodium malariae is a parasitic protozoa that causes malaria in humans. It is closely related to Plasmodium falciparum and Plasmodium vivax which are responsible for most malarial infection. While found worldwide, it is a so-called "benign malaria" and is not nearly as dangerous as that...
.
Parasites infecting other
mammalMammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.Mammals are divided into three main...
s including lower primates (
lemurA lemur is a member of the biological infraorder Lemuriformes, a prosimian and strepsirrhine primate that is endemic to the island of Madagascar. The term "lemur" is derived from the Latin word lemures, meaning "spirits of the night" or "haunter". This likely refers to their large, reflective eyes...
s and others) are classified in the subgenus
VinckeiaVinckeia is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus Vinckeia was created by Garnham in 1966 to accommodate the mammalian parasites other than those infecting the primates.- Diagnostic features :...
.
Vinckeia while previously considered to be something of a taxonomic 'rag bag' has been recently shown - perhaps rather surprisingly - to form a coherent grouping.
The type species is
Plasmodium bubalisPlasmodium bubalis is a parasite of the genus Plasmodium subgenus Vinckeia.Like all Plasmodium species P. bubalis has both vertebrate and insect hosts. The vertebrate hosts for this parasite are mammals.- Description :...
.
Birds
The remaining groupings are based on the morphology of the parasites. Revisions to this system are likely to occur in the future as more species are subject to analysis of their
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
.
The four subgenera
GiovannolaiaGiovanolaia is a subgenus of the genus Plasmodium created by Corradetti et al. in 1963. The parasites within this subgenus infect birds.- Diagnostic features :Species in the subgenus Giovanolaia have the following characteristics:...
,
HaemamoebaHaemamoeba is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1963 by created by Corradetti et al....
,
HuffiaHuffia is a subgenus of the genus Plasmodium - all of which are parasitic protozoa. The subgenus was created in 1963 by Corradetti et al....
and
NovyellaNovyella is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1963 by created by Corradetti et al.. Species in this subgenus infect birds...
were created by Corradetti
et al. for the known avian malarial species. A fifth—
BennettiniaBennettinia is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1997 by Valkiunas. Species in this subgenus infect birds.- Diagnostic features :...
—was created in 1997 by Valkiunas. The relationships between the subgenera are the matter of current investigation. Martinsen
et al. 's recent (2006) paper outlines what is currently (2007) known. The subgenera
Haemamoeba,
Huffia, and
Bennettinia appear to be monphylitic.
Novyella appears to be well defined with occasional exceptions. The subgenus
Giovannolaia needs revision.
P. juxtanucleare is currently (2007) the only known member of the subgenus
Bennettinia.
Nyssorhynchus is an extinct subgenus of
Plasmodium. It has one known member -
Plasmodium dominicum
Reptiles
Unlike the mammalian and bird malarias those species (>90 known) that infect reptiles have been more difficult to classify.
In 1966 Garnham classified those with large schizonts as
SauramoebaSauramoeba is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1966 by Garnham. Species in this subgenus infect reptiles.- Diagnostic features :...
, those with small schizonts as
CarinamoebaCarinamoeba is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1966 by Garnham. Species in this subgenus infect reptiles.- Diagnostic features :...
and the single then known species infecting snakes (
Plasmodium wenyoniPlasmodium wenyoni is a parasite of the genus Plasmodium.Like all Plasmodium species P. wenyoni has both vertebrate and insect hosts. The vertebrate hosts for this parasite are reptiles.- Description :...
) as
OphidiellaOphidiella is a subgenus of the genus Plasmodium created in 1966 by Garnham. .It was created as a subgenus for the then only known species infecting snakes - Plasmodium wenyoni.- Species in this subgenus :Plasmodium pessoai
...
. He was aware of the arbitrariness of this system and that it might not prove to be biologically valid. Telford in 1988 used this scheme as the basis for the currently accepted (2007) system.
