Few equine WNV cases reported this year, so far

By KARI KRAMER | East Texas Edition

So far this year, only five horses have been diagnosed with West Nile Virus, compared to over 700 cases at the end of 2003. Still, health officials encourage owners of equine - whether it's a horse or mule (as pictured) - to vaccinate their animals, and to eliminate mosquito's breeding areas. -- Staff photo by Carolyn Rost

July 20, 2004 -- According to numbers from the Texas Department of Health-Zoonosis Control Division, West Nile Virus numbers are low in comparison to last years' trends.

Last year, Texas had 2,759 confirmed cases of the West Nile Virus. To date, in 2004, only 33 positive cases of the virus have surfaced. The first reported human death due to WNV for 2004 was reported July 13 in Orange County. On July 15, reports were released of a Jefferson County man being hospitalized with WNV.

WNV is also a serious threat to equine. In 2003, there were 717 cases of WNV found the Texas equine population. As of July 12 this year, only five equine cases have been reported in five counties: Brazoria, Fort Bend, LaSalle, Leon, and Montgomery counties.

Dr. Fearney Hough, head of Diagnostic Services for the Texas Veterinary Medical Diagnostic Laboratory in College Station, has noticed the decrease in WNV numbers in equine. Hough attributes the decrease in WNV cases to two factors. One he says is vaccinations.

"The numbers are lower than what I anticipated," said Hough. "A large portion of the equine population has been vaccinated."

Hough also accredited the decrease in virus numbers to last year's high exposure levels.

"Potentially some animals may have been exposed and the immunity increases. It's a natural immunity booster."

WNV is a disease carried by mosquitoes that have bitten an infected bird. The birds most commonly found with the disease are blue jays, crows, and hawks. Hough said other species carry the virus, but not usually at concentration levels high enough to kill the bird or transmit the virus to mosquitoes.

Hough said birds carry many viremia (a virus in the blood stream). The WNV comes from birds with a persistent viremia, and also from a WNV epidemic that can follow a mild winter.

"Mosquitoes in the northern part of the state die off in the cold winter. After a mild winter, such as we had this year, those mosquitoes will still be here and continue spreading the disease," said Hough.

Caution against the WNV is also coupled with a concern for several strains of viral encephalitis. "Viral encephalitis is a term that includes diseases caused by a variety of viruses. These diseases are best known for affecting horses and people. The viruses are spread through the bites of mosquitoes," according to TDH's Zoonosis Control Division website.

According to Hunt County veterinarian, Dr. L.P. Gregg, horse owners can protect their animals from the strains of encephalitises, as well as WNV.

"Fort Dodge makes a strait WNV vaccine, and then makes the WNV and encephalitis combination."

The combination shot protects against the Eastern and Western encephalitis viruses and WNV.

Merial is the other manufacturer of a WNV vaccination.

Gregg said an initial shot should be given, followed by a booster of the same four to six weeks later. Depending on the mosquito concentration in an area, follow-ups should be administered every six months or annually.

"You either have to protect from the virus in the case that exposure occurs, or eliminate the possibility of exposure," said Hough.

Hough recommended to decrease exposure chances, keep property free of standing water, use many of the same precautionary measures recommended for humans, and DEET repellents should be used.

Hough and Gregg were both adamant about maintaining a strict vaccination schedule.