West Nile Virus

Vets and Flamingo Photo
WCS Bronx Zoo veterinary staff vaccinate a Caribbean flamingo chick against the West Nile virus.
Julie Larsen Maher ©WCS

West Nile virus (WNV) first appeared in Uganda’s West Nile District in 1937. An outbreak in Israel in 1957 demonstrated the virus’s ability to cause fatal encephalitis in elderly humans. Spread by mosquitoes and blood transfusions, the virus can cause deadly brain inflammation in horses and birds.


West Nile virus did not appear in the Western Hemisphere until summer 1999. At that time, a few people and an unusually high number of wild crows began dying from unknown causes in the New York City region. Zookeepers at the Queens Zoo were the first to notice the unusual number of deaths in crows. Numerous bird species at the WCS zoos—including two Chilean flamingoes, an owl, and an eagle—as well as horses in the area also became ill and died due to what appeared to be a new and emerging disease.

What WCS is Doing

WCS pathologists were critical to unraveling the mystery surrounding West Nile virus. Recognizing the pattern of disease in affected birds and suggesting a connection between the disease outbreak in birds and people, our pathologists drove investigations that ultimately proved West Nile virus was the culprit and that the virus had been newly introduced into the United States.

A virus isolated from one of our flamingos contributed to the development of a West Nile virus vaccine for horses. WCS veterinarians were among the pioneers to administer this vaccine to birds. WCS health staff shared our vaccination information and vaccine protocols with others through presentations and publications. Our broad vaccination program resulted not only in saving the lives of hundreds of birds within WCS parks but also birds in zoos and aquariums throughout the country.

~/media/Images/wcs org/forms/please donate to help conservation.png
Stay in touch with WCS and receive the latest news.