MARINE CORPS BASE CAMP PENDLETON, Calif. -- Amid a tripling of national West Nile virus cases in one week and the predicted spread of the virus to the West Coast, Navy medical officials are offering advice on how to avoid contracting the mosquito-transmitted virus but aren't taking any sweeping measures just yet.

That's because to date, only one Southern Californian has contracted the virus - and she works at the L.A. Airport.

That was last year. So far this year, no one has come down with the virus, which is rarely fatal or even symptomatic.

So military and other medical officials say California seems devoid of the virus.

For now, military medical officials are simply recommending precautions, although discussions involving Navy entomologists, health officials and base wildlife officials are ongoing as a plan is being devised to respond to the mosquito-delivered virus, wildlife and health officials say.

An Army veterinarian on base recommended changing unchlorinated, standing water every 48 hours, the common breeding cycle for mosquitoes. She also recommended vaccinating horses against the virus.

"There's a very effective vaccine for horses," said Army Capt. Michelle R. Peacock, the officer-in-charge of the West Coast Branch for Veterinary Services here.

No vaccine has been approved for humans.

For now, health officials are offering guidance on protection against the virus.

The first line of defense is to wear long-sleeve shirts or use adequate amounts of insect repellent. The active ingredient in bug spray is DEET (diethyl-m-toluamide) and the repellent should contain at least 30 percent, said Navy Lt. Peter J. Obenauer, the entomologist for 1st Medical Battalion, 1st Force Service Support Group.

Another precaution - spraying uniforms with an insecticide known as Permethrin. The insecticide was used extensively on uniforms worn by Marines and sailors deploying as part of Operation Iraqi Freedom. But widespread spraying of uniforms here for protection against mosquitoes currently has not been recommended, said Lt. Tracy L. Negus, an entomologist at the Navy Environmental and Preventive Medicine Unit No. 5 in San Diego.

A few telltale signs of an emerging health problem here come up negative - among them, changes in bird death rates.

West Nile virus often will manifest itself in increased bird fatality rates if there's a problem. Crows and ravens are especially susceptible to the virus. But so far, those populations seem to be doing fine, according to Vic Yoder, the base game wardens supervisor, whose office is responsible for retrieving dead animals on base.

"There's nothing that we've seen this year to indicate an increase in bird deaths," Yoder said Tuesday.

While California seems virus-free, much of the rest of the nation is being stung by the virus.

During the first week of August, West Nile virus cases tripled in the United States. As of Aug. 7, the number of cases in the United States was at 164, compared with 112 at the same time the previous year, according to the Associated Press.

Last year, 4,156 people caught the virus, and 284 mostly elderly people died, according to the report by AP, citing statistics provided by the Centers for Disease Control in Atlanta. Health officials expect the virus to spread to all corners of the United States this year, the report said.

According to state health officials, seven elderly people have died from the virus this year, four of them were in Colorado, the hardest-hit state, the AP report said.

The virus is being carried across the United States by the Culex species of mosquito, which primarily feeds on birds. The mosquitoes bite humans when they cannot find birds to prey on, said Obenauer.

"Even though mosquitoes that breed in urban areas tend to feed on birds, every now and then, they bite humans and transmit the West Nile Virus," said Obenauer.

Mosquitoes are a threat to humans because they breed in urban areas. Urban areas have all the components to make perfect breeding grounds for mosquito larvae, including sewers and drains, Obenauer said.

Only one in 150 people who contract the virus show symptoms. "Many people might be infected with the West Nile virus, but they don't know it," said Obenauer.

In some cases, patients experience mild flu-like symptoms, including muscle aches and swollen glands, said Obenauer. Disorientation, high fever, neck stiffness, tremors, convulsions, vision loss, coma, numbness and paralysis can also result.

These symptoms can last several weeks and neurological effects may be permanent, according to the CDC Web site, www.cdc.gov.

People who have suppressed immune systems are most likely to contract the virus. Suppressed immune systems primarily exist in elderly people or people with Acquired Immune Deficiency Syndrome.

Individuals with suppressed systems that have been infected with the West Nile Virus may start developing meningitis and encephalitis, which includes dizziness, confusion, coma and sometimes death, said Obenauer.

There's no cure for the virus. The only way to fight the virus is to stay healthy. Healthy immune systems will eventually beat the virus, said Obenauer.

Negus noted that no cases of West Nile virus have been identified this year on the West Coast. If the virus shows up here, proper precautions will be taken, Negus said. Information on prevention will be disseminated and Permethrin will be sprayed on uniforms, she added.

Meantime, she urged base personnel and local residents to report sightings of dead birds.

"Dead birds can be reported to the county, and if they are in the proper condition, they will accept them for testing or may have someone collect them."

Rob Lovich, a base wildlife biologist, echoed Negus' comments. He said the base also is spreading the word about birds as an indicator.

He said crow and raven populations are especially vulnerable.

"They get hammered. They drop out quickly (when West Nile virus hits)," he said.

Upwards of three to four dead birds in one area is an indication that something is wrong, said Obenauer.

To report dead birds, call the California Department of Health Services at 1-877-968-2473 or fill out a form online at www.westnile.ca.gov.

Pfc. Khang T. Tran contributed to this story.