West Nile Virus: Transmission In Birds

August and September are the heart of West Nile Virus season; reported infections nearly triple in a matter of weeks. Yet many don’t realize that West Nile Virus is highly infectious in birds – more than in humans. Furthermore, birds play a much larger role in spreading the disease than people realize.

West Nile Virus sounds scary, but it doesn’t affect humans as much as you might think. Only 96 people in the District of Columbia have been diagnosed with West Nile Virus in the last 15 years, according to data collected by the CDC. Maryland and Virginia have showneven less incidence among their larger populations (about 1 infection per million people). In fact, 70%-80% of people infected with West Nile Virus never show any symptoms.

This Barred Owl came to City Wildlife having difficulty walking and flying. After a few days of observation, we diagnosed it with West Nile Virus. The owl made a full recovery.

Birds are more widely affected by West Nile Virus. Symptoms in birds include many things, but the most common symptoms include lethargy, weakness, uncoordinated walking or flying, anorexia and weight loss. In severe infections, birds can have seizures indicating inflammation in the brain and spinal cord. Most of these infections lead to death.

Infection rates vary by species. Corvids (crows, ravens jays and magpies) are the most susceptible; some experiments showed a 100% mortality rate in infected species of American Crows and Blue Jays. The virus progresses very quickly in these species, often killing them before severe neurological symptoms set in. Other species like pigeons, geese, ducks, and chickens seem to have a higher tolerance for the virus.

However, birds infected with West Nile pose a threat to species other than themselves. In bird species, the virus builds up in the blood to much higher concentrations than in humans and other mammals. Like humans, most birds infected with West Nile do not show symptoms, but increased levels of West Nile in birds make them “amplifier hosts”.  This means mosquitos can become transmitters by biting an infected bird, and in turn, this increases the amount of mosquitos that can transmit the virus.

West Nile Virus incidence in humans is generally decreasing, but without continued measures to control it, West Nile incidence could rise again. So what can you do to help prevent the spread of West Nile Virus?

Local governments usually handle mosquito control measures. These measures prevent West Nile Virus and other mosquito-borne diseases, notably the Zika virus. Contact your local health department to learn what is being done in your own community.

Be sure to report any dead birds you may find to your health department as well. Some studies have shown that dead birds infected with West Nile can transmit the virus, especially to crows and other scavengers that may eat dead birds.

The transmission and spread of West Nile Virus is another reminder of how connected we are to the environment around us. Even when it seems like humans are singularly affected, it is likely that we aren’t.

For more information, be sure to check out the CDC’s website. They have lots of helpful information on everything you need to know about West Nile Virus.