Mosquitoes could have carried West Nile Virus Across U.S.
Mosquitoes – not as suspected bird – could have played a major role in spreading West Nile virus westward across the United States, according to a study by researchers at the Johns Hopkins Bloomberg School of Public Health. The study is among the first to examine the role of mosquitoes in the spread of West Nile virus in the U.S. and published in the March 2 edition of Molecular Ecology.West Nile Virus was first detected in the U.S. in 1999 in New York. Between 2001 and 2004, the virus spread rapidly across the U.S., making a great leap across the Mississippi River and the Great Plains, between 2001 and 2002. The birds are known hosts of the disease and were suspected of carrying the virus around the continent. It can transmit the virus to certain mosquitoes, including Culex tarsalis, which can transmit the disease to humans through their bites.“In the past, people believe that birds played the major role in spreading West Nile. However, the rapid spread of West Nile did not follow a pattern of leapfrog move north or south along Route migratory birds, as expected, “said lead author Jason L. Rasgon, PhD, assistant professor in the Bloomberg School of the Malaria Research Institute and the W. Harry Feinstone Department of Molecular Microbiology and Immunology. “When you see movement so fast, one of the main questions we ask is:” What are the factors that mediated this jump? “Our study shows that mosquitoes are a likely candidate.”For the study, Rasgon and his co-author, Meera Venkatesan, a former graduate student at the Bloomberg School and currently a postdoctoral researcher with the Center for Vaccine Development and Howard Hughes Medical Institute, analyzed DNA from mosquitoes collected from 20 sites throughout the western U.S. Genetic analysis identified three distinct groups of populations of C. tarsalis. They found the gene flow between large populations, suggesting a general movement by mosquitoes. However, gene flow was limited in certain regions such as the Sonoran Desert of Arizona, the Rockies and east of the plateau of High Plains, the three of whom appear to have blocked the movement of mosquitoes. The researchers also found that the genetic pattern of the group was consistent with the pattern of infection with West Nile virus in the U.S.“People have the idea that mosquitoes do not move much. Certainly it is true that mosquitoes. But the range of this mosquito in particular is as great as the variety of birds than originally thought to move the virus,” Rasgon said.