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West Nile virus

West Nile virus

Overview
West Nile virus is a virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

 of the family Flaviviridae
Flaviviridae
The Flaviviridae are a family of viruses that are primarily spread through arthropod vectors . The family gets its name from Yellow Fever virus, a type virus of Flaviviridae; flavus means yellow in Latin...

. Part of the Japanese encephalitis
Japanese Encephalitis
Japanese encephalitis —previously known as Japanese B encephalitis to distinguish it from von Economo's A encephalitis—is a disease caused by the mosquito-borne Japanese encephalitis virus. The Japanese encephalitis virus is a virus from the family Flaviviridae. Domestic pigs and wild birds are...

 (JE) antigenic complex of viruses, it is found in both tropical
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately  N and the Tropic of Capricorn in the southern hemisphere at  S; these latitudes correspond to the axial tilt of the Earth...

 and temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...

 regions. It mainly infects bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s, but is known to infect human
Human
Humans are the only living species in the Homo genus...

s, horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...

s, 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, 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, bat
Bat
Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed 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 fly,...

s, chipmunk
Chipmunk
Chipmunks are small striped squirrels native to North America and Asia. They are usually classed either as a single genus with three subgenera, or as three genera.-Etymology and taxonomy:...

s, skunk
Skunk
Skunks are mammals best known for their ability to secrete a liquid with a strong, foul odor. General appearance varies from species to species, from black-and-white to brown or cream colored. Skunks belong to the family Mephitidae and to the order Carnivora...

s, squirrel
Squirrel
Squirrels belong to a large family of small or medium-sized rodents called the Sciuridae. The family includes tree squirrels, ground squirrels, chipmunks, marmots , flying squirrels, and prairie dogs. Squirrels are indigenous to the Americas, Eurasia, and Africa and have been introduced to Australia...

s, domestic rabbit
Rabbit
Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world...

s, crow
Crow
Crows form the genus Corvus in the family Corvidae. Ranging in size from the relatively small pigeon-size jackdaws to the Common Raven of the Holarctic region and Thick-billed Raven of the highlands of Ethiopia, the 40 or so members of this genus occur on all temperate continents and several...

s, robins, crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...

s and alligator
Alligator
An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. There are two extant alligator species: the American alligator and the Chinese alligator ....

s. The main route of human infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

 is through the bite of an infected 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...

. Approximately 90% of West Nile Virus infections in humans are without any symptoms.

Image reconstructions and cryoelectron microscopy reveal a 45–50 nm virion covered with a relatively smooth protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 surface.
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Unanswered Questions
Encyclopedia
West Nile virus is a virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

 of the family Flaviviridae
Flaviviridae
The Flaviviridae are a family of viruses that are primarily spread through arthropod vectors . The family gets its name from Yellow Fever virus, a type virus of Flaviviridae; flavus means yellow in Latin...

. Part of the Japanese encephalitis
Japanese Encephalitis
Japanese encephalitis —previously known as Japanese B encephalitis to distinguish it from von Economo's A encephalitis—is a disease caused by the mosquito-borne Japanese encephalitis virus. The Japanese encephalitis virus is a virus from the family Flaviviridae. Domestic pigs and wild birds are...

 (JE) antigenic complex of viruses, it is found in both tropical
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately  N and the Tropic of Capricorn in the southern hemisphere at  S; these latitudes correspond to the axial tilt of the Earth...

 and temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...

 regions. It mainly infects bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s, but is known to infect human
Human
Humans are the only living species in the Homo genus...

s, horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...

s, 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, 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, bat
Bat
Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed 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 fly,...

s, chipmunk
Chipmunk
Chipmunks are small striped squirrels native to North America and Asia. They are usually classed either as a single genus with three subgenera, or as three genera.-Etymology and taxonomy:...

s, skunk
Skunk
Skunks are mammals best known for their ability to secrete a liquid with a strong, foul odor. General appearance varies from species to species, from black-and-white to brown or cream colored. Skunks belong to the family Mephitidae and to the order Carnivora...

s, squirrel
Squirrel
Squirrels belong to a large family of small or medium-sized rodents called the Sciuridae. The family includes tree squirrels, ground squirrels, chipmunks, marmots , flying squirrels, and prairie dogs. Squirrels are indigenous to the Americas, Eurasia, and Africa and have been introduced to Australia...

s, domestic rabbit
Rabbit
Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world...

s, crow
Crow
Crows form the genus Corvus in the family Corvidae. Ranging in size from the relatively small pigeon-size jackdaws to the Common Raven of the Holarctic region and Thick-billed Raven of the highlands of Ethiopia, the 40 or so members of this genus occur on all temperate continents and several...

s, robins, crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...

s and alligator
Alligator
An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. There are two extant alligator species: the American alligator and the Chinese alligator ....

s. The main route of human infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

 is through the bite of an infected 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...

