Small songbirds succumb to West Nile virus

When diseases hit wildlife, finding hard evidence that the pathogen is killing animals can be tough. For example, researchers suspect that West Nile virus is behind population declines in some small songbirds but haven’t found many dead infected birds.

Now, a study in Biological Conservation has turned up new evidence for the virus’ lethal effects. The team caught mosquitoes, which transmit West Nile virus, at seven sites in Maryland and Washington, DC and tested the blood meals carried by the insects. The researchers also took blood samples from songbirds captured at those sites. In the lab, they infected birds with the virus.

The mosquitoes had bitten Carolina wrens, northern cardinals, and tufted titmice at three to seven of the sites, the team reports. The birds’ blood tests suggested that 18 percent of the wrens, 35 percent of the cardinals, and 2 percent of the titmice had been exposed to the virus.

About a quarter of the wrens infected in the lab died, as did all of the infected titmice. The surviving wrens still carried the virus four weeks after infection. West Nile virus “may be killing many small-bodied birds, despite the absence of large numbers of dead birds being observed and testing positive for WNV,” the authors write. Roberta Kwok | 5 July 2013

Source: Kilpatrick, A.M. et al. 2013. Predicted and observed mortality from vector-borne disease in wildlife: West Nile virus and small songbirds. Biological Conservation doi: 10.1016/j.biocon.2013.05.015.

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