West Nile virus
|West Nile fever|
|Classification and external resources|
West Nile virus (WNV) is a mosquito-borne zoonotic arbovirus belonging to the genus Flavivirus in the family Flaviviridae. This flavivirus is found in temperate and tropical regions of the world. It was first identified in the West Nile subregion in the East African nation of Uganda in 1937. Prior to the mid-1990s, WNV disease occurred only sporadically and was considered a minor risk for humans, until an outbreak in Algeria in 1994, with cases of WNV-caused encephalitis, and the first large outbreak in Romania in 1996, with a high number of cases with neuroinvasive disease. WNV has now spread globally, with the first case in the Western Hemisphere being identified in New York City in 1999; over the next 5 years, the virus spread across the continental United States, north into Canada, and southward into the Caribbean Islands and Latin America. WNV also spread to Europe, beyond the Mediterranean Basin, and a new strain of the virus was identified in Italy in 2012. WNV is now considered to be an endemic pathogen in Africa, Asia, Australia, the Middle East, Europe and in the United States, which in 2012 has experienced one of its worst epidemics. In 2012, WNV killed 286 people in the United States, with the state of Texas being hard hit by this virus, making the year the deadliest on record for the United States.
The main mode of WNV transmission is via various species of mosquitoes, which are the prime vector, with birds being the most commonly infected animal and serving as the prime reservoir host—especially passerines, which are of the largest order of birds, Passeriformes. WNV has been found in various species of ticks, but current research suggests they are not important vectors of the virus. WNV also infects various mammal species, including humans, and has been identified in reptilian species, including alligators and crocodiles, and also in amphibians. Not all animal species that are susceptible to WNV infection, including humans, and not all bird species develop sufficient viral levels to transmit the disease to uninfected mosquitoes, and are thus not considered major factors in WNV transmission.
Approximately 80% of West Nile virus infections in humans are subclinical, which cause no symptoms. In the cases where symptoms do occur—termed West Nile fever in cases without neurological disease—the time from infection to the appearance of symptoms (incubation period) is typically between 2 and 15 days. Symptoms may include fever, headaches, fatigue, muscle pain or aches, malaise, nausea, anorexia, vomiting, myalgias and rash. Less than 1% of the cases are severe and result in neurological disease when the central nervous system is affected. People of advanced age, the very young, or those with immunosuppression, either medically induced, such as those taking immunosupressive drugs, or due to a pre-existing medical condition such as HIV infection, are most susceptible. The specific neurological diseases that may occur are West Nile encephalitis, which causes inflammation of the brain, West Nile meningitis, which causes inflammation of the meninges, which are the protective membranes that cover the brain and spinal cord, West Nile meningoencephalitis, which causes inflammation of the brain and also the meninges surrounding it, and West Nile poliomyelitis—spinal cord inflammation, which results in a syndrome similar to polio, which may cause acute flaccid paralysis.
Currently, no vaccine against WNV infection is available. The best method to reduce the rates of WNV infection is mosquito control on the part of municipalities, businesses and individual citizens to reduce breeding populations of mosquitoes in public, commercial and private areas via various means including eliminating standing pools of water where mosquitoes breed, such as in old tires, buckets, unused swimming pools, etc. On an individual basis, the use of personal protective measures to avoid being bitten by an infected mosquito, via the use of mosquito repellent, window screens, avoiding areas where mosquitoes are more prone to congregate, such as near marshes, areas with heavy vegetation etc., and being more vigilant from dusk to dawn when mosquitoes are most active offers the best defense. In the event of being bitten by an infected mosquito, familiarity of the symptoms of WNV on the part of laypersons, physicians and allied health professionals affords the best chance of receiving timely medical treatment, which may aid in reducing associated possible complications and also appropriate palliative care.
Signs and symptoms
The incubation period for WNV—the amount of time from infection to symptom onset—is typically from between 2 and 15 days. Headache can be a prominent symptom of WNV fever, meningitis, encephalitis, meningoencephalitis, and it may or may not be present in poliomyelytis-like syndrome. Thus, headache is not a useful indicator of neuroinvasive disease.(CDC)
- West Nile fever (WNF), which occurs in 20 percent of cases, is a febrile syndrome that causes flu-like symptoms. Most characterizations of WNF generally describe it as a mild, acute syndrome lasting 3 to 6 days after symptom onset. Systematic follow-up studies of patients with WNF have not been done, so this information is largely anecdotal. In addition to a high fever, headache, chills, excessive sweating, weakness, fatigue, swollen lymph nodes, drowsiness, pain in the joints and flu-like symptoms. Gastrointestinal symptoms that may occur include nausea, vomiting, loss of appetite, and diarrhea. Fewer than one-third of patients develop a rash.
- West Nile neuroinvasive disease (WNND), which occurs in less than 1 percent of cases, is when the virus infects the central nervous system resulting in meningitis, encephalitis, meningoencephalitis or a poliomyelitis-like syndrome. Many patients with WNND have normal neuroimaging studies, although abnormalities may be present in various cerebral areas including the basal ganglia, thalamus, cerebellum, and brainstem.