. Approximately 90% of West Nile Virus infections in humans are without any symptoms.

Image reconstructions and cryoelectron microscopy reveal a 45–50 nm virion covered with a relatively smooth protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 surface. This structure is similar to the dengue fever
Dengue fever
Dengue fever , also known as breakbone fever, is an infectious tropical disease caused by the dengue virus. Symptoms include fever, headache, muscle and joint pains, and a characteristic skin rash that is similar to measles...

 virus; both belong to the genus Flavivirus within the family Flaviviridae. The genetic material of WNV is a positive-sense
Sense (molecular biology)
In molecular biology and genetics, sense is a concept used to compare the polarity of nucleic acid molecules, such as DNA or RNA, to other nucleic acid molecules...

, single strand of RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....

, which is between 11,000 and 12,000 nucleotide
Nucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...

s long; these genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...

 encode seven non-structural proteins and three structural proteins. The RNA strand is held within a nucleocapsid formed from 12 kDa
KDA
KDA may refer to:* Karachi Development Authority* Kongsberg Defence & Aerospace* Kotelawala Defence Academy* Kramer Design Associates* Lithium diisopropylamide, KDA is the potassium analogue of lithium diisopropylamideOr kDa may refer to:...

 protein blocks; the capsid is contained within a host-derived membrane
Biological membrane
A biological membrane or biomembrane is an enclosing or separatingmembrane that acts as a selective barrier, within or around a cell. It consists of a lipid bilayer with embedded proteins that may constitute close to 50% of membrane content...

 altered by two viral glycoprotein
Glycoprotein
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...

s.

Symptoms


The West Nile Virus produces one of three different outcomes in humans. The first is an asymptomatic
Asymptomatic
In medicine, a disease is considered asymptomatic if a patient is a carrier for a disease or infection but experiences no symptoms. A condition might be asymptomatic if it fails to show the noticeable symptoms with which it is usually associated. Asymptomatic infections are also called subclinical...

 infection; the second is a mild febrile
Fever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...

 syndrome termed West Nile Fever; the third is a neuroinvasive disease
Neurotropic virus
A neurotropic virus is a virus which is capable of infecting nerve cells, or which does so preferentially. Such viruses thereby largely evade the usual immune response—which acts only within the blood system.- Terminology :...

 termed West Nile meningitis
Meningitis
Meningitis is inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs...

 or encephalitis
Encephalitis
Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...

. The population proportion of these three states is roughly 110:30:1.

The second, febrile stage has an incubation period
Incubation period
Incubation period is the time elapsed between exposure to a pathogenic organism, a chemical or radiation, and when symptoms and signs are first apparent...

 of 2 to 8 days followed by fever, headache, chills, diaphoresis
Diaphoresis
Diaphoresis is excessive sweating commonly associated with shock and other medical emergency conditions.Diaphoretic is the state of perspiring profusely, or something that has the power to cause increased perspiration....

 (excessive sweating), weakness, lymphadenopathy
Lymphadenopathy
Lymphadenopathy is a term meaning "disease of the lymph nodes." It is, however, almost synonymously used with "swollen/enlarged lymph nodes". It could be due to infection, auto-immune disease, or malignancy....

 (swollen lymph nodes), drowsiness, pain in the joints and symptoms like those of influenza or the flu. Occasionally there is a short-lived truncal rash and some patients experience gastrointestinal symptoms including nausea, vomiting, loss of appetite, or diarrhea. Symptoms are generally resolved within 7 to 10 days, although fatigue can persist for some weeks and lymphadenopathy up to two months.

The more dangerous encephalitis is characterized by similar early symptoms but also a decreased level of consciousness, sometimes approaching near-coma
Coma
In medicine, a coma is a state of unconsciousness, lasting more than 6 hours in which a person cannot be awakened, fails to respond normally to painful stimuli, light or sound, lacks a normal sleep-wake cycle and does not initiate voluntary actions. A person in a state of coma is described as...

. Deep tendon reflexes are hyperactive at first, later diminished. There are also extrapyramidal disorders. Recovery is marked by a long convalescence
Convalescence
Convalescence is the gradual recovery and of health and strength after illness. It refers to the later stage of an infectious disease or illness when the patient recovers and returns to normal, but may continue to be a source of infection even if feeling better...

 with fatigue.

