The West Nile Virus is closely related to St. Saint Louis Encephalitis Virus which has been historically found in the United States including Orange County. West Nile Virus has been known from parts of Asia, Eastern Europe, Africa, and The Middle East for many years. The virus was first detected in the United States in 1999 in New York City. West Nile Virus is transmitted by infective mosquitoes and can infect humans, birds, horses, and many other animals.
A mosquito acquires the virus by biting an infected bird. The virus then multiplies in the mosquito. It is transmitted to a new host in the mosquito's saliva when it feeds again on a person or an animal. Humans and horses are "accidental hosts" for West Nile Virus, and cannot pass on the infection to another mosquito. There are records of transmission through blood transfusion and organ transplants but human-to-human transmission is extremely rare.
Since 1999, West Nile Virus has spread remarkably fast; by late summer of 2003, Imperial, Riverside, Los Angeles and Orange Counties were reporting infected birds and mosquitoes. By the end of 2003, 46 states had reported West Nile Virus activity. In March of 2004, evidence of recent transmission was found in birds from Orange County.
Many Animals can be bitten by an infected mosquito, but they won't all become ill; some may show no symptoms. West Nile Virus most often affects birds, but occasionally causes disease in other animals as well.
Wild birds are the reservoirs for West Nile Virus; while most infected birds will not become ill, for some others, the virus can cause serious illness and death. Birds of prey, and crows, ravens, jays, and magpies are seriously threatened by West Nile Virus. The virus does not appear to cause extensive illness in dogs or cats.
Horses are extremely susceptible to West Nile Virus. Clinical signs of disease consist of central nervous system abnormalities similar to those caused by infection with Eastern Equine Encephalitis and Western Equine Encephalitis. West Nile vaccines are now available for horses.
Most people who are infected with West Nile Virus experience no symptoms. Symptoms of mild illness may include one or more of the following: unusual fatigue, malaise, fever, headache, and body aches, a skin rash on the trunk of the body, and / or swollen lymph nodes. These symptoms generally last a few days. In severe cases, the disease may progress to encephalitis. Symptoms may include high fever, headache, neck stiffness, disorientation, coma, tremors, and paralysis. Symptoms may last several weeks, and neurological effects may be permanent. It is estimated that 1 in 150 people who are infected with West Nile Virus will require hospitalization. Those most at risk are the elderly and those who have weakened immune systems.
The time between the mosquito bite and the onset of the illness, known as the incubation period, ranges from 3 to 15 days in humans.
The Orange County Vector Control District (OCVCD) routinely surveys for mosquito-bourne diseases such as West Nile Virus, and other viruses. OCVCD's wild bird surveillance program is an excellent early warning system which allowed the District to detect evidence of virus activity before there were any human cases. Dozens of finches and sparrows are bled every two weeks and released. Their blood is tested for antibodies to these viruses. Adult mosquitoes are routinely trapped, counted, and tested for these viruses.
OCVCD's Staff controls mosquito breeding on acres of public and private land throughout the County. The District works closely with the California Department of Health Services, The University of California, Davis, Mosquito and Vector Control Association of California and The Orange County Health Care Agency.
To report a West Nile Virus Medical Emergency, please call 911
For non-emergency medical questions regarding West Nile Virus, please contact your Primary Care Physician.
For West Nile Virus general information, visit: cdc.gov/ncidod/dvbid/westnile/index.htm or the California Department of Health Services at westnile.ca.gov
For mosquito problems or general questions, call the Orange County Vector Control District at 714-971-2421, 949-654-2421, or visit ocvcd.org
To report dead birds, call the Orange County Vector Control District at 714-971-2421 or 949-654-2421, ext. 117.
To report West Nile Virus in horses, please contact your local veterinarian and the CDFA Animal Health Branch at 916-654-1447 or visit cdfa.ca.gov/ahfss/ah/wnv_info.htm
For more information, contact the Orange County Vector Control District, at (714) 971-2421 or visit ocvcd.org.
