Margaret A. Wissman, DVM
Learn about the causes and symptoms of West Nile Virus from this 2012 video.
In 1999, West Nile Virus (WNV) was first discovered in humans, dogs, cats and horses in New York. By the next summer, birds were literally falling out of the sky, succumbing to a virus that they had no immunity against. This virus, which is transmitted by the bite of infected mosquitoes, began spreading throughout the United States. Cases were discovered in Connecticut and New Jersey. Year by year, it has spread throughout the United States.
What exactly is West Nile Virus? This is a virus, in the group of Flaviviruses, first identified in Uganda in 1937, but it has been around for more than a thousand years. West Nile Virus is one of more than 70 viruses in the group, with the majority being transmitted by mosquitoes or ticks, and includes dengue fever, yellow fever virus and St. Louis encephalitis virus. Birds are the natural reservoir, and mosquitoes transmit the disease when they bite a bird and infect the bird with a large viral load.
Many birds that are infected do not become ill at all in Old World countries. Animals that have been identified as being affected by WNV include humans, birds, horses, dogs, cats, bats, chipmunks, skunks, squirrels, nonhuman primates and domestic rabbits. Other animals may also become infected that have not yet been confirmed. The virus circulates in natural transmission cycles involving primarily the Culex species of mosquitoes and birds; humans and other mammals are thought to be incidental hosts.
WNV was a new virus to the United States, so many of our native and established wild birds often became exposed, many became ill and many died acutely, as did some exotic pet birds, often with neurological signs.
A seriously infected bird may die very quickly with no clinical signs before death, or it may be discovered moribund on the bottom of the cage. Some infected birds develop neurological signs, and may sit quietly or press their heads against the bars of the cage, or may even develop seizures.
There are several tests available to detect WNV in birds. Titers of the bird’s serum may show an elevation of antibodies against the virus, but often two titers must be evaluated a few weeks apart to look for a rise in the titer, indicating an active infection. Vaccination against WNV may cause an inaccurate interpretation of the test results. A very specific test, called a DNA PCR test, is also useful in detecting evidence of the actual virus from live birds (using spinal fluid or blood) or from birds or animal that have died, testing the spinal cord, brain or kidney for the presence of the virus.
Keep your bird inside or in a mosquito-proof area during peak mosquito hours.
In addition to specific testing, other tests can be helpful in the diagnosis of a virus. Often when a bird has a virus in the bloodstream, the overall white blood cell count (WBC) is lower than normal and the percentage of the two most common types of white blood cells is inverted. Other tests, such as radiographs or different blood tests, may also be performed to assess the bird’s overall condition and health.
There is no specific treatment for WNV, should it be diagnosed in a bird. While there are some antiviral medications available for people, these have no effectiveness against WNV. Support care can be beneficial, including gavage feedings, parenteral fluids, warmth, antibiotics and/or antifungal therapy for any secondary infections or other medications deemed necessary.
Some nutrients can be provided as supplements, which can help support or stimulate the immune system. Specific amino acids and nucleotides can provide a sick bird with building blocks for healing and repair. In my experience, a nutraceutical called dimethylglycine (DMG) has been found to be beneficial to birds suffering from viral, bacterial or fungal diseases, as it helps the immune response. I believe this nutraceutical also provides excellent support for the nervous system, which can be beneficial when dealing with WNV.
Some birds may be infected with WNV and never become clinically ill; others may show mild signs of illness and yet others may end up being fatally infected. During the first few years after it was discovered, many crows and other species of wild birds were found dead in areas of outbreaks, but this disturbing group of deaths has tapered off dramatically. The anticipated epidemic that we worried about when WNV first arrived on our shores hasn’t really occurred.
It is not possible for a person to catch WNV from touching a dead bird; however, care should be be taken when handling any deceased birds found outdoors, and gloves should be worn to avoid touching dead birds directly. Also, WNV is not passed person to person other than through surgical transplantation of infected organs from an infected human donor, or potentially through contaminated blood products, although this is unlikely due to the screening of blood and products.
Some birds may be infected with WNV and never become clinically ill; others may show mild signs of illness and yet others may end up being fatally infected.
Mosquito larvae thrive in standing water. Ponds, birdbaths, fountains, empty flower pots, old tires and clogged rain gutters can all become fertile breeding grounds for mosquito larvae. Check around your property for items that might contain standing water and either remove them, turn them over or drain them.
You can also add chemicals to standing water that will kill mosquito larvae. Insecticides and natural predators can also minimize mosquito populations. Keep in mind that it is easier to eradicate mosquito larvae than it is to attempt to do the same for adult mosquitoes.
Certain fish consume mosquito larvae. But before releasing any live animals into a pond on your property, find out if this is legal. You can also add an aerator, fountain, waterfall or spitter to your pond to help prevent it from becoming a breeding ground for mosquitoes.
Most mosquitoes are active at dawn and dusk, so keep your birds indoors during those times. Any outside area for your bird must have mosquito-proof screening around it. Try gardening with some plants that are known to help repel mosquitoes, including citronella, lavender, basil, catnip, pennyroyal and marigolds.
I don’t recommend using mosquito repellent on a bird’s skin. Be as diligent as you can to prevent mosquitoes from being able to access and bite your birds. During the summer, don’t allow doors to remain open for any length of time. Make sure screens on your windows are tight-fitting and don’t have any holes. Mosquitoes have a hard time finding a suitable place to bite most birds, because feathers are difficult to bite through.
Birds are more likely to be bitten on bare facial skin or on the legs, although again, scales are more difficult for mosquitoes to bite through. Birds that feather pick and have bare patches are more likely to be bitten on the denuded skin.
The vaccine against WNV that has been developed for horses can be used in special situations to vaccinate birds at high risk for WNV. Some studies have shown that birds have not developed protective antibodies against the virus after vaccination, however.
Even if a mosquito gets through your defenses, the chances are that your bird won’t contract a serious case of WNV. But, as always, if you are concerned, contact your avian veterinarian for advice.
Don't have any standing water on your property. Still water is a mosquito-breeding ground waiting to happen.
Mosquitoes are active during dawn and dusk. Keep your bird inside during these times, or in a mosquito-proof area.
Keep your home or bird's aviary with mosquito-proof screening.
Plant flowers that repel mosquitoes, such as lavender, basil, catnip or marigolds.
Want to learn more?
Outdoor Safety For Birds
How To Create A Safe Bird Aviary