West Nile Virus

West Nile Virus

West Nile Virus


  • The West Nile Virus is a flavivirus related to the viruses that are also responsible for causing St. Louis encephalitis, Japanese encephalitis, and yellow fever.
  • It is a mosquito-borne, single-stranded RNA virus.

Global Prevalence

  • Along all major bird migratory routes, West Nile Virus outbreak sites are found.
  • Africa, Europe, the Middle East, North America, and West Asia are the regions where the virus is commonly found.
  • Usually, WNV infections peak during the period when mosquito vectors are most active and the ambient temperature is high enough for virus multiplication for most of the countries.

Prevalence in India

  • In Mumbai in the year 1952, the antibodies against West Nile Virus were first detected in humans.
  • Since then, the virus activity has been reported in southern, central, and western India.
  • In Andhra Pradesh and Tamil Nadu, WNV was isolated from Culex Vishnui mosquitoes.
  • In Maharashtra, it was isolated from Culex quinquefasciatus mosquitoes.
  • In Karnataka, it has been isolated from humans.
  • Further, WNV-neutralizing antibodies were found to be present in human serum collected from Tamil Nadu, Karnataka, Andhra Pradesh, Maharashtra, Gujarat, Madhya Pradesh, Odisha, Rajasthan and Assam.
  • In 1977, 1978, and 1981, serologically confirmed cases of WNV infections were reported in Vellore and Kolar districts, and in West Bengal in 2017.
  • During an acute encephalitis outbreak in Kerala, the complete genome sequence of WNV was isolated in 2013.
  • The association of West Nile Virus with eye infection in Tamil Nadu had been clearly established during an epidemic of mysterious fever in the first half of 2010.


  • West Nile Virus was first isolated in a woman in the West Nile district of Uganda in 1937.
  • It was identified in birds in the Nile Delta region in 1953. Before 1997, WNV was not considered pathogenic for birds.
  • Human infections attributable to WNV have been reported in many countries for over 50 years.

How does it spread?

  • Culex species of mosquitos act as the principal vectors for transmission.
  • It is transmitted by infected mosquitoes between and among humans and animals, including birds, which are the reservoir host of the virus.
  • Mosquitoes become infected when they feed on infected birds, which circulate the virus in their blood for a few days.
  • The virus eventually gets into the mosquito’s salivary glands.
  • When mosquitoes bite, the virus may be injected into humans and animals, where it can multiply and possibly cause illness.
  • It can also spread through blood transfusion, from an infected mother to her child, or through exposure to the virus in laboratories.
  • It is not known to spread by contact with infected humans or animals.

Related Links:

H5N1 Bird FluWorld Health Organisation (WHO)
CRISPR TechnologyAntimicrobial Resistance (AMR)