Commonly found in Africa, Europe, the Middle East, North America and West Asia, the West Nile Virus (WNV) is a viral infection which is typically spread by mosquitoes and can cause neurological disease as well as death in people. First detected in a woman in West Nile district of Uganda in 1937, the virus was later identified in birds (crows and columbiformes) in Nile delta region in 1953. According to the World Health Organisation (WHO), the virus is a member of the flavivirus genus and belongs to the Japanese encephalitis antigenic complex of the family Flaviviridae. The largest outbreaks of the virus were recorded in Greece, Israel, Romania, Russia and USA.
How does the virus spread or get transmitted?
The disease is transmitted to humans through mosquito bites. Mosquitoes become infected when they feed on infected birds, which circulate the virus in their blood for a few days. The virus gets transmitted into the mosquito’s salivary glands, from where it is injected into humans as well as animals through mosquito bites. The virus can multiply in the process and possibly cause illness.
WNL may also be transmitted through contact with other infected animals, their blood or other tissues.
Till date, no human-to-human transmission through casual contact has been reported.
A very small proportion of human infections have occurred through organ transplant, blood transfusions and breast milk while one case of transplacental (mother to child) transmission has been reported.
Symptoms of West Nile Virus
The infection is either asymptomatic (no symptoms) or can result in West Nile fever or severe West Nile disease. People infected with WNV suffer from fever, headache, fatigue, body aches, nausea, vomiting, occasionally with a skin rash (on the trunk of the body) and swollen lymph glands.
In case of severe West Nile disease (also called neuroinvasive disease, such as West Nile encephalitis or meningitis or West Nile poliomyelitis), the patient suffers from headache, high fever, neck stiffness, disorientation, stupor, coma, tremors, convulsions, muscle weakness and paralysis. According to WHO, one in 150 persons infected with the virus will develop a severe form of the disease. While this can occur in people of any age, those over the age of 50 and some immunocompromised persons (for example, transplant patients) are at more risk of getting severely affected.
The incubation period is usually 3 to 14 days.
Diagnosis of West Nile Virus
According to WHO, the virus can be detected through a number of medical tests:
-IgG antibody sero-conversion (or significant increase in antibody titers) in two serial specimen collected at a one week interval by enzyme-linked immunosorbent assay (ELISA);
-IgM antibody capture enzyme-linked immunosorbent assay (ELISA); neutralisation assays;
-viral detection by reverse transcription polymerase chain reaction (RT-PCR) assay, and
-virus isolation by cell culture.
-IgM can be detected in nearly all cerebrospinal fluid (CSF) and serum specimens received from WNV infected patients at the time of their clinical presentation. Serum IgM antibody may persist for more than a year.
Treatment of West Nile Virus
Those infected with the virus are required to be hospitalised and put on respiratory support and intravenous fluids. No vaccine is available for humans.
Prevention of infection in health care set-up
Health care workers caring for patients with suspected or confirmed WNV infection, or handling specimens from them, should strictly follow standard infection control precautions. The samples taken from people and animals with suspected WNV infection should be handled by trained staff working in suitably equipped laboratories.