West Nile Virus in Birds

The West Nile virus is commonly found in Africa, West Asia, Eastern Europe, and the Middle East. It is believed to have arrived in the eastern United States in the summer of 1999.

How is West Nile virus spread?

The West Nile virus (WNV) is transmitted by the bite of a mosquito (primarily Culex species) that is infected with the virus. The mosquitoes become infected after biting birds carrying WNV. The virus circulates in the blood of infected birds for several days prior to the bird dying. 

WNV incubates in the mosquito for 10–14 days before it can be transmitted to another host. Birds, humans, and animals are exposed when the mosquito bites to obtain a blood meal. Birds are susceptible to the virus and act as the host.

Does every infected animal or person get sick?

Not every healthy person, animal, or bird that is bitten by an infected mosquito will develop symptoms of WNV infection. Some birds, such as crows, jays, and raptors (owls, falcons, eagles, hawks, kestrels, etc.) are extremely susceptible to WNV and have been hit hard by it in several areas around North America. Avian pathologists agree that pet birds are susceptible, but less likely to develop disease symptoms. Any exposure to Culex mosquitos has risks. Fatality rates are dependent on the species of bird infected.

What are the clinical signs?

WNV can cause encephalitis (inflammation of the brain). The signs range from elevated body temperature, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis to sudden death. A parrot with a severe WNV infection may become sick very quickly. It may be found on the bottom of the cage or suddenly found dead with few or no warning clinical signs.

There are few documented cases of pet birds with WNV, so there is an incomplete picture of what to expect. Speculation leads us to believe that an infected, susceptible parrot may not show signs of illness at all, as seems to occur in many species of indigenous birds. Birds like robins, sparrows, and finches play a crucial role: they can carry the virus without showing any significant symptoms, acting as “amplifying hosts” that maintain the virus’ presence in the environment.

How can I protect my bird from the virus?

There is no specific treatment once infected with WNV. It is easier to prevent the problem than to deal with it once it has happened. The most effective way to avoid contracting WNV is to eliminate exposure to mosquitoes. If possible, keep your bird indoors during the mosquito season, especially at dawn, dusk, and early evening. Have properly sealed screen windows and keep the doors closed. Mosquitoes can sneak indoors as you come and go.

Be diligent about reducing standing or stagnant water in your immediate surroundings. Old tires, buckets, clogged eaves troughs, puddles, ponds, poorly drained land, ditches, etc., can be ideal breeding grounds for mosquitoes. If it is not possible to eliminate the water, then treat the water with a mosquito larvicide. There are various products that will attract and kill biting insects. Mosquito repellents have not been sufficiently tested for safety on birds and are not recommended at this time.

Is there a vaccine for West Nile virus?

Several vaccines are available for use in horses. Research has shown that, while the vaccine seems to cause little to no harm in some avian or bird species, it has caused serious reactions in others (especially lorikeets and roseate spoonbills). It appears that the vaccine may not stimulate the immune system well enough to produce a protective titer (the antibodies produced against the virus). This means that the vaccine may not effectively protect a bird from exposure to WNV. There may be special cases where it might be in the bird's best interest to vaccinate it with the equine vaccine. These cases include high-risk species such as raptors or birds in high exposure areas.

This is a topic of much concern and ongoing research. Please contact a veterinarian familiar with birds for the most recent information about this important disease.