These species have since been divided in to 8 genera -
AsiamoebaAsiamoeba is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created by Telford in 1988. Species in this subgenus infect lizards.- Diagnostic features :...
,
CarinamoebaCarinamoeba is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1966 by Garnham. Species in this subgenus infect reptiles.- Diagnostic features :...
,
Fallisia,
Garnia,
Lacertamoeba,
OphidiellaOphidiella is a subgenus of the genus Plasmodium created in 1966 by Garnham. .It was created as a subgenus for the then only known species infecting snakes - Plasmodium wenyoni.- Species in this subgenus :Plasmodium pessoai
...
,
Paraplasmodium and
SauramoebaSauramoeba is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1966 by Garnham. Species in this subgenus infect reptiles.- Diagnostic features :...
. Three of these genera (
Asiamoeba,
Lacertamoeba and
Paraplasmodium) were created by Telford in 1988. Another species (
Billbraya australis) described in 1990 by Paperna and Landau and is the only known species in this genus. This species may turn out to be another subgenus of lizard infecting
Plasmodium.
Bird species
There are ~40 recognised bird species. Although over 50 species have been described, several have been rejected as being invalid.
With the exception of
P. elongatum the exoerythrocytic stages occur in the endothelial cells and those of the macrophage-lymphoid system. The exoerythrocytic stages of
P. elongatum parasitise the blood forming cells.
The various subgenera are first distinguished on the basis of the morphology of the mature gametocytes. Those of subgenus
Haemamoeba are round or oval while those of the subgenera
Giovannolaia,
Huffia and
Novyella are elongated. These latter genera are distinguished on the basis of the size of the schizonts:
Giovannolaia and
Huffia have large schizonts while those of
Novyella are small.
Species in the subgenus
BennettiniaBennettinia is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1997 by Valkiunas. Species in this subgenus infect birds.- Diagnostic features :...
have the following characteristics:
The type species is
Plasmodium juxtanuclearePlasmodium juxtanucleare is a parasite of the genus Plasmodium subgenus Bennettinia.Like all Plasmodium species P. juxtanucleare has both vertebrate and insect hosts. The vertebrate hosts for this parasite are birds.- Description :...
.
Species in the subgenus
GiovannolaiaGiovanolaia is a subgenus of the genus Plasmodium created by Corradetti et al. in 1963. The parasites within this subgenus infect birds.- Diagnostic features :Species in the subgenus Giovanolaia have the following characteristics:...
have the following characteristics:
- Schizonts contain plentiful cytoplasm, are larger than the host cell nucleus and frequently displace it. They are found only in mature erythrocytes.
- Gametocytes are elongated.
- Exoerythrocytic schizogony occurs in the mononuclear phagocyte system.
The type species is
Plasmodium circumflexumPlasmodium circumflexum is a parasite of the genus Plasmodium subgenus Giovannolaia.Like all Plasmodium species P. circumflexum has both vertebrate and insect hosts. The vertebrate hosts for this parasite are birds.-Description:...
.
Species in the subgenus
HaemamoebaHaemamoeba is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1963 by created by Corradetti et al....
have the following characteristics:
- Mature schizonts are larger than the host cell nucleus and commonly displace it.
- Gametocytes are large, round, oval or irregular in shape and are substantially larger than the host nucleus.
The type species is
Plasmodium relictum.
Species in the subgenus
HuffiaHuffia is a subgenus of the genus Plasmodium - all of which are parasitic protozoa. The subgenus was created in 1963 by Corradetti et al....
have the following characteristics:
- Mature schizonts, while varying in shape and size, contain plentiful cytoplasm and are commonly found in immature erthryocytes.
- Gametocytes are elongated.
The type species is
Plasmodium elongatum.
Species in the subgenus
NovyellaNovyella is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1963 by created by Corradetti et al.. Species in this subgenus infect birds...
have the following characteristics:
- Mature schizonts are either smaller than or only slightly larger than the host nucleus. They contain scanty cytoplasm.