- West Nile virus encephalitis (WNE) is the most common neuroinvasive manifestation of WNND. WNE presents with similar symptoms to other viral encephalitis with fever, headaches, and altered mental status. A prominent finding in WNE is muscular weakness (30 to 50 percent of patients with encephalitis), often with lower motor neuron symptoms, flaccid paralysis, and hyporeflexia with no sensory abnormalities."WNV is now the most common cause of epidemic viral encephalitis in the United States, and it will likely remain an important cause of neurological disease for the foreseeable future.("Carson PJ, et al. 2006)
- West Nile meningitis (WNM) usually involves fever, headache, and stiff neck. Pleocytosis, an increase of white blood cells in cerebrospinal fluid, is also present. Changes in consciousness are not usually seen and are mild when present.
- West Nile meningoencephalitis is inflammation of both the brain (encephalitis) and meninges (meningitis).
- West Nile poliomyelitis (WNP), an acute flaccid paralysis syndrome associated with WNV infection, is less common than WNM or WNE. This syndrome is generally characterized by the acute onset of asymmetric limb weakness or paralysis in the absence of sensory loss. Pain sometimes precedes the paralysis. The paralysis can occur in the absence of fever, headache, or other common symptoms associated with WNV infection. Involvement of respiratory muscles, leading to acute respiratory failure, can sometimes occur.
- Nonneurologic complications of WNV infection that may rarely occur include fulminant hepatitis, pancreatitis, myocarditis, rhabdomyolysis, orchitis, nephritis, optic neuritis and cardiac dysrhythmias and hemorrhagic fever with coagulopathy. Chorioretinitis may also be more common than previously thought.
- Cutaneous manifestations specifically rashes, are not uncommon in WNV-infected patients; however, there is a paucity of detailed descriptions in case reports and there are few clinical images widely available. Punctate erythematous (?), macular, and papular eruptions, most pronounced on the extremities have been observed in WNV cases and in some cases histopathologic findings have shown a sparse superficial perivascular lymphocytic infiltrate, a manifestation commonly seen in viral exanthems (?). A literature review provides support that this punctate rash is a common cutaneous presentation of WNV infection. (Anderson RC et al.)
|West Nile Virus|
|Group:||Group IV ((+)ssRNA)|
|Species:||West Nile virus|
WNV is one of the Japanese encephalitis antigenic serocomplex of viruses. Image reconstructions and cryoelectron microscopy reveal a 45–50 nm virion covered with a relatively smooth protein surface. This structure is similar to the dengue fever virus; both belong to the genus Flavivirus within the family Flaviviridae. The genetic material of WNV is a positive-sense, single strand of RNA, which is between 11,000 and 12,000 nucleotides long; these genes encode seven nonstructural proteins and three structural proteins. The RNA strand is held within a nucleocapsid formed from 12-kDa protein blocks; the capsid is contained within a host-derived membrane altered by two viral glycoproteins.
Studies of phylogenetic lineages determined 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 zoonosis. 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 in 2010 in a mare and her aborted fetus; 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 broadened the known host range of West Nile virus to include cetaceans.
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, Macaca sylvanus, was the first nonhuman primate 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—can be an early indicator of the arrival of the virus.
The West Nile virus (WNV) is transmitted through female mosquitoes, which are the prime vectors of the virus. Only females feed on blood, and different species have evolved to take a blood meal on preferred types of vertebrate hosts. The infected mosquito species vary according to geographical area; in the US, Culex pipiens (Eastern US), Culex tarsalis (Midwest and West), and Culex quinquefasciatus (Southeast) are the main sources.
The various species that transmit the WNV prefer birds of the Passeriformes order, the largest order of birds. Within that order there is further selectivity with various mosquito species exhibiting preference for different species. In the United States WNV mosquito vectors have shown definitive preference for members of the Corvidae and Thrush family of birds. Amongst the preferred species within these families are the American Crow, a corvid, and the American Robin (Turdus migratorius), a thrush.
The birds develop sufficient viral levels after being infected, to transmit the infection to other biting mosquitoes that in turn go on to infect other birds. In crows and robins, the infection is fatal in 4–5 days. This epizootic viral amplification cycle has been shown to peak 15–16 days before humans become ill. This may be due to the high mortality, and thus depletion of the preferred hosts, i.e., the specific bird species. The mosquitoes become less selective and begin feeding more readily on other animal types such as humans and horses which are considered incidental hosts.
In mammals, the virus does not multiply as readily (i.e., does not develop high viremia during infection), and mosquitoes biting infected mammals are not believed to ingest sufficient virus to become infected, making mammals so-called dead-end hosts.
Direct human-to-human transmission initially was believed to be caused only by occupational exposure, or conjunctive exposure to infected blood. The US outbreak identified additional transmission methods through blood transfusion, organ transplant, intrauterine exposure, and breast feeding. Since 2003, blood banks in the US routinely screen for the virus among their donors. As a precautionary measure, the UK's National Blood Service initially ran a test for this disease in donors who donate within 28 days of a visit to the United States, Canada or the northeastern provinces of Italy and the Scottish National Blood Transfusion Service asks prospective donors to wait 28 days after returning from North America or the northeastern provinces of Italy before donating.
