September 26, 2001
CALIFORNIA MOSQUITO SURVEILLANCE
for West Nile Virus Carrier!
By William Heasrtstone, Staff Writer

   FRESNO STATE -- California is expanding its surveillance for West Nile virus and other mosquito-borne viruses, State Health Director Diana Bontá, R.N., Dr.P.H., announced today.
     The state already has an extensive monitoring system for St. Louis encephalitis and Western equine encephalomyelitis. Seven people died and 55 became ill from West Nile virus on the east coast last summer after its detection in New York. Three cases have been confirmed in New York so far this year.
     Services (DHS) has collaborated with the University of California and about 50 local mosquito and vector control agencies throughout California to look for St. Louis encephalitis and Western equine encephalomyelitis," she said.
     "When virus activity is detected, the local districts initiate special efforts to control mosquitoes in the area before humans are at high risk. This system has prevented outbreaks of mosquito-borne diseases in California." St. Louis encephalitis has been detected this summer in mosquitoes and sentinel chickens in Riverside and Imperial counties.
     This virus is detected each summer, primarily in Southern California. Western equine encephalomyelitis usually is found every summer in California, mostly in the Central Valley, it has not yet been detected this year.
     In most healthy individuals, infection with St. Louis encephalitis and Western equine encephalomyelitis viruses produces only mild symptoms, such as headache, fever, fatigue or muscle ache.   
     Severe and potentially fatal illness can occur among infants and the elderly. No human cases of St. Louis encephalitis or Western equine encephalomyelitis have been reported in California since 1997.
     Most individuals exposed to West Nile virus experience low-grade fever, slight fatigue, aches and mild headache. A smaller percentage may experience general flu like symptoms, including fever, headache, muscle ache and swollen lymph nodes.
     The elderly and individuals with immunocompromised systems may experience severe headache, neck stiffness, high fever, various central nervous abnormalities and sometimes death. Through the collaborative system, mosquitoes are collected and tested for the presence of the viruses. Approximately 200 flocks of sentinel chickens also are maintained throughout the state to monitor virus activity in mosquitoes that bite them.
     Blood samples are obtained from chickens every two weeks and examined by DHS' Viral and Rickettsial Disease Laboratory in Berkeley for evidence of exposure to St. Louis encephalitis, Western equine encephalomyelitis and now West Nile virus. Chickens are ideal for surveillance because they develop antibodies to mosquito-borne viruses, but do not become ill when exposed to the viruses. The testing process does not harm the chickens.
         The expanded surveillance system is possible through a $90,000 grant from the federal Center for Disease Control and Prevention. The funding will enhance DHS' ability to monitor for the emergence of West Nile virus in California by allowing the testing of dead birds, increased testing of humans with meningitis and encephalitis, and increased testing of horses with encephalitis.
     Bontá urged Californians, particularly residents who live or work near rural wetlands, to take the following precautions against mosquito bites: Avoid activity outside at dawn and dusk when mosquitoes are most active.
     When engaging in outdoor activities, wear long pants, long sleeve shirts and other protective clothing and apply insect repellant according to label instructions. Keep infants indoors during peak mosquito hours.
    If outside, cover cribs, bassinets or playpens with suspended mosquito netting. Identify and eliminate all sources of standing water around property that can support mosquito breeding.
     For more mosquito control ideas or to report unusual mosquito activity, contact your local mosquito and vector control district. Horses also are susceptible to mosquito-borne viruses and should be vaccinated each year.