- Gametocytes are elongated. Sexual stages in this subgenus resemble those of Haemoproteus.
- Exoerythrocytic schizogony occurs in the mononuclear phagocyte system
The type species is
Plasmodium vaughaniPlasmodium vaughani is a parasite of the genus Plasmodium subgenus Novyella.Like all Plasmodium species P. vaughani has both vertebrate and insect hosts. The vertebrate hosts for this parasite are birds.- Description :...
.
Reptile species
All species in these subgenera infect lizards.
Species in the subgenus
AsiamoebaAsiamoeba is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created by Telford in 1988. Species in this subgenus infect lizards.- Diagnostic features :...
have the following characteristics:
Species in the subgenus
CarinamoebaCarinamoeba is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1966 by Garnham. Species in this subgenus infect reptiles.- Diagnostic features :...
have the following characteristics:
- Schizonts normally give rise to less than 8 merozoites
- Schizonts are normally smaller than the host nucleus
The type species is
Plasmodium minasensePlasmodium minasense is a parasite of the genus Plasmodium subgenus Carinamoeba.Like all Plasmodium species P. minasense has both vertebrate and insect hosts. The vertebrate hosts for this parasite are lizards.- Description :...
.
Species in the subgenus
Fallisia have the following characteristics:
- Non-pigmented asexual and gametocyte forms are found in leukocytes and thrombocytes
Species in the subgenus
Garnia have the following characteristics:
Species in the subgenus
LacertaemobaLacertaemoba is a subgenus of the genus Plasmodium - all of which are parasitic protozoa. All species in this subgenus infect reptiles.This subgenus was created by Telford to refine the classification of species then given as Plasmodium tropiduri....
have the following characteristics:
Species in the subgenus
Paraplasmodium have the following characteristics:
Species in the subgenus
SauramoebaSauramoeba is a subgenus of the genus Plasmodium - all of which are parastic protozoa. The subgenus was created in 1966 by Garnham. Species in this subgenus infect reptiles.- Diagnostic features :...
have the following characteristics:
- Schizonts normally give rise to more than 8 merozoites
- Schizonts are normally larger than the host nucleus
- Non-pigmented gametocytes are typically the only forms found
- Pigmented forms may be found in the leukocytes occasionally
The type species is
Plasmodium agamaePlasmodium agamae is a parasite of the genus Plasmodium subgenus Sauramoeba.Like all Plasmodium species it has both vertebrate and insect hosts. The vertebrate host is the rainbow lizard Agama agama...
.
All species in
OphidiellaOphidiella is a subgenus of the genus Plasmodium created in 1966 by Garnham. .It was created as a subgenus for the then only known species infecting snakes - Plasmodium wenyoni.- Species in this subgenus :Plasmodium pessoai
...
infect snakes
The type species is
Plasmodium weyoni.
Notes
- The erythrocytes of both reptiles and birds retain their nucleus, unlike those of mammals. The reason for the loss of the nucleus in mammalian erythocytes remains unknown.