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 pharmacological cocktail of secreted molecules, principally proteins, that can affect vascular constriction, blood coagulation, platelet aggregation, inflammation, and immunity. It clearly alters the immune response in a manner that may be advantageous to a virus. Studies have shown it can specifically modulate the immune response during early virus infection, and mosquito feeding can exacerbate WNV infection, leading to higher viremia and more severe forms of disease.
Vertical transmission, the transmission of a viral or bacterial disease from the female of the species to her offspring, has been observed in various West Nile virus studies, amongst different species of mosquitoes in both the laboratory and in nature. Mosquito progeny infected vertically in autumn, may potentially serve as a mechanism for WNV to overwinter and initiate enzootic horizontal transmission the following spring.
Risk factors independently associated with developing a clinical infection with WNV include a suppressed immune system and a patient history of organ transplantation. For neuroinvasive disease the additional risk factors include older age (>50+), male sex, hypertension, and diabetes mellitus.
A genetic factor also appears to increase susceptibility to West Nile disease. A mutation of the gene CCR5 gives some protection against HIV but leads to more serious complications of WNV infection. Carriers of two mutated copies of CCR5 made up 4.0 to 4.5% of a sample of West Nile disease sufferers, while the incidence of the gene in the general population is only 1.0%.
Preliminary diagnosis is often based on the patient's clinical symptoms, places and dates of travel (if patient is from a non-endemic country or area), activities, and epidemiologic history of the location where infection occurred. A recent history of mosquito bites and an acute febrile illness associated with neurologic signs and symptoms should cause clinical suspicion of WNV.
Diagnosis of West Nile Virus infections is generally accomplished by serologic testing of blood serum or cerebrospinal fluid (CSF), which is obtained via a lumbar puncture. Typical findings of WNV infection include lymphocytic pleocytosis, elevated protein level, reference glucose and lactic acid levels, and no erythrocytes.
Definitive diagnosis of WNV is obtained through detection of virus-specific antibody Immunoglobulin M, (IgM) and neutralizing antibodies. Cases of West Nile virus meningitis and encephalitis that have been serologically confirmed produce similar degrees of CSF pleocytosis and are often associated with substantial CSF neutrophilia. Specimens collected within 8 days following onset of illness may not test positive for West Nile IgM, and testing should be repeated. A positive test for West Nile IgG in the absence of a positive West Nile IgM is indicative of a previous flavavirus infection and is not by itself evidence of an acute West Nile virus infection.
If cases of suspected West Nile virus infection, sera should be collected on both the acute and convalescent phase of the illness. Convalescent specimens should be collected 2–3 weeks after acute specimens.
It is common in serologic testing for cross-reactions to occur among flaviviruses such as Dengue virus (DENV) and tick-borne encephalitis virus, this necessitates caution when evaluating serologic results of flaviviral infections.
Four FDA-cleared WNV IgM ELISA kits are commercially available from different manufacturers in the U.S., each of these kits is indicated for use on serum to aid in the presumptive laboratory diagnosis of WNV infection in patients with clinical symptoms of meningitis or encephalitis. Positive WNV test kits obtained via use of these kits should be confirmed by additional testing at a state health department laboratory or CDC.
In fatal cases, nucleic acid amplification, histopathology with immunohistochemistry and virus culture of autopsy tissues can also be useful. Only a few state laboratories or other specialized laboratories, including those at CDC, are capable of doing this specialized testing
A number of various diseases may present with symptoms similar to those caused by a clinical West Nile virus infection. Those causing neuroinvasive disease symptoms include the enterovirus infection and bacterial meningitis. Accounting for differential diagnoses is a crucial step in the definitive diagnosis of WNV infection. Consideration of a differential diagnosis is required when a patient presents with unexplained febrile illness, extreme headache, encephalitis or meningitis. Diagnostic and serologic laboratory testing utilizing PCR testing and viral culture of CSF to identify the specific pathogen causing the symptoms, is the only currently available means of differentiating between causes of encephalitis and meningitis.
Personal protective measures can be taken to greatly reduce the risk of being bitten by an infected mosquito:
- Using insect repellent on exposed skin to repel mosquitoes. EPA-registered repellents include products containing DEET (N,N-diethylmetatoluamide) and picaridin (KBR 3023). DEET concentrations of 30% to 50% are effective for several hours. Picaridin, available at 7% and 15% concentrations, needs more frequent application. DEET formulations as high as 50% are recommended for both adults and children over 2 months of age. Protect infants less than 2 months of age by using a carrier draped with mosquito netting with an elastic edge for a tight fit.
- When using sunscreen, apply sunscreen first and then repellent. Repellent should be washed off at the end of the day before going to bed.
- Wear long-sleeve shirts, which should be tucked in, long pants, and hats to cover exposed skin.