More recent outbreaks have resulted in a deeper study of the disease and other, rarer, outcomes have been identified. The spinal cord may be infected, marked by anterior myelitis with or without encephalitis. WNV-associated Guillain-Barré syndrome
Guillain-Barré syndrome
Guillain–Barré syndrome , sometimes called Landry's paralysis, is an acute inflammatory demyelinating polyneuropathy , a disorder affecting the peripheral nervous system. Ascending paralysis, weakness beginning in the feet and hands and migrating towards the trunk, is the most typical symptom...

 has been identified and other rare effects include multifocal chorioretinitis
Chorioretinitis
Chorioretinitis is an inflammation of the choroid and retina of the eye. It is also known as choroid retinitis.-Causes:...

 (which has 100% specificity for identifying WNV infection in patients with possible WNV encephalitis), hepatitis
Hepatitis
Hepatitis is a medical condition defined by the inflammation of the liver and characterized by the presence of inflammatory cells in the tissue of the organ. The name is from the Greek hepar , the root being hepat- , meaning liver, and suffix -itis, meaning "inflammation"...

, myocarditis
Myocarditis
Myocarditis is inflammation of heart muscle . It resembles a heart attack but coronary arteries are not blocked.Myocarditis is most often due to infection by common viruses, such as parvovirus B19, less commonly non-viral pathogens such as Borrelia burgdorferi or Trypanosoma cruzi, or as a...

, nephritis
Nephritis
Nephritis is inflammation of the nephrons in the kidneys. The word "nephritis" was imported from Latin, which took it from Greek: νεφρίτιδα. The word comes from the Greek νεφρός - nephro- meaning "of the kidney" and -itis meaning "inflammation"....

, pancreatitis
Pancreatitis
Pancreatitis is inflammation of the pancreas. It occurs when pancreatic enzymes that digest food are activated in the pancreas instead of the small intestine. It may be acute – beginning suddenly and lasting a few days, or chronic – occurring over many years...

, and splenomegaly
Splenomegaly
Splenomegaly is an enlargement of the spleen. The spleen usually lies in the left upper quadrant of the human abdomen. It is one of the four cardinal signs of hypersplenism, some reduction in the number of circulating blood cells affecting granulocytes, erythrocytes or platelets in any...

.

Mortality rate


There is no way to accurately measure the number of worldwide cases at this time. However, the United States keeps records of West Nile infection cases. In 2009, there were 663 cases. Three hundred thirty-five of these cases were encephalitis or meningitis infections, a reaction to the virus that approximately 1 in 150 people who get the virus will show. Three hundred two cases were filed for West Nile fever, the most likely symptom of the virus. Twenty six cases were unspecified. The state of Texas had the most cases, with 104 total. The total mortality rate for 2009 was 30 deaths of the 663 reported serious cases. That is a 4.5% casualty rate, but only of the severe infections. Approximately 80% of cases have no symptoms, and therefore the total casualty rate would be less than 1% of total infections in the U.S. This data and earlier years data is available from the Centers for Disease Control and Prevention
Centers for Disease Control and Prevention
The Centers for Disease Control and Prevention are a United States federal agency under the Department of Health and Human Services headquartered in Druid Hills, unincorporated DeKalb County, Georgia, in Greater Atlanta...

 (CDC).

Transmission



The virus is transmitted through mosquito vectors, which bite and infect birds. The birds are amplifying hosts, developing sufficient viral levels to transmit the infection to other biting mosquitoes which go on to infect other birds (in the Western hemisphere
Western Hemisphere
The Western Hemisphere or western hemisphere is mainly used as a geographical term for the half of the Earth that lies west of the Prime Meridian and east of the Antimeridian , the other half being called the Eastern Hemisphere.In this sense, the western hemisphere consists of the western portions...

 the American robin
American Robin
The American Robin or North American Robin is a migratory songbird of the thrush family. It is named after the European Robin because of its reddish-orange breast, though the two species are not closely related, with the European robin belonging to the flycatcher family...

 and the American crow
American Crow
The American Crow is a large passerine bird species of the family Corvidae. It is a common bird found throughout much of North America...

 are the most common carriers) and also humans. The infected mosquito species vary according to geographical area; in the US Culex pipiens
Culex pipiens
Culex pipiens is a species of blood-feeding mosquito of the family Culicidae. It is a vector of some diseases, such as Japanese encephalitis, meningitis, Urticaria...

(Eastern US), Culex tarsalis (Midwest and West), and Culex quinquefasciatus
Culex quinquefasciatus
Culex quinquefasciatus is the vector oflymphatic filariasis caused by the nematode Wuchereria bancroftiin the tropics and sub tropics.-Primary vector of Lymphatic Filariasis in India:...

(Southeast) are the main sources.

In mammals the virus does not multiply as readily (i.e. does not develop high viremia
Viremia
Viremia is a medical condition where viruses enter the bloodstream and hence have access to the rest of the body. It is similar to bacteremia, a condition where bacteria enter the bloodstream.- Primary versus Secondary :...

 during infection), and it is believed that mosquitoes biting infected mammals do not ingest sufficient virus to become infected, making mammals so-called dead-end infections.

