West Nile Virus poses danger

by Bill Boender

An informational meeting to discuss West Nile Virus was held at the Pinedale Fire Hall meeting room Wednesday, April 16. Terry Creekmore, vector-borne disease coordinator for the Wyoming Department of Health, presented a comprehensive history of the disease as it has spread through the world and into the United States.

The first cases appeared in this country in New York in May of 1999, killing many birds and infecting 99 people, eight of whom died. By 2002, 4,161 people were infected with 277 deaths. Spread has been rapid with five states involved in 2000, 20 states in 2001 and 44 states by 2002. Nebraska had 174 human cases with eight fatalities, while only two cases with no fatalities were identified in Wyoming.

The virus is spread by mosquitoes which feed on birds. Infected birds then pass the virus to more mosquitoes. Crows, jays and related birds are the principal carriers, although 162 bird species have been killed by the virus. In mammals, horses are the most susceptible to the virus. Some 700 horses were infected in 2001, with that number growing to more than 15,000 in 2002. Fatalities in horses range from 24 percent to 39 percent across the country.

Symptoms of the disease are similar to flu. Dr. Tom Johnston, Sublette County Health Officer, feels that the true number of cases far exceeds the reported numbers as many go undiagnosed or untreated. A small but significant number of those cases develop into encephalitis, resulting in death or permanent injury. There is no cure or vaccine available for humans at this point, but vaccines should be developed in about two years.

For horses, an effective vaccine is available but requires two injections several weeks apart and is not effective until two weeks after the second injection. Those who wish to protect horses need to begin the treatment quickly.

One Wyoming mosquito, culex tarsalis, has been identified as a vector for the disease. This mosquito emerges in April or early May and a number will begin spreading the disease then. Many more will contribute to the problem in August and early September when their numbers peak. Less than 1 percent of mosquitoes are expected to carry the virus.

The best course to avoid infection in people is to use DEET repellant, cover bare skin and avoid exposure during peak periods of feeding in early mornings and evenings. Eliminating water sources where mosquitoes breed and spraying to reduce numbers are also effective.

Creekmore will gather dead birds and would like to see any freshly dead crows, jays or magpies found by the public. He can be contacted at 307-742-6638 ext. 105 or by email at tcreek@state.wy.us.

Following the presentation, a panel discussion was held. Panel members were Creekmore, Johnston and Les Burrough, former Sublette County Weed and Pest supervisor. Discussion centered around effective methods of mosquito control and responsibility for implementation. Control can take the form of aerial spraying of malathion or using larvicide.

While malathion is effective and inexpensive, it is also indiscriminate and kills many other insects and birds where it is applied. Bacterial larvicide is specific but is expensive and requires manpower and timing to be effective.

Existing mosquito control boards in the county do not have the resources for countywide control nor the expertise to handle the disease control aspects of this virus. Panel members felt that the county should look into setting up a program to address the situation.

Audience comments included suggestions that the money planned for PDR use would be much better spent on West Nile Virus control.