West Nile Virus

West Nile Virus Activity

Confirmed Cases
in California
2010 YTD vs 2009 YTD

As of 10/19/10

(2010 YTD-Year to date corresponds to the
same time last year)
2009 YTD 2010 YTD
# of Counties 42 35
Human Cases 97 93
Horses 17 19
Dead Birds 504 401
Mosquito Samples 1056 1294
Sentinel Chickens 436 277
Squirrels 10 21

What is West Nile Virus?

West Nile virus (WNV) is a potentially 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. WNV season runs June 1-Nov. 1.

How WNV IS Spread to Humans?

WNV virus is transmitted to humans and animals through a mosquito bite. Mosquitos become infected when they feed on infected birds. Human-to-human transmission of WNV does not occur. However, human WNV infections have been associated with blood transfusions and organ transplants.

Control Activities in Alameda County

West Nile Virus activity in California was very mild in 2010. Alameda County had no human cases of WNV. Only one bird tested positive for WNV; no squirrels or mosquito pools tested positive.