Question

How has West Nile virus affected California?

Answer 1

West Nile virus (WNV) is a mosquito-borne disease that is common in Africa, west Asia, the Middle East, and more recently, North America. Human infection with WNV may result in serious illness. Experts believe WNV is established as a seasonal epidemic in North America that flares up in the summer and continues into the fall.

West Nile virus first appeared in California in 2002 with the identification of one human case. In 2003, three human cases occurred in California and WNV activity was detected in six southern California counties. By 2004, West Nile virus activity was observed in all 58 counties in California.

• There were 830 human infections of West Nile virus from 23 counties detected in California in 2004.
• Sixty-six of these cases were first detected in asymptomatic individuals through screening done at blood banks - 15 later became symptomatic.
• Of the 779 WNV cases with symptoms, 395 are classified as West Nile fever cases, 289 are classified as West Nile neuroinvasive disease, and 95 are of unknown status.
• There have been 28 West Nile virus-related fatalities to date in California, in Glenn, Kern, Los Angeles, Orange, Riverside, San Bernardino, and Tehama counties.
• According to the California Department of Food and Agriculture, there have been 540 horse infections from 32 counties in 2004.
• Of these West Nile virus infected horses, 228 have been euthanized or died.
• 3,232 dead birds tested positive for WNV in California in 2004.
• West Nile virus infected dead birds have been found in every county in California.
• The top 4 species affected by WNV are 1) American Crows 2) Western Scrub-Jays 3) Yellow-billed Magpies and 4) Steller's Jays
• 1,136 mosquito pools from 18 counties tested positive for WNV in 2004.
• A mosquito pool is a collection of approximately 50 mosquitoes that are tested together for West Nile virus.
• 809 chickens from 22 counties tested positive for WNV antibodies (seroconverted) in 2004.