- The application of permethrin-containing (e.g., Permanone) or other insect repellents to clothing, shoes, tents, mosquito nets, and other gear for greater protection. Permethrin is not labeled for use directly on skin. Most repellent is generally removed from clothing and gear by a single washing, but permethrin-treated clothing is effective for up to 5 washings.
- Be aware that most mosquitoes that transmit disease are most active during twilight periods (dawn and dusk or in the evening). A notable exception is the Asian Tiger mosquito, which is a daytime feeder and is more apt to be found in, or on the periphery of, shaded areas with heavy vegetation. They are now widespread in the United States and in states such as Florida they have been found in all 67 counties.
- Staying in air-conditioned or well-screened housing, and/or sleeping under an insecticide treated bed net. Bed nets should be tucked under mattresses and can be sprayed with a repellent if not already treated with an insecticide.
Monitoring and control
West Nile virus can be sampled from the environment by the pooling of trapped mosquitoes via ovitraps, carbon dioxide-baited light traps, and gravid traps, testing blood samples drawn from wild birds, 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 birds and sentinel chickens, samples must be tested for the presence of WNV antibodies by use of immunohistochemistry (IHC) or Enzyme-Linked Immunosorbent Assay (ELISA).
West Nile control is achieved through mosquito control, by elimination of mosquito breeding sites such as abandoned pools, applying larvacide to active breeding areas and targeting the adult population via lethal ovitraps, aerial spraying of pesticides.
Environmentalists have condemned attempts to control the transmitting mosquitoes by spraying pesticide, saying the detrimental health effects of spraying outweigh the relatively few lives that may be saved, and more environmentally friendly ways of controlling mosquitoes are available. 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 US, Culex pipiens, is a canopy feeder.
Eggs of permanent water mosquitoes can hatch, and the larvae survive, in only a few ounces of water. Less than half the amount that may collect in a discarded coffee cup. Floodwater species lay their eggs on wet soil or other moist surfaces. Hatch time is variable for both types; under favorable circumstances, i.e. warm weather; the eggs of some species may hatch in as little as 1–3 days after being laid.
Used tires often hold stagnant water and are a breeding ground for many species of mosquitoes. Some species such as the Asian Tiger mosquito prefer manmade containers; such as tires, to lay their eggs in. The rapid spread of this aggressive daytime feeding species beyond their native range has been attributed to the used tire trade.
No specific treatment is available for WNV infection. In severe cases treatment consists of supportive care that often involves hospitalization, intravenous fluids, respiratory support, and prevention of secondary infections.
While the general prognosis is favorable, current studies indicate that West Nile Fever can often be more severe than previously recognized, with studies of various recent outbreaks indicating that it may take as long as 60–90 days to recover. Patients with milder WNF are just as likely as those with more severe manifestations of neuroinvasive disease to experience multiple long term (>1+ years) somatic complaints such as tremor, and dysfunction in motor skills and executive functions. Patients with milder illness are just as likely as patients with more severe illness to experience adverse outcomes. Recovery is marked by a long convalescence with fatigue. One study found that neuroinvasive WNV infection was associated with an increased risk for subsequent kidney disease.
WNV was first isolated from a feverish 37-year-old woman at Omogo in the West Nile District of Uganda 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 (1942) and India (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 and Israel. The virus became recognized as a cause of severe human meningoencephalitis in elderly patients during an outbreak in Israel in 1957. The disease was first noted in horses in Egypt and 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 may be an important milestone in the evolving history of this virus. The American outbreak began in College Point, Queens in New York City and was later spread to the neighboring states of New Jersey and Connecticut. The virus is believed to have entered in an infected bird or mosquito, although there is no clear evidence. West Nile virus is now endemic in Africa, Europe, the Middle East, west and central Asia, Oceania (subtype Kunjin), and most recently, North America and is spreading into Central and South America.
Recent outbreaks of West Nile virus encephalitis in humans have occurred in Algeria (1994), Romania (1996 to 1997), the Czech Republic (1997), Congo (1998), Russia (1999), the United States (1999 to 2009), Canada (1999–2007), Israel (2000) and Greece (2010).
A vaccine for horses (ATCvet code: QI05) based on killed viruses exists; some zoos have given this vaccine to their birds, although its effectiveness 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 they are, in turn, capable of infecting native mosquitoes and thus continuing the disease cycle. AMD3100, which had been proposed as an antiretroviral drug for HIV, has shown promise against West Nile encephalitis. Morpholino antisense oligos conjugated to cell penetrating peptides have been shown to partially protect mice from WNV disease. There have also been attempts to treat infections using ribavirin, intravenous immunoglobulin, or alpha interferon. GenoMed, a U.S. biotech company, has found that blocking angiotensin II can treat the "cytokine storm" of West Nile virus encephalitis as well as other viruses.
- Nash D, Mostashari F, Fine A, et al. (June 2001). "The outbreak of West Nile virus infection in the New York City area in 1999". N. Engl. J. Med. 344 (24): 1807–14. doi:10.1056/NEJM200106143442401. PMID 11407341.
