Dirofilaria repens
Encyclopedia
Dirofilaria repens is a filarial nematode
that affects dog
s and other carnivore
s such as cat
s, wolves
, coyote
s, fox
es, muskrat
s and sea lion
s. Although humans may become infected as aberrant hosts, the worms fail to reach adulthood while residing in a human body.
l stages in a vertebral host
and an arthropod
(mosquito
) intermediate host and vector
. In the first stage, mated adult female worms produce thousands of microfilaria
e (larvae) into the circulation
daily, which are ingested by mosquitoes in a blood
meal. Larvae develop into infective larvae within the mosquito over the next 10–16 days, depending on environmental conditions, before being reintroduced back into a new host. Microfilariae undergo secondary developmental changes in the insect. For the final two stages of development, third-stage larvae are inoculated back into a vertebral
host during an act of feeding. The adults of D. repens reside in the subcutaneous tissues of dogs and cats for the next several months before migrating to the heart, where they mature in 6–7 months. Adult worms are 1–2 mm in diameter (females are 25–30 cm in length, the males being shorter).
Humans are accidental hosts because adult worms can not reach maturity in the heart or in the skin. Most infective larvae introduced into humans are thought to die; therefore, infected individuals usually are not microfilaremic. Human disease is amicrofilaremic.
, which is caused by a macrofilaria that is trapped by the immune system. Subcutaneous migration of the worm may result in local swellings with changing localization. In addition, rare cases of organ manifestation have been reported, affecting the lung, male genitals, female breast or the eye. The latter is found in particular during the migratory phase of the parasite. D. repens occurs more commonly in adults (aged 40–49 years). The only exception is in Sri Lanka, where children younger than 9 years are most likely to be infected. The youngest individual reported was aged 4 months.
grounds is difficult, because a large number of zoonotic
Dirofilaria species have been described that share morphologic features with D. repens.
(DEC) if the syndrome is recognized prior to surgery. However, most cases are diagnosed retrospectively, when histopathological sections of biopsy or excision material are viewed. In term of surgical care, excision of lesions and affected areas is the treatment of choice for patients with human dirofilariasis. Some authors have recommended a period of observing chest coin lesions for several months if dirofilariasis is suspected and no other features in the history or examination suggesting malignancy or other infection are present. Also no specific diet is recommended for patients with dirofilariasis.
Filariasis
Filariasis is a parasitic disease and is considered an infectious tropical disease, that is caused by thread-like nematodes belonging to the superfamily Filarioidea, also known as "filariae"....
that affects dog
Dog
The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
s and other carnivore
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
s such as cat
Cat
The cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...
s, wolves
Gray Wolf
The gray wolf , also known as the wolf, is the largest extant wild member of the Canidae family...
, coyote
Coyote
The coyote , also known as the American jackal or the prairie wolf, is a species of canine found throughout North and Central America, ranging from Panama in the south, north through Mexico, the United States and Canada...
s, fox
Fox
Fox is a common name for many species of omnivorous mammals belonging to the Canidae family. Foxes are small to medium-sized canids , characterized by possessing a long narrow snout, and a bushy tail .Members of about 37 species are referred to as foxes, of which only 12 species actually belong to...
es, muskrat
Muskrat
The muskrat , the only species in genus Ondatra, is a medium-sized semi-aquatic rodent native to North America, and introduced in parts of Europe, Asia, and South America. The muskrat is found in wetlands and is a very successful animal over a wide range of climates and habitats...
s and sea lion
Sea Lion
Sea lions are pinnipeds characterized by external ear-flaps, long fore-flippers, the ability to walk on all fours, and short thick hair. Together with the fur seal, they comprise the family Otariidae, or eared seals. There are six extant and one extinct species in five genera...
s. Although humans may become infected as aberrant hosts, the worms fail to reach adulthood while residing in a human body.
Epidemiology
It most often found in the Mediterranean region, sub-Saharan Africa, and Eastern Europe. Italy bears the highest burden of European Dirofilariasis cases in humans: (66%), followed by France (22%), Greece (8%), and Spain (4%).Life Cycle
The life cycle of Diroflaria repens consists of five larvaLarva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
l stages in a vertebral host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
and an arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
(mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
) intermediate host and vector
Vector
Vector, a Latin word meaning "carrier", may refer in English to:-In computer science:*A one-dimensional array**Vector , a data type in the C++ Standard Template Library...
. In the first stage, mated adult female worms produce thousands of microfilaria
Microfilaria
The microfilaria is a stage in the life cycle of certain parasitic nematodes in the family Onchocercidae. In these species, the adults live in the circulatory system of vertebrates while the early larval stages develop in blood-feeding arthropod vectors...
e (larvae) into the circulation
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...
daily, which are ingested by mosquitoes in a blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
meal. Larvae develop into infective larvae within the mosquito over the next 10–16 days, depending on environmental conditions, before being reintroduced back into a new host. Microfilariae undergo secondary developmental changes in the insect. For the final two stages of development, third-stage larvae are inoculated back into a vertebral
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
host during an act of feeding. The adults of D. repens reside in the subcutaneous tissues of dogs and cats for the next several months before migrating to the heart, where they mature in 6–7 months. Adult worms are 1–2 mm in diameter (females are 25–30 cm in length, the males being shorter).
Humans are accidental hosts because adult worms can not reach maturity in the heart or in the skin. Most infective larvae introduced into humans are thought to die; therefore, infected individuals usually are not microfilaremic. Human disease is amicrofilaremic.
Infections in Humans
Infections in humans usually manifests as a single subcutaneous noduleCutaneous conditions
There are many conditions of or affecting the human integumentary system—the organ system that comprises the entire surface of the body and includes skin, hair, nails, and related muscle and glands.- Diseases :...
, which is caused by a macrofilaria that is trapped by the immune system. Subcutaneous migration of the worm may result in local swellings with changing localization. In addition, rare cases of organ manifestation have been reported, affecting the lung, male genitals, female breast or the eye. The latter is found in particular during the migratory phase of the parasite. D. repens occurs more commonly in adults (aged 40–49 years). The only exception is in Sri Lanka, where children younger than 9 years are most likely to be infected. The youngest individual reported was aged 4 months.
Diagnosis
Final diagnosis is established by microscopic examination of the excised worm. Making a definite species diagnosis on morphologicMorphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
grounds is difficult, because a large number of zoonotic
Zoonosis
A zoonosis or zoonoseis any infectious disease that can be transmitted from non-human animals to humans or from humans to non-human animals . In a study of 1415 pathogens known to affect humans, 61% were zoonotic...
Dirofilaria species have been described that share morphologic features with D. repens.
Treatment
Antifilarial medication for infected humans generally is not supported in the medical literature. One group of authors has recommended a single dose of Ivermectin followed by 3 doses of diethylcarbamazineDiethylcarbamazine
Diethylcarbamazine is an anthelmintic drug that does not resemble other antiparasitic compounds. It is a synthetic organic compound which is highly specific for several parasites and does not contain any toxic metallic elements.-Uses:...
(DEC) if the syndrome is recognized prior to surgery. However, most cases are diagnosed retrospectively, when histopathological sections of biopsy or excision material are viewed. In term of surgical care, excision of lesions and affected areas is the treatment of choice for patients with human dirofilariasis. Some authors have recommended a period of observing chest coin lesions for several months if dirofilariasis is suspected and no other features in the history or examination suggesting malignancy or other infection are present. Also no specific diet is recommended for patients with dirofilariasis.