A 2004 paper in Science found that Culex pipiens mosquitoes existed in two populations in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, one which bites birds and one which bites humans. In North America 40% of Culex pipiens were found to be hybrids of the two types which bite both birds and humans, providing a vector for WNV. This is argued to provide an explanation of why the West Nile disease has spread more quickly in North America than Europe. However, these conclusions have been disputed. In 2010 it was verified by the Greek Center for Disease Control and Prevention that Culex pipiens was responsible for an outbreak of the virus in northern Greece.

Susceptibility


It was initially believed that direct human-to-human transmission was only caused by occupational exposure, or conjunctival exposure to infected blood. The US outbreak revealed novel transmission methods, through blood transfusion, organ transplant, intrauterine exposure, and breast feeding. Since 2003, blood banks in the US routinely screen for the virus amongst their donors. As a precautionary measure, the UK's National Blood Service
National Blood Service
The National Blood Service is the organisation for England and North Wales which collects blood and other tissues, tests, processes, and supplies all the hospitals in England and North Wales...

 initially ran a test for this disease in donors who donate within 28 days of a visit to the United States, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

 or the North Eastern provinces of Italy. Currently (September 2011) the policy of the National Blood Service is as follows:

"In the last year there have been significant outbreaks in mainland Greece, Romania, Albania, Israel and in the south west of the Russian Federation just north of the Black and Caspian seas. In recent years North Eastern Italy in the provincial districts of Ferrara, Rovigo, Mantua, Modena, Bologna and Reggio Emilia (an area north of Rimini and east of Parma) have also been affected.
Donors who have visited a WNV endemic area between April 1st and November 30th may donate blood four weeks after their return, as long as they have had neither symptoms nor evidence of infection. If the donor was diagnosed with WNV, or had a history of symptoms suggestive of WNV, whilst in the endemic area or following their return then they must wait 6 months before donating."

The Scottish National Blood Transfusion Service
Scottish National Blood Transfusion Service
The Scottish National Blood Transfusion Service is the national blood, blood product and tissue provider of Scotland. It is a special health board of the Scottish National Health Service.-History:...

 is to ask prospective donors to wait 28 days after returning from North America or the North Eastern provinces of Italy before donating.

The more severe outcomes of WNV infection are clearly associated with advancing age and a patient history of organ transplantation and diabetes. A genetic factor also appears to increase susceptibility to West Nile disease. A mutation of the gene CCR5
CCR5
C-C chemokine receptor type 5, also known as CCR5, is a protein that in humans is encoded by the CCR5 gene. CCR5 is a member of the beta chemokine receptors family of integral membrane proteins...

 gives some protection against HIV
HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...

 but leads to more serious complications of WNV infection. Carriers of two mutated copies of CCR5 made up 4 to 4.5% of a sample of West Nile disease sufferers while the incidence of the gene in the general population is only 1%.

Recently, the potential for mosquito saliva to impact the course of WNV disease was demonstrated. Mosquitoes inoculate their saliva into the skin while obtaining blood. Mosquito saliva is a pharmacologic cocktail of secreted molecules, principally proteins, that can affect vascular constriction, blood coagulation, platelet aggregation, inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...

, and immunity
Immunity (medical)
Immunity is a biological term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion. Immunity involves both specific and non-specific components. The non-specific components act either as barriers or as eliminators of wide...

. It has become clear that mosquito saliva alters the immune response in a manner that may be advantageous to a virus. Studies have shown that it can specifically modulate the immune response during early virus infection, and mosquito feeding can exacerbate WNV infection leading to higher viremia
Viremia
Viremia is a medical condition where viruses enter the bloodstream and hence have access to the rest of the body. It is similar to bacteremia, a condition where bacteria enter the bloodstream.- Primary versus Secondary :...

 and more severe forms of disease. It is unknown what benefit, if any, the mosquito receives by assisting the virus in this manner, so it is likely that the virus is simply exploiting the preexisting qualities of mosquito saliva developed for other purposes.

There is no vaccine
Vaccine
A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...

 for humans. A vaccine for horses (ATCvet code: ) based on killed viruses exists; some zoo
Zoo
A zoological garden, zoological park, menagerie, or zoo is a facility in which animals are confined within enclosures, displayed to the public, and in which they may also be bred....

s have given this vaccine to their birds, although its effectiveness there is unknown. Dogs and cats show few if any signs of infection. There have been no known cases of direct canine-human or feline-human transmission; although these pets can become infected, it is unlikely that they are in turn capable of infecting native mosquitoes and thus continuing the disease cycle.

