West Nile Virus Kills Bald Eagles

At least 27 bald eagles have perished in Utah in recent days in an unusual outbreak of West Nile Virus. Five other bald eagles are recovering in rehabilitation centers. Wildlife officials noted that the West Nile outbreak is unexpected at this time of year, considering the main vector, mosquitoes, are typically inactive during the cold winters in Utah. Between 750 to 1,200 bald eagles migrate to Utah annually during the winter.

Mosquitoes carry a virus that causes West Nile infection. The West Nile Virus is a member of the flavivirus genus, which also includes Yellow Fever and Dengue Fever. West Nile is potentially fatal to humans and causes severe neurological diseases in humans. Humans most often become infected through mosquito bites. Mosquitoes themselves become infected when they feed on infected birds, which are the natural hosts of the virus. No human to human transmission of the virus has been documented according to the World Health Organization.

In Utah the eagles are believed to have gotten sick from eating infected eared grebes, a type of bird, living around the Great Salt Lake.Thousands of the eared grebes have died since November. At first, an infectious bacterial disease was thought to be the killer but new reports published on the 31st of December revealed West Nile to be the actual cause of death. The West Nile Virus is pretty hardy compared to other viruses. It can survive for a few days in the carcasses of infected birds. Predatory birds, such as the bald eagles, who feed on the dead birds become sick. A Utah Health Department epidemiologist says that the dead birds do not pose a threat to humans, however people who find sick or dead birds should refrain from handling them.

Each year more than two million of the eared grebes visit the Great Salt Lakes area during their winter migration from Canada and states west of the Mississippi River. Luckily for the eagles the eared grebes are supposed to leave the Great Salt Lake in January on their way to Mexico and the Southwestern U.S. The eared grebes' exodus should reduce the risk of disease for the eagles.

Since West Nile Virus's 1999 arrival in the United States, multiple bird species have been affected. The National Wildlife Health Center reports that West Nile Virus has been identified in over 225 different wild and captive bird species (for a list click here). Studies have shown that several bird populations have declined due to West Nile. Up to 45% of crows perished after the virus's arrival, while robins, chickadees, and eastern bluebirds have faced similar declines. Along with climate change and habitat loss, West Nile is another threat facing our nation's bird populations.

References:

Minard, A. "West Nile devastated U.S. bird species." National Geographic. May 16, 2007.

Silva, D. "Soaring deaths of bald eagles in Utah attributed to West Nile virus." NBC. December 31, 2013.

West Nile Virus. World Health Organization, 2014.

West Nile Virus. Mayo Clinic, 2014.

Zuckerman, L. "West Nile virus blamed for death of eagles in Utah." Yahoo. December 31, 2013.

Images:

Paul Friel (via Wikimedia).

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