- Fox, M. (May 13, 2013). "2012 was deadliest year for West Nile in US, CDC says". NBC News. Retrieved May 13, 2013.
- Steinman, A.; Banet-Noach, C.; Tal, S.; Levi, O.; Simanov, L.; Perk, S.; Malkinson, M.; Shpigel, N. (2003). "West Nile Virus Infection in Crocodiles". Emerging Infectious Diseases 9 (7): 887–889. doi:10.3201/eid0907.020816. PMC 3023443. PMID 12899140.
- Klenk, K.; Snow, J.; Morgan, K.; Bowen, R.; Stephens, M.; Foster, F.; Gordy, P.; Beckett, S.; Komar, N.; Gubler, D.; Bunning, M. (2004). "Alligators as West Nile Virus Amplifiers". Emerging Infectious Diseases 10 (12): 2150–2155. doi:10.3201/eid1012.040264. PMC 3323409. PMID 15663852.
- "West Nile Virus: What You Need to Know CDC Fact Sheet". www.CDC.gov. Retrieved 2012-04-09.
- Olejnik E (1952). "Infectious adenitis transmitted by Culex molestus". Bull Res Counc Isr 2: 210–1.
- Davis LE, DeBiasi R, Goade DE et al. (Sep 2006). "West Nile virus neuroinvasive disease". Ann Neurol 60 (3): 286–300. doi:10.1002/ana.20959. PMID 16983682.
- Flores Anticona EM, Zainah H, Ouellette DR, Johnson LE (2012). "Two case reports of neuroinvasive west nile virus infection in the critical care unit". Case Rep Infect Dis 2012: 839458. doi:10.1155/2012/839458. PMC 3433121. PMID 22966470.
- Carson PJ, Konewko P, Wold KS, et al. (2006). "Long-term clinical and neuropsychological outcomes of West Nile virus infection". Clin. Infect. Dis. 43 (6): 723–30. doi:10.1086/506939. PMID 16912946.
- Asnis DS, Conetta R, Teixeira AA, Waldman G, Sampson BA (March 2000). "The West Nile Virus outbreak of 1999 in New York: the Flushing Hospital experience". Clin. Infect. Dis. 30 (3): 413–8. doi:10.1086/313737. PMID 10722421.
- Montgomery SP, Chow CC, Smith SW, Marfin AA, O'Leary DR, Campbell GL (2005). "Rhabdomyolysis in patients with west nile encephalitis and meningitis". Vector-Borne and Zoonotic Diseases 5 (3): 252–7. doi:10.1089/vbz.2005.5.252. PMID 16187894.
- Smith RD, Konoplev S, DeCourten-Myers G, Brown T (February 2004). "West Nile virus encephalitis with myositis and orchitis". Hum. Pathol. 35 (2): 254–8. doi:10.1016/j.humpath.2003.09.007. PMID 14991545.
- Anninger WV, Lomeo MD, Dingle J, Epstein AD, Lubow M (2003). "West Nile virus-associated optic neuritis and chorioretinitis". Am. J. Ophthalmol. 136 (6): 1183–5. doi:10.1016/S0002-9394(03)00738-4. PMID 14644244.
- Paddock CD, Nicholson WL, Bhatnagar J, et al. (June 2006). "Fatal hemorrhagic fever caused by West Nile virus in the United States". Clin. Infect. Dis. 42 (11): 1527–35. doi:10.1086/503841. PMID 16652309.
- Shaikh S, Trese MT (2004). "West Nile virus chorioretinitis". Br J Ophthalmol 88 (12): 1599–60. doi:10.1136/bjo.2004.049460. PMC 1772450. PMID 15548822.
- Anderson RC, Horn KB, Hoang MP, Gottlieb E, Bennin B (November 2004). "Punctate exanthem of West Nile Virus infection: report of 3 cases". J. Am. Acad. Dermatol. 51 (5): 820–3. doi:10.1016/j.jaad.2004.05.031. PMID 15523368.
- Lanciotti RS, Ebel GD, Deubel V, et al. (June 2002). "Complete genome sequences and phylogenetic analysis of West Nile virus strains isolated from the United States, Europe, and the Middle East". Virology 298 (1): 96–105. doi:10.1006/viro.2002.1449. PMID 12093177.
- Galli M, Bernini F, Zehender G (July 2004). "Alexander the Great and West Nile virus encephalitis". Emerging Infect. Dis. 10 (7): 1330–2; author reply 1332–3. doi:10.3201/eid1007.040396. PMID 15338540.
- West, Christy (2010-02-08). Different West Nile Virus Genetic Lineage Evolving?. The Horse, online edition. Retrieved 2010-02-10.
- Venter M, Human S, van Niekerk S, Williams J, van Eeden C, Freeman F (August 2011). "Fatal neurologic disease and abortion in mare infected with lineage 1 West Nile virus, South Africa". Emerging Infect. Dis. 17 (8): 1534–6. doi:10.3201/eid1708.101794. PMC 3381566. PMID 21801644.
