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 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