The West Nile Virus, or WNV, is responsible for numerous infections and deaths worldwide. It is a flavivirus, similar to those that cause St. Louis encephalitis, Japanese encephalitis, and yellow fever. WNV, which originates from the blood of birds, can be transmitted through mosquitoes to both humans and animals, leading to serious illnesses. This virus is found globally, especially along major bird migratory routes including Africa, Europe, the Middle East, North America, and West Asia.
West Nile Virus: An Overview
The West Nile Virus is an RNA virus borne by mosquitoes. First isolated in a woman in the West Nile district of Uganda in 1937, it was later identified in birds in the Nile delta region in 1953. However, until 1997, WNV was not considered harmful to birds. Over the past fifty years, human infections caused by WNV have been widely reported across many different countries.
Transmission Cycle of the West Nile Virus
Birds serve as the primary host of the virus, with the culex species of mosquitoes acting as the main vector for transmission. Infected mosquitoes transmit the WNV between and among humans and animals. When these mosquitoes feed on infected birds, they too become carriers. The virus circulates in the mosquito’s bloodstream for several days before migrating to the salivary glands. From there, it gets injected into humans and animals during subsequent feeding sessions.
There are alternative transmission routes as well such as from an infected mother to her child, through blood transfusion, or via exposure in laboratories. However, contrary to popular belief, the virus does not spread through consuming infected animals, including birds.
Incidence and Presence of West Nile Virus in India
Tracing back to 1952, antibodies against WNV were first detected in humans in Mumbai. Since then, the virus has been reported in southern, central, and western India. The virus has also been isolated from humans in Karnataka, and from Culex vishnui mosquitoes in Andhra Pradesh and Tamil Nadu. Further, WNV neutralizing antibodies were found in human serum collected from several Indian states.
During an outbreak of acute encephalitis in Kerala in 2013, the complete genome sequence of WNV was identified. In Tamil Nadu, a clear connection was drawn between WNV and eye infections during an epidemic in 2010.
Symptoms and Severe Forms of West Nile Virus
For most infected individuals (80%), the disease presents no symptoms. In the remaining 20% of cases, symptoms can include fever, headache, fatigue, body aches, nausea, rash, and swollen glands. Severe infections can cause neurological diseases like West Nile encephalitis or meningitis, West Nile poliomyelitis, or acute flaccid paralysis. Reports have also surfaced linking WNV with Guillain-Barré syndrome and radiculopathy. Around 1 in 150 cases develop into serious diseases, leading to lasting nervous system damage or even fatality.
Prevention and Control of West Nile Virus
The establishment of an active animal health surveillance system is crucial for detecting new cases in birds and horses. As outbreaks in animals often precede human cases, this serves as an early warning system. Additionally, the European Centre for Disease Control and Prevention recommends that potential blood donors who have visited or lived in an affected area should be subject to deferral or nucleic acid testing.
There is currently no vaccine for WNV available. Treatment focuses on providing supportive care for neuroinvasive WNV patients, helping them manage their symptoms and preventing further spread of the virus.