Species listed by subgenera
Plasmodium (Asiamoeba) clelandi
Plasmodium (Asiamoeba) draconis
Plasmodium (Asiamoeba) lionatum
Plasmodium (Asiamoeba) saurocordatum
Plasmodium (Asiamoeba) vastator
Plasmodium (Bennettinia) juxtanucleare
Plasmodium (Carinamoeba) basilisci
Plasmodium (Carinamoeba) clelandi
Plasmodium (Carinamoeba) lygosomae
Plasmodium (Carinamoeba) mabuiae
Plasmodium (Carinamoeba) minasense
Plasmodium (Carinamoeba) rhadinurum
Plasmodium (Carinamoeba) volans
Plasmodium (Fallisia) siamense
Plasmodium (Giovannolaia) anasum
Plasmodium (Giovannolaia) circumflexum
Plasmodium (Giovannolaia) dissanaikei
Plasmodium (Giovannolaia) durae
Plasmodium (Giovannolaia) fallax
Plasmodium (Giovannolaia) formosanum
Plasmodium (Giovannolaia) gabaldoni
Plasmodium (Giovannolaia) garnhami
Plasmodium (Giovannolaia) gundersi
Plasmodium (Giovannolaia) hegneri
Plasmodium (Giovannolaia) lophurae
Plasmodium (Giovannolaia) pedioecetii
Plasmodium (Giovannolaia) pinnotti
Plasmodium (Giovannolaia) polare
Plasmodium (Haemamoeba) cathemerium
Plasmodium (Haemamoeba) coggeshalli
Plasmodium (Haemamoeba) coturnixi
Plasmodium (Haemamoeba) elongatum
Plasmodium (Haemamoeba) gallinaceum
Plasmodium (Haemamoeba) giovannolai
Plasmodium (Haemamoeba) lutzi
Plasmodium (Haemamoeba) matutinum
Plasmodium (Haemamoeba) paddae
Plasmodium (Haemamoeba) parvulum
Plasmodium (Haemamoeba) relictum
Plasmodium (Haemamoeba) tejera
Plasmodium (Huffia) elongatum
Plasmodium (Huffia) hermani
Plasmodium (Lacertaemoba) floridense
Plasmodium (Lacertaemoba) tropiduri
Plasmodium (Laverania) falciparum
Plasmodium (Laverania) reichenowi
Plasmodium (Ophidiella) pessoai
Plasmodium (Ophidiella) tomodoni
Plasmodium (Ophidiella) wenyoni
Plasmodium (Novyella) ashfordi
Plasmodium (Novyella) bertii
Plasmodium (Novyella) bambusicolai
Plasmodium (Novyella) columbae
Plasmodium (Novyella) corradettii
Plasmodium (Novyella) dissanaikei
Plasmodium (Novyella) globularis
Plasmodium (Novyella) hexamerium
Plasmodium (Novyella) jiangi
Plasmodium (Novyella) kempi
Plasmodium (Novyella) lucens
Plasmodium (Novyella) megaglobularis
Plasmodium (Novyella) multivacuolaris
Plasmodium (Novyella) nucleophilum
Plasmodium (Novyella) papernai
Plasmodium (Novyella) parahexamerium
Plasmodium (Novyella) paranucleophilum
Plasmodium (Novyella) rouxi
Plasmodium (Novyella) vaughani
Plasmodium (Nyssorhynchus) dominicum
Plasmodium (Paraplasmodium) chiricahuae
Plasmodium (Paraplasmodium) mexicanum
Plasmodium (Paraplasmodium) pifanoi
Plasmodium (Plasmodium) bouillize
Plasmodium (Plasmodium) brasilianum
Plasmodium (Plasmodium) cercopitheci
Plasmodium (Plasmodium) coatneyi
Plasmodium (Plasmodium) cynomolgi
Plasmodium (Plasmodium) eylesi
Plasmodium (Plasmodium) fieldi
Plasmodium (Plasmodium) fragile
Plasmodium (Plasmodium) georgesi
Plasmodium (Plasmodium) girardi
Plasmodium (Plasmodium) gonderi
Plasmodium (Plasmodium) inui
Plasmodium (Plasmodium) jefferyi
Plasmodium (Plasmodium) joyeuxi
Plasmodium (Plasmodium) knowlei
Plasmodium (Plasmodium) hyobati
Plasmodium (Plasmodium) malariae
Plasmodium (Plasmodium) ovale
Plasmodium (Plasmodium) petersi
Plasmodium (Plasmodium) pitheci
Plasmodium (Plasmodium) rhodiani
Plasmodium (Plasmodium) schweitzi
Plasmodium (Plasmodium) semiovale
Plasmodium (Plasmodium) semnopitheci
Plasmodium (Plasmodium) silvaticum
Plasmodium (Plasmodium) simium
Plasmodium (Plasmodium) vivax
Plasmodium (Plasmodium) youngi
