West Nile virus surges with 27 cases

West Nile virus, spread by mosquitoes, has taken an early hold on parts of California this summer, sickening 27 people statewide compared with only five last year at this time.

Unusually high temperatures throughout the state in March triggered an earlier start to the West Nile virus season than in other years.

Human illnesses have been documented in six counties, led by Kern County with 22, and one each in San Joaquin, Merced, Stanislaus, Glenn and Mendocino counties, state health officials reported Friday. Eighteen of the cases were documented in the last week.

No human illness has been reported south of Kern County this year. But that seems only a matter of time because the virus already has infected animals throughout most of the state.

Dead birds or other animals in 36 of California’s 58 counties, including Los Angeles, Orange, Riverside and San Bernardino counties, have tested positive for West Nile virus, according to the state website tracking the disease, westnile.ca.gov.

The California Department of Public Health warned earlier this month that the rising numbers “could indicate that the mosquito and vector control agencies may have another busy year battling West Nile virus-carrying mosquitoes.”

Dr. Mark Horton, director of the state’s public health department, recently recommended that people take steps to avoid mosquito bites.

“Even though the likelihood of serious illness from West Nile virus is low for most people, all Californians should take every precaution to reduce their risk of exposure,” he said.

One elderly woman in Kern County died from complications of the disease, making her the first death in the state from the virus this year, public health officials announced just over a week ago.

About 80% of people infected with West Nile virus will be asymptomatic, while almost all of the remaining 20% will develop relatively mild symptoms, which can include fever, headache, body aches, swollen lymph glands or a rash on the chest, stomach and back.

Less than 1% will become seriously ill, with those older than 50 particularly vulnerable. Recent data also indicate that people with diabetes or hypertension are at greatest risk.

Severe symptoms can include disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. The neurological effects can be permanent.

In 2006, 292 human infections, including seven deaths, were reported statewide.

California’s first human case this year, a 21-year-old Kern County woman, was reported in mid-June. She tested positive at a local blood bank where she had donated blood, and subsequently she developed a fever and other symptoms.

Public health officials are advising people to apply insect repellent containing either DEET, picaradin or oil of lemon eucalyptus when outdoors, especially in the early morning and early evening. People should also ensure that screen doors and windows are intact and should eliminate sources of standing water, where mosquitoes can breed.

More than twice the number of birds infected with the virus have been detected this year than at this time last year, even though the number of birds tested is similar, according to the state website.

So far, 355 infected birds have been found this year, compared with 150 found through July 20, 2006.

The highest numbers of infected birds have been found in Kern, Stanislaus and Fresno counties.

West Nile virus, first detected in California five years ago, is transmitted to humans and animals through mosquito bites. Mosquitoes become infected when they feed on infected birds. People throughout California can assist with detection by reporting dead birds at westnile.ca.gov or at (877) 968-2473.

marla.cone@latimes.com