West Nile virus infection
West Nile virus (WNV) is a type strain of flaviviruses and is related to Japanese encephalitis group. The virus was first isolated from a woman in the West Nile District of Uganda in 1937. The most serious manifestation of WNV infection is fatal encephalitis in humans and horses, as well as mortality in certain domestic and wild birds. The ecology was characterized in Egypt in the 1950s. The virus became recognized as a cause of severe inflammation of the spinal cord and brain in humans during an outbreak in Israel in 1957. Equine disease was first recorded in Egypt and France in the early 1960s. Recent outbreaks of WNV encephalitis in humans have occurred in Algeria (1994), Romania (1996-1997), Czech Republic (1997), Congo (1998), Russia (1999), USA (1999-2001) and Israel (2000). Epizootics of disease in horses occurred in Morocco (1996), Italy (1998), USA (1999-2001) and France (2000). WNV is highly prevalent in India, it is known to be active in mosquitoes, birds and pigs and usually causes a mild, non-fatal dengue like illness in humans. However, febrile illness in epidemic form and clinically overt encephalitis cases were observed in Udaipur area of Rajasthan, as well as Marathwada and Khandesh areas of Maharashtra.
Transmission to humans is through mosquito bite. A mosquito becomes infected by biting a bird that carries the virus. The Culex mosquito and many other insects found positive include species that feed on both avian and mammalian hosts. Recent studies in the lab indicate that WNV can be transmitted from bird-to-bird. This transmission from bird-to-bird, without the intervention of mosquitoes raises new questions about methods of transmission of the disease. In south India, JEV/WNV neutralizing antibodies were detected in birds mainly from the pond herons (Ardeola grayii) and cattle egrets (Bubulcus ibis). This indicates the possible involvement of ardeid birds in the natural cycle of WNV in India.
Symptoms and lesions: WNV is primarily an avian disease and as many as 10,000 crows died from the spreading infections in metropolitan New York in 2000. The deaths of numerous horses in the area also were attributed to the virus, which caused encephalitis. It is generally a milder infection with a fatality rate of 3% to 15% of all human cases and symptoms of fever, headache, body aches, skin rashes and swollen lymph glands. More severe infections may be a neck stiffness, disorientation, coma, tremors, convulsions, muscle weakness and paralysis.
Diagnosis: WNV infection is diagnosed by serological methods. In a human serum samples, MAC ELISA (IgM-antibody capture ELISA) is routinely used to detect acute infection. A commercially available arboviral immunofluorescence assay has been used for the screening of WNV infection in human. Recently, the RT-PCR and Real Time PCR methods for the detection of virus specific genome have been extensively used by several workers.
Prevention and control: In India, since no studies have been carried out for the control of WNV, the strategies recommended for the control of Culex mosquitoes, the known vectors of JEV could be applicable. The integrated vector control strategies includes the use of personal protection measures like protective clothing, bed nets, both chemical and neem-based repellants, insecticides, insecticide impregnated curtains, and biological control methods by larvivorous fish, introducing natural parasites, predators and bacterial agents.