Plasmodium (Sauramoeba) achiotense
Plasmodium (Sauramoeba) adunyinkai
Plasmodium (Sauramoeba) aeuminatum
Plasmodium (Sauramoeba) agamae
Plasmodium (Sauramoeba) balli
Plasmodium (Sauramoeba) beltrani
Plasmodium (Sauramoeba) brumpti
Plasmodium (Sauramoeba) cnemidophori
Plasmodium (Sauramoeba) diploglossi
Plasmodium (Sauramoeba) giganteum
Plasmodium (Sauramoeba) heischi
Plasmodium (Sauramoeba) josephinae
Plasmodium (Sauramoeba) pelaezi
Plasmodium (Sauramoeba) zonuriae
Plasmodium (Vinckeia) achromaticum
Plasmodium (Vinckeia) aegyptensis
Plasmodium (Vinckeia) anomaluri
Plasmodium (Vinckeia) atheruri
Plasmodium (Vinckeia) berghei
Plasmodium (Vinckeia) booliati
Plasmodium (Vinckeia) brodeni
Plasmodium (Vinckeia) bubalis
Plasmodium (Vinckeia) bucki
Plasmodium (Vinckeia) caprae
Plasmodium (Vinckeia) cephalophi
Plasmodium (Vinckeia) chabaudi
Plasmodium (Vinckeia) coulangesi
Plasmodium (Vinckeia) cyclopsi
Plasmodium (Vinckeia) foleyi
Plasmodium (Vinckeia) girardi
Plasmodium (Vinckeia) incertae
Plasmodium (Vinckeia) inopinatum
Plasmodium (Vinckeia) landauae
Plasmodium (Vinckeia) lemuris
Plasmodium (Vinckeia) melanipherum
Plasmodium (Vinckeia) narayani
Plasmodium (Vinckeia) odocoilei
Plasmodium (Vinckeia) percygarnhami
Plasmodium (Vinckeia) pulmophilium
Plasmodium (Vinckeia) sandoshami
Plasmodium (Vinckeia) traguli
Plasmodium (Vinckeia) tyrio
Plasmodium (Vinckeia) uilenbergi
Plasmodium (Vinckeia) vinckei
Plasmodium (Vinckeia) watteni
Plasmodium (Vinckeia) yoelli
Host range
Host range among the mammalian orders is non uniform. At least 29
speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
infect non human primates; rodents outside the tropical parts of
AfricaAfrica is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area. With a billion people in 61 territories, it accounts for about 14.8% of the...
are rarely affected; a few species are known to infect
batBats are flying mammals in the order Chiroptera . The forelimbs of bats are webbed and developed as wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums and colugos, glide rather than...
s,
porcupine Porcupines are rodents with a coat of sharp spines, or quills, that defend them from predators. They are endemic in both the Old World and the New World. Porcupines are the third largest of the rodents, behind the capybara and the beaver. Most porcupines are about long, with an long tail....
s and
squirrelA squirrel is one of many small or medium-sized rodents in the family Sciuridae. In the English-speaking world, squirrel commonly refers to members of this family's genera Sciurus and Tamiasciurus, which are tree squirrels with large bushy tails, indigenous to Asia, the Americas and Europe....
s;
carnivoreA carnivore , meaning 'meat eater' , is an animal that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of vertebrate and/or invertebrate animal tissue, whether through predation or scavenging...
s,
insectivoreAn insectivore is a type of carnivore with a diet that consists chiefly of insects and similar small creatures.Although individually small, insects exist in enormous numbers and make up a very large part of the animal biomass in almost all non-marine environments...
s and
marsupialMarsupials are an infraclass of mammals, characterized by a distinctive pouch , in which females carry their young through early infancy.- History :...
s are not known to act as hosts.
