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| 9/19/2007 12:01:00 AM | Email this article • Print this article
Comment on this article | Letter: Active mosquito trapping programs finds no West Nile here
By Russell Lewis
Friends of the Willapa National Wildlife Refuge
Mosquito trapping for the presence of West Nile virus is nearing completion of its fourth season in Pacific County. Good news so far. The virus has not been detected in Pacific County since trapping began in 2003.
Mosquitos flourish in our general area particularly between the months of May through August. Mosquitos are the only known vector for transmitting this disease. It causes illness in birds, horses and humans.
Recently a deceased crow found in Gearhart, Ore., tested positive for West Nile virus. It becomes especially evident that continued trapping and testing in Pacific County is of utmost importance in alerting our residents at the earliest opportunity anywhere in our county.
It appears that West Nile virus is slowly advancing from points located south and east of us, but it still remains anyone's guess if or when it becomes a reality. If you find a dead crow, jay, raven or magpie, please report it by looking in the phonebook under County Government-Health. These suspected birds must be complete specimens and not have any signs of obvious physical injury.
Goals of mosquito-based surveillance are based on the following criteria:
• Use data on mosquito populations and virus infection rates to assess the threat of human disease.
• Identify geographic areas of high risk.
• Assess the need for a timing of interventions.
• Identify larval habitats for targeted control.
• Monitor the effectiveness of this type of surveillance and improve prevention and control measures.
• Develop a better understanding of transmission cycles and potential vector species.
There are approximately 2,500 different species of mosquitos existing worldwide, of which 150 are found in the United States. Mosquitos can carry diseases such as the malaria parasite and West Nile virus. Any mosquito species determined to carry such diseases are classified as a vector species.
There are 58 known mosquito vector species in the U.S. that are identified as potential carriers of West Nile virus, while only 19 out of these 58 have been identified in Washington state alone. This does not mean West Nile virus is present at this time or that all of Washington's 19 known mosquito vector species are found in Pacific County. However, there could be some vector mosquito species present that are capable of transmitting the virus.
To date the virus has not yet been determined to be present in any of our identified mosquito species known to reside in our area.
Traps are operated every two weeks at different locations on both sides of Willapa Bay under the management of the Willapa National Wildlife Refuge for Washington Department of Health, Office of Environmental Health & Safety, and West Nile Project. The trap consists of a dry ice filled canister with a net trap attached to the underside of the canister. It is attached to a tree limb about six feet above the ground and kept in operation overnight. There is a small electric fan located between the canister and net trap that blows carbon dioxide downward into the net trap from the canisters dissipating dry ice. The carbon dioxide filters throughout the net trap.
Mosquitos are attracted by carbon dioxide and enter the net trap. It is a one-way trip. The trap spends about 12 hours overnight collecting mosquitos. They are then collected, freeze killed and eventually sent off for species identification and testing for the presence of the virus.
One such site is located near Leadbetter Point where mosquitos proliferate during the month of June. Early in the morning this past June 8 there were 1,373 trapped mosquitos humming away in a cylindrical trap about the size of a large can of beans hanging from a limb of a red alder located deep in the woods. Prime habitat for mosquito sampling. It also takes time and patience to carefully tally the numbers. Noteworthy is the fact that protective clothing really is needed when visiting this location as most of these bloodthirsty insects are of the genus Culex who become very aggressive in the presence of humans and pack a small wallop when they bite.
For more information on West Nile virus contact The Department of Health West Nile Virus Web site (http://www.dohwa.gov/WNV) and toll free information line (1-866-78VIRUS) which will have the latest information on bird, horse and human cases in the state. Information on mosquito biology can be found on website (http://www.mosquito.org).
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