WestNilevirus

West Nile virus (WNV) is an enveloped, positive-sense RNA virus in the genus Flavivirus, family Flaviviridae. It is primarily transmitted by mosquitoes and can infect birds, humans, and horses. The virus circulates in a natural cycle between birds and mosquitoes, with humans and horses acting as incidental hosts.

The natural transmission cycle features birds as the main reservoir. Infected mosquitoes acquire the virus from birds and can transmit it to other birds, as well as to humans and horses. Humans are typically dead-end hosts and do not sustain transmission cycles.

WNV was first identified in 1937 in the West Nile district of Uganda. Since then it has caused outbreaks across Africa, Europe, the Middle East, and Asia, and it entered the Americas in 1999, appearing in New York and rapidly spreading across North America.

Clinical presentation varies. Most infections are asymptomatic. About 20 to 25 percent develop West Nile fever, a febrile illness with headache, malaise, myalgia, and sometimes a rash. A small minority develop neuroinvasive disease, including meningitis, encephalitis, or acute flaccid paralysis, with greater risk in older adults and individuals with weakened immune systems.

Diagnosis relies on detecting West Nile virus–specific IgM antibodies in serum or cerebrospinal fluid, supported by molecular tests such as RT-PCR in the acute phase. There is no specific antiviral treatment; care is supportive, with hospitalization for severe cases.

Prevention centers on mosquito control and personal protection to reduce bites. There is no approved human vaccine as of now; vaccines exist for horses, and several human vaccine candidates have been investigated. Public health measures emphasize surveillance, vector control, and public education.