West Nile (WN) virus belongs to a large group of viruses called Arborviruses.

Arborviruses (arthropod-borne virus) are most commonly spread by blood sucking insects. In the United States the mosquito is mainly responsible for the spread of the virus, but in other parts of the world ticks can spread it as well. WN is further classified within the arborvirus group as a flavivirus. Other virus in the flavivirus family are St. Louis encephalitis, Japanese encephalitis, Yellow fever and Dengue fever.

WN virus was first identified in 1937 in the West Nile district of Uganda, hence its name. It has caused outbreaks of illness in humans in Europe, Africa and Asia. It typically cycles between birds and mosquitoes, and migratory birds have been suggested as the source of virus where introduced. This virus has not been previously seen to cause significant disease or death in birds.

In 1999, there was an outbreak of human and avian illness/death in New York City. The outbreak was initially attributed to St. Louis Encephalitis, until it was correctly identified as WN virus through testing at the CDC. Prior to then, this virus had not been seen in the western hemisphere. Since then, it has spread and is now reported as far south as Florida and as far north as Ontario. The spread is being tracked by a combination of wild bird, human, veterinary, mosquito and sentinel flock surveillance.

The strain of West Nile (WN) virus that has emerged here in the United States causes significant mortality in birds and the recommendations are to take precautions to protect your companion birds.

"It is clear that raptors, psittacine birds, and several other groups are susceptible to mortality from WN virus. To protect birds from infection owners will need to consider precautions. Mosquito proof enclosures, monitoring mosquito abundance through routine trapping, and adult and larval mosquito control will need to be considered, in private and public settings. We have seen that mosquitoes carrying WN virus may enter homes and buildings and infect birds, so intact screens on aviary windows and doors are important for the protection of indoor birds." ¹

1.West Nile Virus 2000: Surveillance Summary and Implications fro Avian Medicine; B. Cherry, VDM PhD; Proc Annu Conf Avian Vets 2001; p5.

Further information on the West Nile Virus, including updates on its spread, can be found at the CDC site.