UC Davis Scientists Targeting Crows in War Against West Nile virus

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DAVIS, CALIF. - 9/8/06 - Corvids, including American crows, Yellow-billed Magpies, Western scrub-jays and other members of the Corvidae family, serve as the primary reservoirs or incubators for the mosquito-borne virus, according to research entomologist William Reisen of the Center for Vectorborne Diseases (also known as CVEC), a unit of the UC Davis School of Veterinary Medicine.

"Communal crow roosts help drive the West Nile virus into the Culex (mosquito) populations--that's why it's so important for people to find and report dead birds," said Reisen, a professor with the Department of Pathology, Microbiology and Immunology at the UC Davis School of Veterinary Medicine. "Crows are good hosts for mosquitoes. There's an amazing amount of virus in the bloodstream of infected crows, sometimes as much as 10 billion virus particles in one millimeter of blood. They're like a big sack of virus."

Reisen and his research team are targeting crows in work funded by the UC Mosquito Research Program (UCMPR), Sacramento-Yolo Mosquito and Vector Control District (MVCD), and the National Institutes of Health. CVEC works closely with UCMRP, the UC Davis School of Medicine and the UC Davis College of Agricultural and Environmental Sciences.

"We're investigating how the distribution of host-seeking mosquitoes and infected corvids intersect in time and space to effectively amplify the West Nile virus in an urban California landscape," said Reisen. "We're studying how landscape features, mosquito abundance patterns and corvid roosts affect the distribution and abundance of West Nile virus in Davis."

Collaborator Carrie Nielsen, a UC Davis doctoral candidate in epidemiology, said the research includes work on the vector (Culex mosquitoes), the host (birds, but especially corvids) and incidental hosts (humans and horses).

Reisen said Southern California's WNV epidemic appears to be subsiding because most of the crows have died or are immune. He said he expects the transmission to intensify in the Central Valley, driven by American crows and Western scrub-jays. His research indicates that crows are a common host for the virus in urbanareas and that scrub jays are a common host in rural and desert areas.