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The Kerala government issued an alert in the State against West Nile fever, a mosquito-borne viral infection, after one death and eight cases were reported from Kozhikode, Malappuram and Thrissur districts in recent days
The infection was confirmed after samples of blood and cerebrospinal fluid of suspected patients were examined at the Virus Research and Diagnostic Lab attached to the Kozhikode medical college hospital.
They were later sent to the National Institute of Virology, Pune, for official confirmation.
West Nile Virus
The West Nile Virus (WNV) 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, WNV 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
WNV 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.
Transmission Cycle:
Principal vector for transmission is the culex species of mosquitoes.
Birds act as the reservoir host of the virus.
Infected mosquitoes transmit WNV between and among humans and animals, including birds.
When a mosquito feeds on infected birds, they become infected.
The virus circulates in the blood of those infected mosquitoes for a few days, eventually getting into the mosquito’s salivary glands.
The virus may get injected into humans and animals during later blood meals (when mosquito bites).
Therein, WNV can multiply and possibly cause illness.
WNV can also get transmitted from an infected mother to her child through blood transfusion or via exposure to the virus in laboratories.
No instance of transmission by contact with infected humans or animals has been reported.
It does not spread through eating infected animals, including birds.
Generally, the incubation period for WNV disease is 2-6 days.
However, this may range from 2-14 days, and can also be several weeks in people whose immunity is compromised.
According to the World Health Organization (WHO), no human-to-human transmission of WNV through casual contact has been reported till date
Symptoms
Symptoms of the infection include high fever, headache, neck stiffness, disorientation, stupor, coma, tremors, convulsions, muscle weakness, and paralysis.
Most of the symptoms are similar to that of Japanese encephalitis.
However, 80% of the patients need not show any symptoms.
Cure
The WHO says that the treatment is supportive for patients with neuro-invasive West Nile virus, often involving hospitalisation, intravenous fluids, respiratory support, and prevention of secondary infections.
No vaccine is available for humans.
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