Avoiding mosquito bites is the most straightforward means to avoid infection—remaining indoors (while preventing mosquitoes from entering) at dawn and dusk, wear light-colored clothing that covers arms and legs as well as trunk, use insect repellents on both skin and clothing (such as DEET
DEET
N,N-Diethyl-meta-toluamide, abbreviated DEET, is a slightly yellow oil. It is the most common active ingredient in insect repellents...

, picaradin, or oil of lemon eucalyptus for skin and permethrin
Permethrin
Permethrin is a common synthetic chemical, widely used as an insecticide, acaricide, and insect repellent. It belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation. It is not known to...

 for clothes). If one becomes infected, generally, treatment is purely supportive: analgesia for the pain of neurologic diseases; rehydration for nausea, vomiting, or diarrhea; encephalitis may also require airway protection and seizure management.

Reported cases in the U.S. in 2005 exceeded those in 2004, and cases in 2006 exceeded 2005's totals. On August 19, 2006, the LA Times reported that the expected incidence rate of WNV was dropping as the local population becomes exposed to the virus. "In countries like Egypt and Uganda, where West Nile was first detected, people became fully immune to the virus by the time they reached adulthood", federal health officials said. However, just days later, the CDC said that WNV cases could reach a three-year high because hot temperatures had allowed a larger brood of mosquitoes.

History


Studies of phylogenetic lineages have determined that WNV emerged as a distinct virus around 1000 years ago. This initial virus developed into two distinct lineages, Lineage 1 and its multiple profiles is the source of the epidemic transmission in Africa and throughout the world. Lineage 2 was considered an Africa zoonose. However, in 2008, lineage 2, previously only seen in horses in sub-Saharan Africa and Madagascar, began to appear in horses in Europe, where the first known outbreak affected 18 animals in Hungary in 2008. Lineage 1 West Nile virus was detected in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

 in 2010 in a mare
Mare
Female horses are called mares.Mare is the Latin word for "sea".The word may also refer to:-People:* Ahmed Marzooq, also known as Mare, a footballer and Secretary General of Maldives Olympic Committee* Mare Winningham, American actress and singer...

 and her aborted fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...

; previously, only lineage 2 West Nile virus had been detected in horses and humans in South Africa. A 2007 fatal case in a killer whale in Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

 broadened the known host range of West Nile virus to include cetaceans.

WNV has been posited as one of the possible causes of Alexander the Great's early death based on reports of avian deaths before his illness period.

WNV was first isolated from a feverish 37 year old woman at Omogo in the West Nile District
West Nile sub-region
West Nile sub-region is a region in north-western Uganda that consists of the districts of Adjumani, Arua, Koboko, Maracha-Terego, Moyo, Nebbi and Yumbe...

 of Uganda
Uganda
Uganda , officially the Republic of Uganda, is a landlocked country in East Africa. Uganda is also known as the "Pearl of Africa". It is bordered on the east by Kenya, on the north by South Sudan, on the west by the Democratic Republic of the Congo, on the southwest by Rwanda, and on the south by...

 in 1937 during research on yellow fever virus. A series of serosurveys in 1939 in central Africa found anti-WNV positive results ranging from 1.4% (Congo) to 46.4% (White Nile region, Sudan). It was subsequently identified in Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

 (1942) and India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

 (1953), a 1950 serosurvey in Egypt found 90% of those over 40 years in age had WNV antibodies. The ecology was characterized in 1953 with studies in Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

 and Israel
Israel
The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...

. The virus became recognized as a cause of severe human meningoencephalitis
Meningoencephalitis
Meningoencephalitis is a medical condition that simultaneously resembles both meningitis, which is an infection or inflammation of the meninges, and encephalitis, which is an infection or inflammation of the brain.-Causes:...

 in elderly patients during an outbreak in Israel in 1957. The disease was first noted in horses in Egypt and France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 in the early 1960s and found to be widespread in southern Europe, southwest Asia and Australia.

The first appearance of WNV in the Western hemisphere was in 1999 with encephalitis reported in humans, dogs, cats, and horses, and the subsequent spread in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 may be an important milestone in the evolving history of this virus. The American outbreak began in the New York City
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...

 area (specifically, College Point, Queens
College Point, Queens
College Point is a working-middle class neighborhood in the New York City borough of Queens. It is located north of Flushing on Flushing Bay and the East River and is part of the Queens Community Board 7. Willets Point Boulevard and the Whitestone Expressway are often the neighborhood's...

) and was later seen in New Jersey
New Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...

 and Connecticut
Connecticut
Connecticut is a state in the New England region of the northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, and the state of New York to the west and the south .Connecticut is named for the Connecticut River, the major U.S. river that approximately...

