By Kim J. Harmon

Summer may be filled with schooling shows, carriage rallies and trail rides, but to enjoy it all horse owners must continue to be vigilant when it comes to West Nile Virus.

Since June 17, almost three dozen birds have been tested for WNV and of the 19 crows tested, five tested positive. While all mosquitoes (nearly 7,000 in 91 sites across the state) that have been tested have thus far tested negative for WNV, the Department of Environmental Protection is, of course, issuing its usual spate of warnings for communities across the state.

“This finding is a reminder that West Nile virus has not gone away and that we must continue to work together to reduce the potential for serious illness,” said David K. Leff, DEP deputy commission. “Help protect yourself by reducing mosquito breeding sites: clean up standing water and leaf debris around your yard where mosquitoes may breed.”

The first three weeks of mosquito trapping and testing have shown the number of mosquitoes this year are below the five-year average and below last year’s numbers (175 per trap is the five-year average while 120 per trap is the average this year).

Some 84 mosquitoes were trapped on Key Rock Road in Newtown and all have tested negative for WNV.

“In June, the risk of West Nile virus infection to the public is low,” said Joxel Garcia, M.D., Department of Public Health commissioner. “However, it is always a good idea to avoid mosquito bites, especially in areas where West Nile virus has been identified.”

WNV is a vector-borne virus (meaning it is transmitted from species to species) that was first discovered in the western hemisphere back in 1999. In general, mosquitoes most often circulate the virus among wild birds.

But humans and horses do serve as incidental hosts and can contract WNV.

Incidental hosts are infected animals that do not pass the virus on to vectors or other animals.

According to the DEP, the only vectors found to be associated with outbreaks of WNV in its first two years in the northeast United States were mosquitoes. At least 14 species of mosquitoes tested positive for WNV, but no evidence has been found to suggest that any invertebrate vectors other than mosquitoes were involved in WNV transmission in either year.

Horses – more than any other domestic animal – are at risk for WNV. According to the DEP, many horses infected with WNV do not develop any illness, but of the 85 that did become ill in the 1999 or 2000 outbreak, 32 of those (38 percent) died or had to be destroyed.

Other livestock and poultry do not commonly show illness if infected with WNV.

Given that mosquitoes are associated with WNV transmission, the key to preventing or controlling future outbreaks of WNV among horses is to control mosquito populations and to prevent horses from being exposed to any adult mosquitoes that may be present.

Based on DEP information, there are various ways to do that:

+ Screened housing – Housing animals in structures with well-maintained insect screening can be useful to reduce exposure to adult mosquitoes. But remember – use of such mosquito-resistant structures may actually lead to mosquito exposure unless precautions are first taken to eliminate mosquitoes from inside the structure. Use of fans may also reduce the potential ability of mosquitoes to feed on horses.

+ Insect repellents – Use of insect repellents may be of some value in decreasing exposure of horses to adult mosquitoes. Due to practical limitations in the coverage area that may be achieved on any given horse with a particular product formulation, and due to limited duration of effectiveness of some formulations under certain conditions (e.g., perspiration), repellents should not be solely relied upon to prevent mosquito exposure.

+ Outdoor exposure – Although some species of mosquitoes feed at dusk or dawn, others are daytime feeders or feed at any time of the day or night. As it is not yet clear which mosquitoes are responsible for the transmission of WNV to horses and other mammalian species, making recommendations as to when certain animals should avoid outdoor exposure may not be particularly useful at this time. A recent study suggests that keeping horses in stalls at night may be helpful in reducing their risk of infection.

+ Vaccination – On August 1, 2001, a conditional license was issued by the USDA-APHIS Center for Veterinary Biologics for an equine WNV vaccine. The vaccine is a killed virus product that initially has a one-year license. Conditional licensing means that the product has been shown to be safe, pure, and have a reasonable expectation of efficacy in preventing illness caused by WNV.

Resources

For further information, visit the Department of Environmental Protection website at http://www.dep.state.ct.us or call the 24-hour (toll-free in Connecticut) recorded mosquito information line (866) WNV-LINE (1-866-968-5463) or (860) 424-4184. Also, the Centers for Disease Control and Prevention website can be located at http://www.cdc.gov.

Or contact:

Newtown Health District

4 Fairfield Circle South

Newtown, CT  06470-2104

Phone: 270-4291

Fax: 270-1528

Email: newtownhd@earthlink.net