The listing of host species among the reptiles has rarely been attempted. Ayala in 1978 listed 156 published accounts on 54 valid species and subspecies between 1909 and 1975. The regional breakdown was
AfricaAfrica is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area. With a billion people in 61 territories, it accounts for about 14.8% of the...
: 30 reports on 9 species;
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the continental mainland , the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans...
,
AsiaAsia is the world's largest and most populous continent, located in the eastern and northern hemispheres. It covers 8.6% of the earth's total surface area and with approximately 4 billion people, it hosts 60% of the world's current human population.Asia is traditionally defined as part of the...
&
OceaniaOceania is a geographical, often geopolitical, region consisting of numerous lands—mostly islands in the Pacific Ocean and vicinity. The term "Oceania" was coined in 1831 by French explorer Dumont d'Urville...
: 12 reports on 6 species and 2 subspecies;
AmericasThe Americas, or America, are lands in the Western hemisphere or New World, comprising the continents of North America and South America with their associated islands and regions. America may be ambiguous in English, as it is more commonly used to refer to the United States of America...
: 116 reports on 37 species.
Because of the number of species parasited by Plasmodium
further discussion has been broken down into following pages:
- Plasmodium species infecting birds
Species in five subgenera of Plasmodium infect birds - Bennettinia, Giovannolaia, Haemamoeba, Huffia and Novyella. Giovannolaia appears to be a polyphytic group and may be sudivided in the future.- Parasite listing :...
- Plasmodium species infecting reptiles
Over 90 species and subspecies of Plasmodium infect lizards. They have been reported from over 3200 species of lizard but only 29 species of snake. Three species - P. pessoai, P. tomodoni and P. wenyoni - infect snakes...
Species reclassified into other genera
The literature is replete with species initially classified as Plasmodium
that have been subsequently reclassified. With DNA taxonomy some of these may be once again be classified as Plasmodium
. Some of these species are listed here for completeness.
The following species are currently (2007) regarded as belonging to the genus Hepatocystis
rather than Plasmodium
:
Plasmodium epomophori
Plasmodium kochi
Plasmodium limnotragi
Van Denberghe 1937
Plasmodium pteropi
Breinl 1911
Plasmodium ratufae
Donavan 1920
Plasmodium vassali
Laveran 1905
The following species are now considered to belong to the genus Haemoemba
rather than to Plasmodium
:
Plasmodium praecox
Plasmodium rousseleti
The following species been reclassified as a species of Garnia
:
Plasmodium gonatodi
Host note: Hepatocystis epomophori
infects the batBats are flying mammals in the order Chiroptera . The forelimbs of bats are webbed and developed as wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums and colugos, glide rather than...
(Hypsignathus monstruosus
)
Species of dubious validity
The following species are currently regarded as questionable validity (nomen dubium
). While most of these 'species' have been reported in the literature it has in general been difficult to independently confirm their existence. Some of these may be reclassified into different taxa while others seem likely to be declared to be non species i.e. that a mistake was made by the authors. Until a ruling on these species has been made their status is likely to remain unclear.
Plasmodium bitis
Plasmodium bowiei
Plasmodium brucei
Plasmodium bufoni
Plasmodium caprea
Plasmodium carinii
Plasmodium causi
Plasmodium chalcidi
Plasmodium chloropsidis
Plasmodium centropi
Plasmodium danilweskyi
Plasmodium divergens
Plasmodium effusum
Plasmodium fabesia
Plasmodium gambeli
Plasmodium galinulae
Plasmodium herodiadis
Plasmodium limnotragi
Plasmodium malariae raupachi
Plasmodium moruony
Plasmodium periprocoti
Plasmodium ploceii
Plasmodium struthionis
Further reading
Standard reference books for the identification of Plasmodium species
-
- This book is the standard reference work on malarial species classification even if it a little dated now. A number of additional species have been described since its publication.
Other useful references
External links
Some history of malaria - http://muse.jhu.edu/journals/bulletin_of_the_history_of_medicine/v079/79.2slater.html