; the virus is believed to have entered in an infected bird or mosquito, although there is no clear evidence. The US virus was very closely related to a lineage 1 strain found in Israel in 1998. Since the first North American cases in 1999, the virus has been reported throughout the United States, Canada, Mexico, the Caribbean and Central America. There have been human cases and equine cases, and many birds are infected. The Barbary Macaque
Barbary Macaque
The Barbary Macaque , or Common macaque, is a macaque with no tail. Found in the Atlas Mountains of Algeria and Morocco with a small population, of unknown origin, in Gibraltar, the Barbary Macaque is one of the best-known Old World monkey species. Besides humans, they are the only primates that...

, Macaca sylvanus, was the first non-human primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...

 to contract WNV. Both the US and Israeli strains are marked by high mortality rates in infected avian populations; the presence of dead birds—especially corvidae
Corvidae
Corvidae is a cosmopolitan family of oscine passerine birds that contains the crows, ravens, rooks, jackdaws, jays, magpies, treepies, choughs and nutcrackers. The common English names used are corvids or the crow family , and there are over 120 species...

—can be an early indicator of the arrival of the virus.

A high level of media coverage through 2001/2002 raised public awareness of WNV. This coverage was most likely the result of successive appearances of the virus in new areas, and had the unintended effect of increasing funding for research on this virus and related 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...

-borne viruses. Such research has expanded our understanding of viruses transmitted by mosquitoes.

Overwintering mechanism


Vertical transmission
Vertical transmission
Vertical transmission, also known as mother-to-child transmission, is the transmission of an infection or other disease from mother to child immediately before and after birth during the perinatal period. A pathogen's transmissibility refers to its capacity for vertical transmission...

 of West Nile Virus from female Culex pipiens mosquitoes to their progeny has been demonstrated in the laboratory. It has not been suggested that vertically infected Culex could survive the winter to initiate a WNV amplification cycle the following spring. Culex mosquitoes spend the winter hibernating in protected structures such as root cellars, bank barns, caves, abandoned tunnels and other subterranean locations. The first overwintering adult mosquitoes to test positive for WNV were collected in New York, 2000. Since then, positive samples have been identified in New Jersey, 2003 and in Pennsylvania, 2003, 2004 and 2005.

Geographic distribution


West Nile virus has been described in Africa
Africa
Africa 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...

, Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, the Middle East
Middle East
The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...

, west and central Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

, Oceania
Oceania
Oceania is a region centered on the islands of the tropical Pacific Ocean. Conceptions of what constitutes Oceania range from the coral atolls and volcanic islands of the South Pacific to the entire insular region between Asia and the Americas, including Australasia and the Malay Archipelago...

 (subtype Kunjin
Kunjin virus
Kunjin virus is a zoonotic virus of the family Flaviviridae and the genus Flavivirus. It is a subtype of West Nile Virus endemic to Oceania.-History:...

), and most recently, North America.

Recent outbreaks of West Nile virus encephalitis in humans have occurred in Algeria
Algeria
Algeria , officially the People's Democratic Republic of Algeria , also formally referred to as the Democratic and Popular Republic of Algeria, is a country in the Maghreb region of Northwest Africa with Algiers as its capital.In terms of land area, it is the largest country in Africa and the Arab...

 (1994), Romania
Romania
Romania is a country located at the crossroads of Central and Southeastern Europe, on the Lower Danube, within and outside the Carpathian arch, bordering on the Black Sea...

 (1996 to 1997), the Czech Republic
Czech Republic
The Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....

 (1997), Congo
Democratic Republic of the Congo
The Democratic Republic of the Congo is a state located in Central Africa. It is the second largest country in Africa by area and the eleventh largest in the world...

 (1998), Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

 (1999), the United States (1999 to 2009), Canada (1999–2007), Israel
Israel
The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...

 (2000) and Greece
Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....

 (2010).

Epizootic
Epizootic
In epizoology, an epizootic is a disease that appears as new cases in a given animal population, during a given period, at a rate that substantially exceeds what is "expected" based on recent experience . Epidemic is the analogous term applied to human populations...

s of disease in horses occurred in Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...

 (1996), Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

 (1998), the United States (1999 to 2001), and France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 (2000). In 2003, West Nile virus was found in horses in Mexico.
In 2011, West Nile Virus was found in horses in Sardinia (Italy).

In the US in 2008, West Nile virus was reported in animals in 47 states, D.C. and Puerto Rico. 45 states and D.C. reported human cases in 2008 with only Maine, Alaska and Hawaii having never had a human case. (Maine has had occasional animal cases.)

