West Nile Threat Level Is Raised

Health officials believe that California is about to have its first significant brush with the West Nile virus.

West Nile disease, which has killed hundreds of people in the United States since it was detected in 1999, has up to now largely bypassed California. But officials say they expect more human cases this year based on how the virus has spread among birds and insects.

The virus is transmitted through the bite of mosquitoes, which infect humans and other animals. The mosquitoes become infected when they feed on infected birds.

West Nile has killed nearly 300 birds and infected one person in California this year.

While the number might not seem particularly large, health experts said it fits a troubling pattern.

The locations of infected birds has shifted from rural areas into densely populated cities such as Downey, Pico Rivera and South Gate.

To date this year, at least 120 West Nile-infected birds have been found in Los Angeles County, compared with less than a dozen in all of 2003.

Health experts have been predicting that California would be hard hit as the virus marches across the Western states.

“Our scientists did determine last year that California would be the next hit, based on the migration,” said Llelwyn Grant, a spokesman for the federal Centers for Disease Control and Prevention.

Since 1999, Grant said, “We saw activities mostly on the Northeast coast, then expanding along the Southeast coast, and through the years have seen this progress westward.”

State health officials announced Tuesday the first human case of West Nile this year. Officials said the infection was discovered in May when a San Bernardino County woman sought treatment for her flu-like symptoms. She has recovered.

Officials were alarmed by how early the case appeared. West Nile cases typically develop in August and September.

California tallied three cases in 2003. All of the victims survived.

Most health officials expect many more infections this year as the virus becomes more prevalent in urban areas, as has been the pattern in other states. The pattern elsewhere has been for the virus to gain a foothold one year and then hit hard the second year.

“There’s the second-year phenomenon, which we in Colorado firmly believe in,” said Dr. Ned Calonge, chief medical officer for the Colorado Department of Public Health and Environment.

Colorado saw 14 human cases of West Nile in 2002 and no deaths. By the end of the 2003, there were almost 3,000 infections and 63 deaths.

Birds -- usually crows, blue jays and ravens -- are hosts for West Nile. And officials said they are concerned because about 70% to 80% of dead birds found by officials in Southern California this year have tested positive for the virus.

Vicki Kramer, chief of the vector-borne disease section of the state Department of Health Services, called the percentage alarming.

“That’s a relatively high percentage of birds to have West Nile as the cause of mortality, so that’s of concern, especially since it’s still early on in the season,” Kramer said.

Experts point to another factor likely to help spread the virus: an early warm spell followed by spring rain, a climate that attracts mosquitoes.

“Based on the activities that we’ve seen, all indications seem to suggest that California will be hit,” Grant, of the CDC, said.

California has been preparing for West Nile since 2000, said Kelly Middleton, spokeswoman for the San Gabriel Valley Mosquito and Vector Control District.

Local mosquito and vector control districts have increased mosquito control and surveillance, alerted doctors and other health experts about how to recognize West Nile patients, and promoted awareness of the virus in schools and communities, officials said.

Once mosquitoes have reached heavily populated areas, there is little the government can do to prevent the virus’ spread. Making people aware of the symptoms and getting medical treatment early is key, officials said.

The majority of people who are infected show no symptoms. The elderly and those people with weakened immune systems are the most susceptible to sickness.

About 20% of those infected experience nausea, body aches, fever and a rash. If those symptoms go untreated, the virus could progress to encephalitis, swelling of the brain that can cause permanent damage. About one in 150 people with West Nile get encephalitis, authorities said.

By taking precautions, such as avoiding mosquito bites by covering up in loose-fitting clothes and ridding homes of standing water, people can prevent illness, Middleton said.

“It’s not something to panic over,” she said.

“Avoid mosquito bites and we may go a long way in preventing an epidemic.”

The most prevalent mosquito in Southern California, the southern house mosquito, is one of two known carriers of the virus. It is a close relative of the species of mosquito that carried West Nile throughout much of Colorado last year.

The first known cases of the disease in the United States were in the New York area in 1999 and seven people died from it that year.

By 2002, the virus had spread from the East Coast to the Great Plains, the CDC said.

Colorado reported the most human cases to the CDC last year, with about 3,000, followed by Nebraska, which had nearly 2,000 human cases.

There is no cure and no human vaccine, but two vaccines are available for horses. Veterinarians have encouraged horse owners to vaccinate their animals, which have an almost 40% mortality rate if they become ill.

This year’s first human case was reported in New Mexico, and six people have been infected in Arizona, Grant said. None has died.