Context

A six year old child died in Malappuram, Kerala due to West Nile Fever, claimed to be the first victim of the virus in the recent past.

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• Health experts claimed this could be the first confirmed death in the State due to the relatively unknown viral infection that leads to neurological diseases.
• Birds are the natural hosts of the virus and vaccine is not available for it.

What is West Nile Fever?

• West Nile fever is a zoonotic disease (an animal disease affecting humans). Disease is caused by West Nile virus (WNV), which is a flavivirus related to the viruses that cause St. Louis encephalitis, Japanese encephalitis, and yellow fever.
• WNV is commonly found in Africa, Europe, the Middle East, North America and West Asia.
• WNV is maintained in nature in a cycle involving transmission between birds and mosquitoes.
• Humans, horses and other mammals can be infected.

Had there been any major outbreak in the past?

• The largest outbreaks occurred in Greece, Israel, Romania, Russia and USA. Outbreak sites are on major birds’ migratory routes.
• In its original range, WNV was prevalent throughout Africa, parts of Europe, Middle East, West Asia, and Australia.
• Since its introduction in 1999 into USA, the virus has spread and is now widely established from Canada to Venezuela.

What is the mode of transmission?

• Human infection is most often the result of bites from infected mosquitoes. 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. During later blood meals (when mosquitoes bite), the virus may be injected into humans and animals, where it can multiply and possibly cause illness.
• The virus may also be transmitted through contact with other infected animals, their blood, or other tissues.

What are the signs and symptoms of the WNV?

• 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.
• It is estimated that approximately 1 in 150 persons infected with the West Nile virus will develop a more severe form of disease.
• Serious illness can occur in people of any age, however people over the age of 50 and some immune-compromised persons (for example, transplant patients) are at the highest risk for getting severely ill when infected with WNV.
• The incubation period is usually 3 to 14 days.
  
  

  West Nile Fever in India: It is highly prevalent in India. Infection usually presents as a mild, non-fatal dengue like illness in humans. Febrile illness and encephalitis cases in epidemic form were observed in Udaipur district of Rajasthan, Buldhana, Marathwada and Khandesh districts of Maharashtra. Human sera collected from Tamil Nadu, Karnataka, Andhra Pradesh, Maharashtra, Gujarat, Madhya Pradesh, Orissa and Rajasthan showed presence of WNV neutralizing antibodies. Serologically confirmed cases of WNV infections were reported from Vellore and Kolar districts during 1977, 1978 and 1981. Presence of WNV was documented in north- eastern region of India during the year 2006 from four districts (Japanese encephalitis (JE) endemic areas) of Assam. During an outbreak of AES in Kerala, in May 2011, presence of WNV was confirmed in clinical specimens. Since then, WNV encephalitis cases have regularly been reported in Kerala.