West Nile Virus

West Nile Virus


The Kerala government has issued an alert in the state following reports of West Nile fever, a mosquito-borne viral infection, with one death and eight cases reported in Kozhikode, Malappuram, and Thrissur districts.

GS-02 (Health)

Key Highlights:

  • Diagnostic Process: The infection was confirmed through blood and cerebrospinal fluid samples examined at the Virus Research and Diagnostic Lab, later sent to the National Institute of Virology, Pune, for official confirmation.
  • Symptoms: Symptoms of West Nile fever include high fever, headache, neck stiffness, disorientation, and muscle weakness, often resembling Japanese encephalitis. However, 80% of patients may not exhibit any symptoms.
  • Transmission: The disease is spread by Culex mosquitoes, primarily through bites from infected mosquitoes feeding on birds. Human-to-human transmission has not been reported.
  • Treatment: Supportive treatment is provided for patients with neuro-invasive West Nile virus, including hospitalization, intravenous fluids, and respiratory support. Currently, there is no vaccine available for humans against West Nile fever.
  • WNV activity has been reported in various parts of India since 1952. The virus has been isolated from mosquitoes and humans in states like Maharashtra, Andhra Pradesh, Tamil Nadu, and Karnataka. Establishing active animal health surveillance systems and implementing mosquito control measures are crucial preventive strategies.

About West Nile Virus (WNV):

  • West Nile Virus (WNV) is a single-stranded RNA virus belonging to the flavivirus family. It shares characteristics with viruses causing diseases like St. Louis encephalitis, Japanese encephalitis, and yellow fever.
  • The virus primarily spreads through infected mosquitoes, primarily of the Culex species, which can transmit it to humans and animals during blood feeding.
  • Understanding its transmission, symptoms, and preventive measures is crucial in combating its spread.


  • The Culex species of mosquitoes serve as the primary vectors for WNV transmission
  • Infected mosquitoes acquire the virus by feeding on birds, which act as reservoir hosts.
  • The virus circulates in the bird’s bloodstream for several days before reaching the mosquito’s salivary glands.
  • When infected mosquitoes bite humans or animals, the virus can be transmitted, potentially causing illness.
  • While transmission through blood transfusion or from mother to child is possible, human-to-human transmission is rare.

Incubation Period:

  • According to the US Center for Disease Control and Prevention (CDC), the incubation period for WNV disease typically ranges from 2 to 6 days, although it can vary from 2 to 14 days.
  • In immunocompromised individuals, the incubation period may extend to several weeks. Human-to-human transmission through casual contact has not been documented.

Preventive Measures:

  • Given that WNV outbreaks often coincide with peak mosquito activity, personal protective measures like using mosquito repellents are recommended.
  • Public health departments should focus on larval source reduction to control mosquito breeding.
  • However, no specific prophylaxis, treatment, or vaccine for WNV is available, and supportive care is provided to patients with neuroinvasive disease.
  • Understanding the transmission, symptoms, and preventive measures associated with WNV is essential in managing and mitigating the impact of this mosquito-borne virus