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District Disease Testing of Mosquitoes

Our laboratory simultaneously tests for three encephalitis diseases carried by Culex mosquitoes: West Nile Virus (WNV), Saint Louis Encephalitis (SLEV) and Western Equine Encephalitis (WEEV).

Saint Louis Encephalitis Virus had not been seen in California for over 10 years until it was detected in southern California in 2015 at the same time there was an outbreak of the disease in Arizona. SLEV is similar to West Nile Virus (WNV) in that it attacks the nervous system. Initial symptoms of those who become ill include fever, headache, nausea, vomiting, and tiredness. Long-term disability or death can occur in rare cases. There is no vaccine or cure for SLEV so rapid detection and control of mosquitoes are the best methods to keep the virus from finding its way into people.

Western Equine Encephalitis virus, like West Nile Virus and Saint Louis Encephalitis Virus, attacks the nervous system. The disease is very dangerous for horses with a case fatality rate of 20-30%. Death can occur in just a few days and horses that survive may be permanently damaged. Symptoms in humans include fever, aches and pains but may progress to encephalitis with headache, irritability, vomiting, diarrhea, convulsions, and coma. There is no cure for Western Equine Encephalitis and no treatment except for supportive therapy.

There is good news though! While these diseases are dangerous, most people fight off the infection easily and never know they were infected. All the same, it’s important we control the carrier of these diseases, Culex mosquitoes, to prevent those who are not able to fight off the infection from becoming dangerously ill. There is a vaccine for horses so make sure you talk to your veterinarian about keeping your horse’s vaccinations for WNV and WEEV up to date.

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