On the other hand, the distribution of horses may not reflect human population density closely enough for accurate assessment of risk of human disease. It had been thought that the virus was only transmitted through mosquito bites. The infected birds died five to eight days later. Most of the healthy birds, the researchers found, also became ill from the virus and died five to eight days after the first infected bird died. It confirms a suspicion that we had and wanted to verify, said Dr. Robert McLean, director of the USGS National Wildlife Health Center.
Mosquitoes are the primary means of transmission of the virus between birds and to humans.
But this certainly opens up a host of new questions. Chief among the questions, McLean said, is exactly how the virus moves from bird to bird. He said he and other scientists are working on that question now. We know that crows are highly susceptible to the virus and that they are more likely than other bird species that live in close contact with one another to transmit the disease to other crows, he said. We know that the virus attacks the crow s entire body and often affects all the major organs.