Susan Buckley, RN, Director, Public Health
Ira Singh, MPH, Deputy Director
Donald I. Baird, MD, Health Officer

Division of Environmental Health


Date Released: 8/5/2004
Subject: West Nile Virus Confirmed in Humboldt County Raven
Contact: Brian Cox, Director, Environmental Health Division
Phone: (707) 445-6215

A Common Raven from McKinleyville has tested positive for West Nile Virus (WMV), the first indication of the arrival of the virus in Humboldt County. The California Department of Health Services confirmed presence of the virus in eight new California counties this morning. The counties of Alameda, Glenn, Marin, Placer, Solano, Sonoma, and Stanislaus join Humboldt in identifying the initial presence of the virus. There are now a total of 27 California counties where West Nile is present.

The bird was tested as part of the West Nile surveillance efforts being carried out by the Environmental Health Division. West Nile Virus is a mosquito borne disease passed by infected migratory birds. As the virus has migrated across California this summer, positive birds have been identified about four to five weeks before human cases are seen in an area. Some bird species, crows and ravens for example, are very susceptible to the disease and act as sentinels, marking the initial arrival of WNV in an area. Southern California counties identified infected birds in April and May, with human cases seen in June and July. There are currently eighty-five human cases in California, ranging from Anaheim to Fresno.

Humans and horses bitten by infected mosquitoes acquire the disease, but are not capable of passing the virus and are considered dead end hosts. About eighty percent of those bitten by an infected mosquito are protected by their immune response and feel no effects. An estimated twenty- percent of those bitten will acquire West Nile Fever. Symptoms of West Nile Fever can include a fever of over 100 degrees for greater than five days, muscle soreness and a run down, lethargic feeling, and in some cases muscle tremors, nausea, and rash. This condition can last from five to twenty five days. Anyone experiencing these symptoms is encouraged to see their physician or medical care provider. Patients diagnosed with West Nile Fever are treated with supportive care and often remain at home.

According to the Federal Centers for Disease Control, about one percent of those bitten will acquire encephalitis, a swelling of the tissues around the brain, a condition that requires hospitalization. There is currently no vaccine available to protect against WNV, although a modified form of the Yellow Fever vaccine is being tested and may be available in 2008.

The mosquito involved with West Nile transmission is called Culex tarsalis, and is not a major player in the mosquito biology of Humboldt County. Local surveillance over the past several years indicates that less than 10 percent of local mosquitoes are capable of spreading the virus. Most mosquitoes from the salt marshes along the Humboldt Bay and seeps in redwood forests are primarily a nuisance and not involved in disease transmission.
Warm spring and summer temperatures are allowing a large number of mosquitoes to develop, and the disease-carrying mosquito can take advantage of this. It is very important to control breeding sources around the home.
The five gallon white plastic bucket with a few inches of water can produce 200 mosquitoes every two to three weeks. Homeowners are urged to check for sources of standing water that can act as breeding sources and empty them or “Kick the Bucket”.

Personal protection also becomes very important with the arrival of the virus and citizens are urged to “Fight the Bite” with some simple measures. Insure that window screens are tight, avoid activities as much as possible at dusk and dawn when mosquitoes are active, and wear long sleeves and pants as protection if the climate allows. Use of mosquito repellant is encouraged. Most repellants contain DEET, and if used according to label directions, is safe and effective. Other alternative repellant products are also available, allowing the individual a choice of methods that can afford protection to family members. The most important aspect is to use a repellant of choice if in an area where mosquitoes are active.

Humboldt County Environmental Health Division will continue with surveillance and control efforts, including the testing of dead birds, and identifying and controlling disease bearing mosquitoes. Questions about West Nile Virus and mosquitoes may be directed to the Environmental Health Division at (707) 445-6215 or by dialing 1-800-963-9241. You may request information be mailed or visit the local county web site located at . Links are available to the California West Nile web site and the national Centers for Disease Control site which include maps and current case information.


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