Recent outbreaks



United States: From 1999 through 2001, the CDC
Centers for Disease Control and Prevention
The Centers for Disease Control and Prevention are a United States federal agency under the Department of Health and Human Services headquartered in Druid Hills, unincorporated DeKalb County, Georgia, in Greater Atlanta...

 confirmed 149 West Nile virus infections, including 18 deaths. In 2002, a total of 4,156 cases were reported, including 284 fatalities. 13 cases in 2002 were contracted through blood transfusion. The cost of WNV-related health care in 2002 was estimated at $200 million. The first human West Nile disease in 2003 occurred in June and one West Nile-infected blood transfusion was also identified that month. In the 2003 outbreak, 9,862 cases and 264 deaths were reported by the CDC. At least 30% of those cases were considered severe involving meningitis or encephalitis. In 2004, there were only 2,539 reported cases and 100 deaths. In 2005, there was a slight increase in the number of cases, with 3,000 cases and 119 deaths reported. 2006 saw another increase, with 4,269 cases and 177 deaths. In 2007, the number of cases reported decreased to 3,623 and the number of deaths dropped to 124. In 2007, 1,227 cases of wnv neuroinvasion disease and 117 deaths occurred. In 2008, West Nile surveillance data reported to CDC, a total of 28 states have reported 236 cases of human WNV illness. A total of 137 cases for which such data were available occurred in males, median age patients was 48 years. Dates of illness onset ranged from January 17 to August 14: Two cases were fatal.

Canada: One human death occurred in 1999. In 2002, ten human deaths out of 416 confirmed and probable cases were reported by Canadian health officials. In 2003, 14 deaths and 1,494 confirmed and probable cases were reported. Cases were reported in 2003 in Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...

, Quebec
Quebec
Quebec or is a province in east-central Canada. It is the only Canadian province with a predominantly French-speaking population and the only one whose sole official language is French at the provincial level....

, Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....

, Manitoba
Manitoba
Manitoba is a Canadian prairie province with an area of . The province has over 110,000 lakes and has a largely continental climate because of its flat topography. Agriculture, mostly concentrated in the fertile southern and western parts of the province, is vital to the province's economy; other...

, Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....

, Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...

, British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

, and the Yukon
Yukon
Yukon is the westernmost and smallest of Canada's three federal territories. It was named after the Yukon River. The word Yukon means "Great River" in Gwich’in....

. In 2004, only 26 cases were reported and two deaths; however, 2005 saw 239 cases and 12 deaths. By October 28, 2006, 127 cases and no deaths had been reported. One case was asymptomatic and only discovered through a blood donation. In 2007, 445 Manitobans had confirmed cases of WNV and two people died with a third unconfirmed but suspected. 17 people have either tested positive or are suspected of having the virus in Saskatchewan, and only one person has tested positive in Alberta.
Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....

 has reported 826 cases of WNV plus three deaths. The spread of West Nile Virus infected mosquitoes to British Columbia for the first time was reported in 2009

Israel: In the year 2000, the CDC
Centers for Disease Control and Prevention
The Centers for Disease Control and Prevention are a United States federal agency under the Department of Health and Human Services headquartered in Druid Hills, unincorporated DeKalb County, Georgia, in Greater Atlanta...

 found that there were 417 confirmed cases with 326 hospitalizations. 33 of these people died. The main clinical presentations were encephalitis (57.9%), febrile disease (24.4%), and meningitis (15.9%).

Romania: In 1996–1997 about 500 cases occurred in Romania with a fatality rate of nearly 10%. In 2010 there were 34 confirmed cases and 3 fatalities.

Greece: In the summer of 2010 several cases were reported in northern Greece. In total there were 261 diagnosed cases and 34 fatalities.

Surveillance methods


West Nile virus can be sampled from the environment by the pooling of trapped mosquitoes, testing avian blood samples drawn from wild birds and dogs and sentinel monkeys, as well as testing brains of dead birds found by various animal control agencies and the public. Testing of the mosquito samples requires the use of RT-PCR to directly amplify and show the presence of virus in the submitted samples. When using the blood sera of wild bird and sentinel chickens, samples must be tested for the presence of WNV antibodies by use of immunohistochemistry
Immunohistochemistry
Immunohistochemistry or IHC refers to the process of detecting antigens in cells of a tissue section by exploiting the principle of antibodies binding specifically to antigens in biological tissues. IHC takes its name from the roots "immuno," in reference to antibodies used in the procedure, and...

 (IHC) or Enzyme-Linked Immunosorbent Assay (ELISA).

Dead birds, after necropsy, have their various tissues tested for virus by either RT-PCR or immunohistochemistry, where virus shows up as brown stained tissue because of a substrate-enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 reaction.

Control



West Nile control is achieved through mosquito control
Mosquito control
Mosquito control manages the population of mosquitoes to reduce their damage to human health, economies, and enjoyment. Mosquito control is a vital public-health practice throughout the world and especially in the tropics because mosquitoes spread many diseases, such as malaria.Mosquito-control...

