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It’s a deadly disease that could be heading to California, and it isn’t SARS. 

The West Nile Virus, a mosquito-borne disease, appeared in New York City in 1999 and has spread further west every summer. 

“It takes over about a quarter of the country every year,” said William Hamersky, environmental specialist for the Alameda County Mosquito Abatement District. “That’s the scary part.” 

But experts say Berkeley, Oakland and San Francisco may not be hard-hit by the virus, which killed 284 Americans last year. 

“This is a safe area,” said UC Berkeley epidemiologist William Reeves, explaining that cool temperatures and effective control measures have limited the local mosquito population. “Be happy you live in Berkeley.” 

Still, Reeves warns that an infected traveler arriving on an airplane or a migrating bird that carries the disease could create a local problem. 

Blood transfusion is also a danger. Doctors reported in September that the virus could be transmitted via donated blood, and since then there have been 21 confirmed cases across the nation, with six deaths. 

“I think it does pose a risk,” said UC Berkeley epidemiologist Arthur Reingold.  

In recent months local companies Roche Diagnostics of Pleasanton and Chiron Corporation of Emeryville have scrambled to develop and ship West Nile Virus tests to the nation’s blood banks.  

The U.S. Food and Drug Administration wants all donated blood screened for West Nile Virus by July 1. Becky O’Connor, spokesman for American Red Cross Blood Services for Northern California, which supplies 23 East Bay hospitals including Alta Bates Summit Medical Center in Berkeley and Oakland, said her blood bank will meet the July 1 deadline with a test developed by Chiron. 

“In the meantime, until the test is available, unfortunately, we are not able to test for West Nile Virus,” she said. 

O’Connor noted that West Nile has not yet hit California, where the Red Cross gets 70 percent of its blood for local use. The remaining 30 percent, she said, comes from surrounding states.  

O’Connor said the chances of receiving infected blood are slim and that patients in need should not hesitate to get a transfusion before July 1. 

“The benefits far outweigh the risks,” she said.  

West Nile is a “flavivirus” commonly found in Africa, West Asia and the Middle East and is closely related to the St. Louis encephalitis virus found in the United States. 

Mosquitoes spread the disease by biting an infected animal — usually a bird or horse — and passing the virus to a human or another animal.  

Most people infected with West Nile Virus do not have any symptoms, but about 20 percent develop a fever, headache or body aches. About one in 150 come down with more severe symptoms, including encephalitis, a life-threatening swelling of the brain. 

Last year, West Nile Virus infected 4,156 Americans, including one Californian in Los Angeles, according to the U.S. Centers for Disease Control and Prevention (CDC). There have been no human cases yet this year. 

The virus tends to appear in late summer, but the death of an infected Minnesota horse in early May has stoked fears that the disease could hit earlier this year. 

Experts say California, with some 52 mosquito abatement districts around the state, is in a good position to handle the West Nile threat, whenever the virus arrives. 

“Frankly, California has been at the leading edge of mosquito abatement,” said Reingold. “This state is generally much better prepared for this than other states.” 

Reeves said the state has a long history of battling mosquitoes that goes back to malaria control efforts begun in 1904. California has also reined in St. Louis encephalitis and western equine encephalitis, both of which peaked in the 1950s, Reeves said. 

“We’re using the same surveillance system that we’ve had for western and St. Louis and they’ve been very effective,” he said. 

The city of Berkeley has joined the fight through a public education campaign that includes pamphlets, articles in a quarterly newsletter and press releases published on the city’s Web site. 

Experts are warning all Californians to take precautionary steps — wearing long sleeves, using insect repellent and eliminating stagnant pools of water, like those in old tires and bird baths, that serve as breeding grounds for mosquitoes.