West Nile Virus

West Nile virus (WNV) belongs to the family of viruses which includes Japanese encephalitis, St. Louis encephalitis, and Murry Valley encephalitis. These are also called arboviruses, i.e. arthropod-borne (insect) and is primarily transmitted by mosquitoes.

It was first isolated in the West Nile District of Uganda in 1937 and is widespread in Africa, Europe, and Asia. It was first detected in the United States in 1999 in New York City. WNV was responsible for many human cases and several deaths during that year. Since then, WNV has spread westward accros the U.S. increasing the number of humans which have been affected.

Mosquitoes cannot acquire the virus from dead-end hosts such as humans and horses. Culex tarsalis and Culex quinquefasciatus are the most likely transmitters of WNV in New Mexico. Crows and jays are highly susceptible to WNV and are indicators of potential human exposure. Horses are very susceptible to WNV and may contract the disease upon the bite of an infected mosquito. The incubation period is 5 to 15 days and symptomology may include stumbling, muscle weakness, partial paralysis, fever, convulsions, coma, and death. Once symptoms appear, the fatality rate can be as high as 40% in unvaccinated horses. A vaccine is available to protect horses from WNV.

For more information about other aspects of the City's Vector-Borne & Zoonotic Disease Division program, please call 505-452-5300