Study Might Link American Robins to West Nile Virus

A recent DNA study of the blood consumed by 300 mosquitoes in Connecticut over the past three years found that 40% of them fed on American robins (Turdus migratorius), while only 1% fed on American crows (Corvus brachyrhynchos). Theodore Andreadis, MS, PhD, from the Connecticut Agricultural Experiment Station, led the study. He turned his findings over to the Centers for Disease Control and Prevention in Atlanta, Ga.

Because of these findings, some people are wondering if crows are still major factors in West Nile virus (WNV) transmission. Bob McLean, PhD, research program manager of wildlife diseases at the National Wildlife Research Center in Fort Collins, Colo., admits his researchers have been interested in robins for a long time because robins are a good host for the closely related St. Louis encephalitis virus, but feels crows will remain key players in the viral chain.

"Crows play a different role [in WNV transmission] than robins, and they're going to continue to play a role," McLean said. "Most people think because crows die, they're not contributing to transmission. Before they die, crows can circulate huge amounts of virus in their blood for three to four days and infect many mosquitoes--possibly way more than even robins. Despite the low percentage of mosquitoes found feeding on crows in this study, crows are obviously being fed on by many infected mosquitoes because so many crows are dying of WNV infection each summer. Crows are still very important and will remain a risk for local transmission."

Some researchers feel it is too early in the process to prove the robin's place in WNV viral amplification (whether they are good viral hosts or not). Agreeing with Andreadis, McLean feels the next step is to analyze the robins more closely.

"We need to capture the birds and look for, in this case, not mortality but antibodies," McLean said. "Finding out how many birds are exposed to the virus will give us better clues if they are good viral hosts."

While Andreadis' research brings scientists closer to understanding WNV, McLean feels the next step should be to locate what triggers early virus transmission. "The biggest key is to go after what initiates the transmission of WNV every year," McLean said. "That's why our emphasis is on understanding the transmission system, locating the weak points in the sequence. We're learning as we go along, so research of this nature is very helpful."

Researchers are urging people to continue protecting themselves and their animals from mosquitoes just as strongly as they have in the past. Mosquitoes are still the bridge carrying the virus to humans.


About the Author

John V. Wood

John V. Wood is an Emmy Award-winning journalist, and now teaches his craft to high school students in North Carolina. Wood has been published in numerous national magazines/newspapersover his career, and published his first book in June 2010. Wood currently lives in Willow Spring, NC.

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