, by elimination of mosquito breeding sites, larviciding active breeding areas and encouraging personal use of mosquito repellents. The public is also encouraged to spend less time outdoors, wear long covering clothing, apply bug repellant that contains DEET
DEET
N,N-Diethyl-meta-toluamide, abbreviated DEET, is a slightly yellow oil. It is the most common active ingredient in insect repellents...

 and ensure that mosquitoes cannot enter buildings.
Environmentalist
Environmentalist
An environmentalist broadly supports the goals of the environmental movement, "a political and ethical movement that seeks to improve and protect the quality of the natural environment through changes to environmentally harmful human activities"...

s have condemned attempts to control the transmitting mosquitoes by spraying pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...

, saying that the detrimental health effects of spraying outweigh the relatively few lives which may be saved, and that there are more environmentally friendly ways of controlling mosquitoes. They also question the effectiveness of insecticide spraying, as they believe mosquitoes that are resting or flying above the level of spraying will not be killed; the most common vector in the northeastern U.S., Culex pipiens, is a canopy
Canopy (forest)
In biology, the canopy is the aboveground portion of a plant community or crop, formed by plant crowns.For forests, canopy also refers to the upper layer or habitat zone, formed by mature tree crowns and including other biological organisms .Sometimes the term canopy is used to refer to the extent...

 feeder.

The first effective horse vaccine, West Nile-INNOVATOR was introduced by Fort Dodge Animal Health (Wyeth
Wyeth
Wyeth, formerly one of the companies owned by American Home Products Corporation , was a pharmaceutical company. The company was based in Madison, New Jersey, USA...

). Shortly thereafter, a second, one-annual-dose vaccine called Prevenile was introduced by Intervet/Schering-Plough Animal Health (Merck
Merck & Co.
Merck & Co., Inc. , also known as Merck Sharp & Dohme or MSD outside the United States and Canada, is one of the largest pharmaceutical companies in the world. The Merck headquarters is located in Whitehouse Station, New Jersey, an unincorporated area in Readington Township...

), followed by a DNA-based vaccine, called Recombitek (Merial
Merial
Merial is a multinational animal health company. It was formed as a joint venture between Merck & Co. and Sanofi-Aventis in 1997. Merial is now the animal health subsidiary of Sanofi-Aventis. Merial is a company leader in innovation, and provides an ample range with products to improve the...

). In 2009, a new killed virus vaccine was introduced by Boehringer-Ingelheim, a privately held pharmaceutical company, incorporating an equine origin WNV strain (E159), representative of the more recent WNV strains impacting horses.

Treatment research


AMD3100, which had been proposed as an antiretroviral drug for HIV, has shown promise against West Nile encephalitis. Morpholino
Morpholino
In molecular biology, a Morpholino is a molecule in a particular structural family that is used to modify gene expression. Morpholino oligomers are an antisense technology used to block access of other molecules to specific sequences within nucleic acid...

 antisense oligos conjugated to cell penetrating peptide
Cell penetrating peptide
Cell-penetrating peptides are short peptides that facilitate cellular uptake of various molecular cargo . The "cargo" is associated with the peptides either through chemical linkage via covalent bonds or through non-covalent interactions...

s have been shown to partially protect mice from WNV disease. There have also been attempts to treat infections using ribavirin
Ribavirin
Ribavirin is an anti-viral drug indicated for severe RSV infection , hepatitis C infection and other viral infections. Ribavirin is a prodrug, which when metabolised resembles purine RNA nucleotides...

, intravenous immunoglobulin, or alpha interferon. GenoMed, a U.S. biotech company, has found that blocking angiotensin II can treat the "cytokine storm
Cytokine storm
A cytokine storm, or hypercytokinemia is a potentially fatal immune reaction consisting of a positive feedback loop between cytokines and immune cells, with highly elevated levels of various cytokines.-Symptoms:...

" of West Nile virus encephalitis as well as other viruses.

In 2007 the World Community Grid
World Community Grid
World Community Grid is an effort to create the world's largest public computing grid to tackle scientific research projects that benefit humanity...

 launched the Discovering Dengue Drugs – Together
Discovering Dengue Drugs – Together
Discovering Dengue Drugs – Together is a World Community Grid project sponsored by scientists at the University of Texas Medical Branch at Galveston and the University of Chicago. Its goal is to identify new antiviral drugs effective against viruses from the family flaviviridae...

 project. This uses a distributed network of volunteers' computers via the Berkeley Open Infrastructure for Network Computing
Berkeley Open Infrastructure for Network Computing
The Berkeley Open Infrastructure for Network Computing is an open source middleware system for volunteer and grid computing. It was originally developed to support the SETI@home project before it became useful as a platform for other distributed applications in areas as diverse as mathematics,...

 (BOINC) to perform computer simulations of interacting molecules. Thousands of small molecules are screened for potential anti-viral properties with respect to West Nile and related viruses.

External links