- St Leger J, Wu G, Anderson M, Dalton L, Nilson E, Wang D (2011). "West Nile virus infection in killer whale, Texas, USA, 2007". Emerging Infect. Dis. 17 (8): 1531–3. doi:10.3201/eid1708.101979. PMC 3381582. PMID 21801643.
- Hogan, C. Michael (2008). Barbary Macaque: Macaca sylvanus, GlobalTwitcher.com
- Hayes EB, Komar N, Nasci RS, Montgomery SP, O'Leary DR, Campbell GL (2005). "Epidemiology and transmission dynamics of West Nile virus disease". Emerging Infect. Dis. 11 (8): 1167–73. doi:10.3201/eid1108.050289a. PMC 3320478. PMID 16102302.
- "First Evidence of West Nile Virus Amplification and relationship to Human Infection" (PDF).
- Taylor RM, Hurlbut HS, Dressler HR, Spangler EW, Thrasher D (1953). "Isolation of West Nile virus from Culex mosquitoes". J Egypt Med Assoc 36 (3): 199–208. PMID 13084817.
- Centers for Disease Control and Prevention (CDC) (2002). "Laboratory-acquired West Nile virus infections—United States, 2002". MMWR Morb. Mortal. Wkly. Rep. 51 (50): 1133–5. PMID 12537288.
- Fonseca K, Prince GD, Bratvold J, et al. (2005). "West Nile virus infection and conjunctive exposure". Emerging Infect. Dis. 11 (10): 1648–9. doi:10.3201/eid1110.040212. PMC 3366727. PMID 16355512.
- Centers for Disease Control and Prevention (CDC) (2002). "Investigation of blood transfusion recipients with West Nile virus infections". MMWR Morb. Mortal. Wkly. Rep. 51 (36): 823. PMID 12269472.
- Centers for Disease Control and Prevention (CDC) (2002). "West Nile virus infection in organ donor and transplant recipients—Georgia and Florida, 2002". MMWR Morb. Mortal. Wkly. Rep. 51 (35): 790. PMID 12227442.
- Centers for Disease Control and Prevention (CDC) (2002). "Intrauterine West Nile virus infection—New York, 2002". MMWR Morb. Mortal. Wkly. Rep. 51 (50): 1135–6. PMID 12537289.
- Centers for Disease Control and Prevention (CDC) (2002). "Possible West Nile virus transmission to an infant through breast-feeding—Michigan, 2002". MMWR Morb. Mortal. Wkly. Rep. 51 (39): 877–8. PMID 12375687.
- Centers for Disease Control and Prevention (CDC) (2003). "Detection of West Nile virus in blood donations—United States, 2003". MMWR Morb. Mortal. Wkly. Rep. 52 (32): 769–72. PMID 12917583.
- West Nile Virus. Scottish National Blood Transfusion Service.
- Schneider BS, McGee CE, Jordan JM, Stevenson HL, Soong L, Higgs S (2007). "Prior exposure to uninfected mosquitoes enhances mortality in naturally-transmitted West Nile virus infection". In Baylis, Matthew. PLoS ONE 2 (11): e1171. doi:10.1371/journal.pone.0001171. PMC 2048662. PMID 18000543.
- Styer LM, Bernard KA, Kramer LD (2006). "Enhanced early West Nile virus infection in young chickens infected by mosquito bite: effect of viral dose". Am. J. Trop. Med. Hyg. 75 (2): 337–45. PMID 16896145.
- Schneider BS, Soong L, Girard YA, Campbell G, Mason P, Higgs S (2006). "Potentiation of West Nile encephalitis by mosquito feeding". Viral Immunol. 19 (1): 74–82. doi:10.1089/vim.2006.19.74. PMID 16553552.
- Wasserman HA, Singh S, Champagne DE (2004). "Saliva of the Yellow Fever mosquito, Aedes aegypti, modulates murine lymphocyte function". Parasite Immunol. 26 (6–7): 295–306. doi:10.1111/j.0141-9838.2004.00712.x. PMID 15541033.
- Limesand KH, Higgs S, Pearson LD, Beaty BJ (2003). "Effect of mosquito salivary gland treatment on vesicular stomatitis New Jersey virus replication and interferon alpha/beta expression in vitro". J. Med. Entomol. 40 (2): 199–205. doi:10.1603/0022-2585-40.2.199. PMID 12693849.
- Wanasen N, Nussenzveig RH, Champagne DE, Soong L, Higgs S (2004). "Differential modulation of murine host immune response by salivary gland extracts from the mosquitoes Aedes aegypti and Culex quinquefasciatus". Med. Vet. Entomol. 18 (2): 191–9. doi:10.1111/j.1365-2915.2004.00498.x. PMID 15189245.
- Zeidner NS, Higgs S, Happ CM, Beaty BJ, Miller BR (1999). "Mosquito feeding modulates Th1 and Th2 cytokines in flavivirus susceptible mice: an effect mimicked by injection of sialokinins, but not demonstrated in flavivirus resistant mice". Parasite Immunol. 21 (1): 35–44. doi:10.1046/j.1365-3024.1999.00199.x. PMID 10081770.
