MicrobeWorld

Every year as the days grow warmer, the Eastern equine encephalitis virus (EEEV) reemerges along the eastern coast of the United States, where it causes devastating disease in horses and, more rarely, humans. Scientists have long wondered how the virus, which is transmitted by the bite of an infected mosquito, survives the cold, mosquito-killing North American winters. Now, a new study suggests that snakes harbor the virus through the winter, but experts disagree on whether the finding clinches the question for good.

"This is very, very impressive work," says Scott Weaver, a virologist at the University of Texas Medical Branch in Galveston, who has worked extensively on EEEV but was not involved in the study. "It makes a very strong case that snakes play an important role in maintaining the virus."

EEEV is deadly: Anywhere between 60 and 712 horses have been infected with the virus each year since 2003, according to U.S. Department of Agriculture statistics, and most infected horses die. Human cases are rare, about five to 10 cases a year, but 35% to 50% of those with the disease die, and more than a third of its survivors have lasting neurological damage. Most cases are concentrated along the Gulf Coast and Eastern Seaboard.