West Nile virus (WNV) casts a broad net of influence, entwining itself in the mosquitoes that transmit it, the birds that carry it, the animals and people that are affected by it, and the environment it spreads through. But to understand that complex picture, you need to understand the virus itself. Kristen Bernard, DVM. MS, PhD, associate professor in the department of pathobiological sciences at the University of Wisconsin-Madison School of Veterinary Medicine, is using her research to untangle the functions of WNV.

"I’m trying to understand how the virus causes disease," said Bernard. "What I want is to understand each step of what the virus is doing in the body."

The virus, first seen on the east coast in 1999 before spreading rapidly across the United States, is an arthropod (insect)-borne virus. Although not common in Wisconsin, WNV presents a serious threat. The virus cycles between mosquitoes and birds, then spreads when an infected mosquito bites a healthy animal. According to Bernard, some are more affected than others, with humans, horses, and some types of birds hit the hardest.

But the common thread among all these species is one tiny buzzing insect. "In nature, there isn’t any vertebrate to vertebrate transmission," Bernard said. "You need to have that mosquito