- Schneider BS, Soong L, Zeidner NS, Higgs S (2004). "Aedes aegypti salivary gland extracts modulate anti-viral and TH1/TH2 cytokine responses to sindbis virus infection". Viral Immunol. 17 (4): 565–73. doi:10.1089/vim.2004.17.565. PMID 15671753.
- Bugbee, LM; Forte LR (September 2004). "The discovery of West Nile virus in overwintering Culex pipiens (Diptera: Culicidae) mosquitoes in Lehigh County, Pennsylvania". Journal of the American Mosquito Control Association 20 (3): 326–7. PMID 15532939.
- Goddard LB, Roth AE, Reisen WK, Scott TW (November 2003). "Vertical transmission of West Nile Virus by three California Culex (Diptera: Culicidae) species". J. Med. Entomol. 40 (6): 743–6. doi:10.1603/0022-2585-40.6.743. PMID 14765647.
- Kumar D, Drebot MA, Wong SJ, et al. (2004). "A seroprevalence study of West Nile virus infection in solid organ transplant recipients". Am. J. Transplant. 4 (11): 1883–8. doi:10.1111/j.1600-6143.2004.00592.x. PMID 15476490.
- Jean CM, Honarmand S, Louie JK, Glaser CA (December 2007). "Risk factors for West Nile virus neuroinvasive disease, California, 2005". Emerging Infect. Dis. 13 (12): 1918–20. doi:10.3201/eid1312.061265. PMC 2876738. PMID 18258047.
- Kumar D, Drebot MA, Wong SJ, et al. (2004). "A seroprevalence study of west nile virus infection in solid organ transplant recipients". Am. J. Transplant. 4 (11): 1883–8. doi:10.1111/j.1600-6143.2004.00592.x. PMID 15476490.
- Glass, WG; Lim JK, Cholera R, Pletnev AG, Gao JL, Murphy PM (October 17, 2005). "Chemokine receptor CCR5 promotes leukocyte trafficking to the brain and survival in West Nile virus infection". Journal of Experimental Medicine 202 (8): 1087–98. doi:10.1084/jem.20042530. PMC 2213214. PMID 16230476.
- Glass, WG; McDermott DH, Lim JK, Lekhong S, Yu SF, Frank WA, Pape J, Cheshier RC, Murphy PM (January 23, 2006). "CCR5 deficiency increases risk of symptomatic West Nile virus infection". Journal of Experimental Medicine 203 (1): 35–40. doi:10.1084/jem.20051970. PMC 2118086. PMID 16418398.
- Tyler KL, Pape J, Goody RJ, Corkill M, Kleinschmidt-DeMasters BK (February 2006). "CSF findings in 250 patients with serologically confirmed West Nile virus meningitis and encephalitis". Neurology 66 (3): 361–5. doi:10.1212/01.wnl.0000195890.70898.1f. PMID 16382032.
- "2012 DOHMH Advisory #8: West Nile Virus" (PDF). NYC.
- Papa A, Karabaxoglou D, Kansouzidou A (October 2011). "Acute West Nile virus neuroinvasive infections: cross-reactivity with dengue virus and tick-borne encephalitis virus". J. Med. Virol. 83 (10): 1861–5. doi:10.1002/jmv.22180. PMID 21837806.
- Rios L, Maruniak JE (October 2011). "Asian Tiger Mosquito, Aedes albopictus (Skuse) (Insecta: Diptera: Culicidae)". Department of Entomology and Nematology, University of Florida. EENY-319.
- Jozan, M; Evans R, McLean R, Hall R, Tangredi B, Reed L, Scott J (Fall 2003). "Detection of West Nile virus infection in birds in the United States by blocking ELISA and immunohistochemistry". Vector-Borne and Zoonotic Diseases 3 (3): 99–110. doi:10.1089/153036603768395799. PMID 14511579.
- Hall, RA; Broom AK, Hartnett AC, Howard MJ, Mackenzie JS (February 1995). "Immunodominant epitopes on the NS1 protein of MVE and KUN viruses serve as targets for a blocking ELISA to detect virus-specific antibodies in sentinel animal serum". Journal of Virological Methods 51 (2–3): 201–10. doi:10.1016/0166-0934(94)00105-P. PMID 7738140.
- "Mosquito Monitoring and Management". National Park Service.
- Oklahoma State University: Mosquitoes and West Nile virus
- Benedict MQ, Levine RS, Hawley WA, Lounibos LP (2007). "Spread of the tiger: global risk of invasion by the mosquito Aedes albopictus". Vector-Borne and Zoonotic Diseases 7 (1): 76–85. doi:10.1089/vbz.2006.0562. PMC 2212601. PMID 17417960.
- Watson JT, Pertel PE, Jones RC, et al. (September 2004). "Clinical characteristics and functional outcomes of West Nile Fever". Ann. Intern. Med. 141 (5): 360–5. doi:10.7326/0003-4819-141-5-200409070-00010. PMID 15353427.
