MOSQUITO- AND BIRD-BORNE DISEASE IS HEADING TO CALIFORNIA.

Byline: Staff Writer

After two straight summers of rapid westward movement, the West Nile virus is poised to complete its sweep of the continental United States and arrive in California this year. State health officials are bracing for the mobile virus, which is transmitted by mosquitoes and caused 284 deaths nationwide in 2002.

Just in time for mosquito season, blood banks around the country inaugurated a screening test to detect the virus in the first week of July. Around the same time, the first confirmed case of West Nile virus for 2003 was reported in South Carolina. While the virus has not been detected in California this year, West Nile activity is expected to peak in mid-August and September.

``We've had three years to prepare while the rest of the country has been hit,'' said Evelyn Tu, West Nile surveillance coordinator for the California Department of Health Services.

Detection efforts include tests on dead birds, mosquito pools and horses. Sentinel chicken flocks placed strategically around the state are checked every two weeks. Human cases of viral encephalitis and aseptic meningitis are reported and investigated.

California did have one inexplicable and isolated case of West Nile in Los Angeles County in 2002. So far, the state's stepped-up surveillance efforts have not detected the virus in the mosquito or bird populations. Birds, particularly the crow and jay, have been highly susceptible to West Nile. Mosquitoes typically become carriers by feeding on a bird infected with the virus.

Officials say the likelihood of people falling ill after being bitten by an infected mosquito remains very low - less than 1 percent. In about 20 percent of people infected with the virus, West Nile causes headaches, fever, body aches, nausea, vomiting and a skin rash. Encephalitis and meningitis develop in 1 out of 150 cases, according to the Centers for Disease Control and Prevention.

Dry heat helps

California's dry climate isn't considered conducive to mosquito-borne diseases. But climate is not the key factor that concerns Thomas Scott, director of the mosquito research laboratory at the University of California, Davis. What worries Scott is a particular species of mosquito called Culex tarsalis, common in rural areas of California. In the lab, Culex tarsalis has proven to be proficient at transmitting West Nile to other hosts. Worse, the mosquito also passes on the virus to its offspring.

``They transmit the disease more effectively than any mosquito in North America,'' Scott said. ``If the virus is introduced, it will get into that mosquito. There could be high levels of transmission.''

There are an estimated 200 species of mosquito in the United States and more than 2,500 worldwide, according to the American Mosquito Control Association. More than 30 different mosquito species carrying West Nile have been identified in North America. West Nile's ability to infect numerous species of mosquitoes and birds has fueled its rapid movement, said Dr. Rachel Civen, a medical epidemiologist with the Los Angeles Department of Health Services.

In the United States, West Nile first emerged in New York in 1999. By the end of 2001, the virus had spread as far west as Iowa, Missouri, Arkansas and Louisiana. By the end of 2002, only Oregon, Nevada, Utah and Arizona remained free of the virus.

Mystery case

In 2002, the CDC reported 4,156 confirmed cases of West Nile, including that of a 31-year-old woman from Inglewood. The lone Los Angeles County case stumped investigators. They still do not know how she contracted the virus, Civen said.

``She had no travel history,'' Civen said. ``We did a thorough environmental investigation with mosquito control. We trapped mosquitoes. We even had sentinel chickens on her work route and close to her home. It's a mystery.''

Though the risk of contracting West Nile through blood transfusion is slight, health officials moved to create a screening test that was implemented in early July by blood banks nationwide. Blood banks are now using a nucleic acid amplification test to screen for the virus. After scientists confirmed that 23 cases of West Nile infections could be traced to blood-product transfusions, it became critical to develop and implement the test before the summer mosquito season, said Dr. Steven Kleinman, chairman of the Transfusion Transmitted Diseases Committee for the American Association of Blood Banks.

``We had a target date in mind - and everyone pulled out all the stops,'' Kleinman said.

Previously, clinical tests looked for antibodies formed by the human body. But a person could be infected for 14 to 28 days before producing those antibodies, said Dr. Ross Herron, American Red Cross medical director for blood services for Southern California. The nucleic acid amplification test detects the genetic material of the virus. Donated blood already is screened for HIV, hepatitis B and hepatitis C, among other diseases.

``The risk of West Nile is low enough, so if transfusion is medically indicated, people shouldn't be worried,'' Kleinman said.

Public health officials also are encouraging Californians to take precautions. When outdoors, wear pants and long-sleeved shirts. Use insect repellent containing DEET. Avoid going outside when mosquitoes are most active - at dawn and dusk. Clear any areas of standing water where mosquitoes can breed. And make sure doors and windows have tight-fitting screens. There's no need to invest in expensive measures such as mosquito traps, said Tu from the state health department.

`'Just take the basic preventive measures,'' Tu said. ``There's no need to go out and spend a lot of money. Prevention and precaution are the main things.''

Staff writer Lisa M. Sodders contributed to this report.

Mariko Thompson, [phone] mariko.thompson(at)dailynews.com

West Nile facts WHAT IT IS: A flavovirus that has been found in Africa, West Asia, and the Middle East. In the United States, it was first detected in New York in 1999. The virus can infect humans, birds, mosquitoes, horses and some other mammals. HOW IT SPREADS: West Nile is transmitted to people and animals by infected mosquitoes. A mosquito typically becomes infected by feeding on a bird with the virus. SYMPTOMS: Most people infected with West Nile don't experience any symptoms. But for those who do contract signs of the flu-like illness, they may experience fever, headache, nausea, body aches, mild skin rash and swollen lymph nodes. In 1 in 150 cases, patients will develop encephalitis or meningitis. The elderly are at greater risk for developing a severe case of West Nile infection. SURVEILLANCE: The dying off of birds, particularly crows and jays, can be a sign that the West Nile virus has struck. If you come across a dead bird, don't touch it. Report the sighting to the California Department of Health Services at its toll-free number, (877) WNV-BIRD. They will collect the bird and test for West Nile if appropriate. PREVENTION: Public health officials say basic preventive measures will reduce the risk of infection. -- When outdoors, wear pants and long-sleeved shirts. -- Use insect repellent containing DEET. -- Avoid going outside when mosquitoes are most active - at dawn and dusk. -- Clear any areas of standing water where mosquitoes can breed. At least once a week, empty water from flowerpots, bird baths, swimming pool covers, pet bowls and other places where water collects. -- Make sure doors and windows have tight-fitting screens. For more information on West Nile: Los Angeles County Department of Health Services www.lapublichealth.org/acd/VectorWestNile.htm California Department of Health Services www.westnile.ca.gov Centers for Disease Control and Prevention www.cdc.gov/ncidod/dvbid/westnile/index.htm Sources: Centers for Disease Control and Prevention and California Department of Health Services

CAPTION(S):

3 drawings, photo, box

Drawing: (1 -- cover -- color) WEST NILE ON THE WEST COAST California braces itself for the virus (2 -- 3) no caption (mosquitos) Illustrations by Jon Gerung/Staff Artist Photo: Health officials created a screening test for West Nile virus that was implemented earlier this month at blood banks nationwide, including at the Red Cross in Van Nuys. Joe Binoya/Special to the Daily News Box: West Nile facts (see text)