The California Department of Public Health is warning residents to take precautions when going outside as the level of West Nile virus activity in the state continues to increase.
"While there have been no human cases of West Nile virus reported so far this year, it is only a matter of time before we see the first case," said Dr. Karen Smith, the CDPH director and state health officer. "As people go outdoors to enjoy the warm weather we've been experiencing, we'd like them to be safe and know how to protect themselves against West Nile virus."
Thirty-one California counties have reported WNV activity so far this year, 10 more than this time last year and above the five-year average of 18. To date, 240 mosquito samples have tested positive for WNV, six more than last year at this time. The virus has been detected in both Stanislaus and Merced counties, with four dead birds testing positive for the virus in Stanislaus.
WNV is influenced by many factors such as climate, the number and types of birds and mosquitoes in an area, and the level of immunity in birds to WNV. It is possible that the drought has contributed to West Nile virus amplification by reducing sources of water for birds and mosquitoes. As birds and mosquitoes seek water, they are coming into closer contact and amplifying the transmission of the virus.
In 2014 there were a record number of deaths from West Nile virus in California, with 31 fatalities, and 561 cases of the West Nile neuroinvasive disease, which is the more serious neurological form of the disease often resulting in encephalitis or meningitis.
Within Stanislaus County there were two fatalities and 38 cases of the neuroinvasive form in 2014, the Stanislaus Health Services Agency reported.
West Nile virus is transmitted to humans and animals through a mosquito bite. Mosquitoes become infected when they feed on infected birds.
In the United States, most people are infected from June through September, and the number of these infections usually peaks in mid-August, according to the Centers for Disease Control. Seasonal outbreaks often occur in local areas that can vary from year to year.
Approximately 1 in 5 people who are infected with West Nile virus will develop symptoms such as fever, headache, body aches, joint pains, vomiting, diarrhea, or rash. Less than 1 percent will develop a serious neurologic illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues). About 10 percent of people who develop neurologic infection due to West Nile virus will die, according to the CDC. People over 50 years of age and those with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and organ transplants, are at greater risk for serious illness. There are no medications to treat or vaccines to prevent West Nile virus infection. People with milder illnesses typically recover on their own, although symptoms may last for several weeks or months. In the neuroinvasive forms, patients can suffer severe and sometimes long-term symptoms.
The California Department of Public Health recommends that individuals prevent exposure to mosquito bites and West Nile virus by practicing the "Three Ds:"
1. DEET - Apply insect repellent containing DEET, picaradin, oil of lemon eucalyptus or IR3535 according to label instructions. Repellents keep the mosquitoes from biting you. DEET can be used safely on infants and children 2 months of age and older.
2. DAWN AND DUSK - Mosquitoes bite in the early morning and evening so it is important to wear proper clothing and repellent if outside during these times. Make sure that your doors and windows have tight-fitting screens to keep out mosquitoes. Repair or replace screens with tears or holes.
3. DRAIN - Mosquitoes lay their eggs on standing water. Eliminate all sources of standing water on your property, including flower pots, old car tires, rain gutters and pet bowls. If you know of a swimming pool that is not being properly maintained, please contact your local mosquito and vector control agency.
Both the Eastside and Turlock Mosquito Abatement districts can treat mosquito habitats using ground and aerial spray equipment. The districts use aircraft in rural locations and ground equipment for more precision spraying in urbanized areas. The districts continue to be concerned with neglected swimming pools. The districts also provide mosquito fish, free of charge, to put in ornamental ponds and other backyard locations.
Reporting and testing of dead birds is an important step in preventing West Nile Virus. A confirmed case of the virus in dead birds or mosquito samples helps to identify areas that need treatment to reduce mosquito activity. To report a dead bird, call the California State hotline at 1-877-WNV-BIRD or report it online at www.westnile.ca.gov. Birds of particular interest are crows, ravens, magpies, jays and raptors (hawk or eagle).
To report mosquito-breeding problem areas, Stanislaus County residents should contact one of the two mosquito abatement districts that serve the county. For Stanislaus County addresses north of the Tuolumne River, residents should call the Eastside Mosquito Abatement District at 522-4098 (www.eastsidemosquito.com) and all others should contact the Turlock Mosquito Abatement District at 634-1234 (turlockmosquito.org).