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

Division of Environmental Health


Date Released: 8/25/2003
Subject: West Nile Virus and Humboldt County Mosquitoes
Contact: Brian Cox, Director
Phone: (707) 445-6215

West Nile Virus and Humboldt County Mosquitoes

West Nile Virus (WNV), the mosquito borne disease making national headlines this summer, was detected this week in the Imperial Valley in southern California. Local health and mosquito control agencies throughout California monitor for West Nile Virus and other mosquito borne diseases. Humboldt County Department of Health and Human Services is taking a number of steps to protect local residents from mosquito borne diseases, including:

1. Conducting mosquito surveillance, looking for a specific mosquito that is the primary carrier of WNV.
This mosquito, called Culex, does not ordinarily play a predominant role in the ecology of Humboldt County. Surveillance will insure that we detect any change from our more normal populations of mosquitoes.

2. Birds that may have died of suspicious causes are being tested. Some bird species are very susceptible and act as sentinel species. When you find a dead crow or raven (Corvid) or a hawk or an owl (Raptor) call
1-877-WNV-BIRD. If the state decides the bird is in good condition for virus isolation testing, then the County Division of Environmental Health will pick up the bird and ship it overnight express to UC Davis.

3. Local veterinarians must report horses that may have acquired WNV. Areas near horse pasture or paddocks are reviewed for mosquito populations. An equine vaccine is available, so check with your veterinarian about vaccinating your horse against WNV.

4. Physicians are required to report human WNV cases. Human case reporting is a critical component of tracking the movement of WNV through the state. A patient interview is conducted to determine whether the virus may have been acquired locally or during out-of-county travel. On average, only one of 150 people who are infected with WNV will require hospitalization. People infected with WNV cannot spread it to other people.

5. Public education and outreach is being conducted about the risk of the virus locally and steps that can be
taken to reduce the risk of exposure. Ask if your school, non-profit organization, civic club or group would like to have County Division of Environmental Health give a presentation on WNV.

West Nile Virus and Humboldt County Mosquitoes
August 25, 2003
Page 2

Here are some practical steps you can take to reduce your family’s risk of exposure:

1. Reduce breeding sources around the home and neighborhood. We encourage residents to Kick the Bucket, that is, remove “standing water” that acts as a breeding source for mosquitoes. These sources may include:

· Neglected wading pools, hot tubs, birdbaths, & fishponds.
· Boats that are left uncovered and have water in the bottom.
· Tires not stored under cover that have collected water.
· Leaf clogged rain gutters and rain barrels.
· Buckets, flower pots, or any object that holds water

Change water in horse troughs and other containers once a week. Practice balanced pond ecology using frogs, minnows, ornamental koi, or goldfish that devour mosquito larvae. Encourage habitat for swallows, dragonflies, and bats that eat adult mosquitoes.

2. You should also Fight the Bite. Limit activities at dawn and dusk when biting mosquitoes are most likely to be active. Activities in wildlife wetland areas like Hookton Slough National Wildlife Refuge, Arcata Marsh, Fern Canyon, and Mad River Bottoms will encounter many more mosquitoes than elsewhere. Wear long clothes that protect arms and legs. Use mosquito repellants containing DEET (according to label directions) to insure protection when out-of-doors at times when mosquitoes are biting.

3. Advise the Division of Environmental Health when you detect a large concentration of mosquitoes, or see
a condition that may act as breeding sources such as a tire pile or neglected swimming pool. Participate in the dead bird reporting program (1-877-WNV-BIRD).

For additional information about local mosquito monitoring, contact the Humboldt County Division of Environmental Health at (707) 445-6215, toll free at (800) 963-9241., or via e-mail at
The California State West Nile Virus web site, found at, also contains very up-to-date information on statewide efforts at monitoring and control.


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