- Klee AL, Maidin B, Edwin B et al. (Aug 2004). "Long-term prognosis for clinical West Nile virus infection". Emerg Infect Dis 10 (8): 1405–11. doi:10.3201/eid1008.030879. PMC 3320418. PMID 15496241.
- Nolan MS, Podoll AS, Hause AM, Akers KM, Finkel KW, Murray KO (2012). "Prevalence of chronic kidney disease and progression of disease over time among patients enrolled in the Houston West Nile virus cohort". In Wang, Tian. PLoS ONE 7 (7): e40374. doi:10.1371/journal.pone.0040374. PMC 3391259. PMID 22792293.
- "New Study Reveals: West Nile virus is far more menacing & harms far more people". The Guardian Express. The Guardian Express. 26 August 2012. Retrieved 26 August 2012.
- Smithburn KC, Hughes TP, Burke AW, Paul JH (June 1940). "A Neurotropic Virus Isolated from the Blood of a Native of Uganda". Am. J. Trop. Med. 20 (1): 471–92.
- Work TH, Hurlbut HS, Taylor RM (1953). "Isolation of West Nile virus from hooded crow and rock pigeon in the Nile delta". Proc. Soc. Exp. Biol. Med. 84 (3): 719–22. doi:10.3181/00379727-84-20764. PMID 13134268.
- Bernkopf H, Levine S, Nerson R (1953). "Isolation of West Nile virus in Israel". J. Infect. Dis. 93 (3): 207–18. doi:10.1093/infdis/93.3.207. PMID 13109233.
- Calisher CH (2000). "West Nile virus in the New World: appearance, persistence, and adaptation to a new econiche—an opportunity taken". Viral Immunol. 13 (4): 411–4. doi:10.1089/vim.2000.13.411. PMID 11192287.
- "Vertebrate Ecology". West Nile Virus. Division of Vector-Borne Diseases, CDC. 30 April 2009.
- Deas, Tia S; Bennett CJ, Jones SA, Tilgner M, Ren P, Behr MJ, Stein DA, Iversen PL, Kramer LD, Bernard KA, Shi PY (May 2007). "In vitro resistance selection and in vivo efficacy of morpholino oligomers against West Nile virus". Antimicrob Agents Chemother 51 (7): 2470–82. doi:10.1128/AAC.00069-07. PMC 1913242. PMID 17485503.
- Hayes EB, Sejvar JJ, Zaki SR, Lanciotti RS, Bode AV, Campbell GL (2005). "Virology, pathology, and clinical manifestations of West Nile virus disease". Emerging Infect. Dis. 11 (8): 1174–9. doi:10.3201/eid1108.050289b. PMC 3320472. PMID 16102303.
- Moskowitz DW, Johnson FE (2004). "The central role of angiotensin I-converting enzyme in vertebrate pathophysiology". Curr Top Med Chem 4 (13): 1433–54. doi:10.2174/1568026043387818. PMID 15379656.
- Arroyo, J.; Miller, C.; Catalan, J.; Myers, G. A.; Ratterree, M. S.; Trent, D. W.; Monath, T. P. (2004). "ChimeriVax-West Nile Virus Live-Attenuated Vaccine: Preclinical Evaluation of Safety, Immunogenicity, and Efficacy". Journal of Virology 78 (22): 12497–12507. doi:10.1128/JVI.78.22.12497-12507.2004. PMC 525070. PMID 15507637.
- Biedenbender, R.; Bevilacqua, J.; Gregg, A. M.; Watson, M.; Dayan, G. (2011). "Phase II, Randomized, Double-Blind, Placebo-Controlled, Multicenter Study to Investigate the Immunogenicity and Safety of a West Nile Virus Vaccine in Healthy Adults". Journal of Infectious Diseases 203 (1): 75–84. doi:10.1093/infdis/jiq003. PMC 3086439. PMID 21148499.
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- De Filette M, Ulbert S, Diamond M, Sanders NN (2012). "Recent progress in West Nile virus diagnosis and vaccination". Vet. Res. 43 (1): 16. doi:10.1186/1297-9716-43-16. PMC 3311072. PMID 22380523.
- "West Nile Virus". Division of Vector-Borne Diseases, U.S. Centers for Disease Control and Prevention (CDC).
- CDC—West Nile Virus—NIOSH Workplace Safety and Health Topic
- Recommendations for Protecting Laboratory, Field, and Clinical Workers from West Nile Virus Exposure
- West Nile Virus Resource Guide—National Pesticide Information Center
- Vaccine Research Center (VRC)—Information concerning WNV vaccine research studies
- Nature news article on West Nile paralysis
- CBC News Coverage of West Nile in Canada
- Gene mutation turned West Nile virus into killer disease among crows
- Virus Pathogen Database and Analysis Resource (ViPR): Flaviviridae
- Species Profile- West Nile Virus (Flavivirus), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for West Nile Virus.
- 3D macromolecular structures of the West Nile Virus archived in the EM Data Bank(EMDB)
- West Nile Virus—West Nile Encephalitis Brain Scans