West Nile Virus

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.T

Horses, just like humans, are “dead-end” hosts, meaning that while they become infected, they do not spread the infection. Symptomatic infections in horses are also rare and generally mild, but can cause neurologic disease, including fatal encephalomyelitis.

Signs and symptoms:

  • Infection with WNV is either asymptomatic (no symptoms) in around 80% of infected people, or can lead to West Nile fever or severe West Nile disease.
  • About 20% of people who become infected with WNV will develop West Nile fever. Symptoms include fever, headache, tiredness, and body aches, nausea, vomiting, occasionally with a skin rash (on the trunk of the body) and swollen lymph glands.

The symptoms of severe disease (also called neuroinvasive disease, such as West Nile encephalitis or meningitis or West Nile poliomyelitis) include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis

Treatment is supportive for patients with neuro-invasive West Nile virus, often involving hospitalization, intravenous fluids, respiratory support, and prevention of secondary infections. No vaccine is available for humans.

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