Mid-Atlantic states show WNV resurgence, experts say

New Orleans-While the spread of West Nile Virus (WNV) on the West Coast has been widely documented, a flare-up back in Mid-Atlantic states this year signals that the virus may be very persistent.

Dr. Mike Murray, technical director of equine health for Merial, says, "predicting the future epidemiology of equine WNV cases is mighty risky." Murray made the comments at a Merial-sponsored symposium on WNV that examined the epidemiology, pathology and vaccine research.

Cases of WNV have shown a steady progression to Western states. As the virus marched West in 2002, case numbers dropped in the Midwest and Florida in the aftermath of the initial epidemic. But this year, the Mid-Atlantic states saw a resurgence in new equine cases.

Murray explains, "In the Mid-Atlantic, we saw more cases contrary to conventional wisdom of what would happen." Murray colleted data from state veterinarians' offices on equine WNV cases. In Virginia, Maryland, Pennsylvania and New Jersey there were 201 total reported cases for 2002. The numbers leaped to 1,050 through the late fall of 2003. In Virginia alone, the state documented 48 cases in 2002, and in 2003, it jumped to 228, Murray says. Pennsylvania's numbers increased from 97 cases in 2002 to 522 for 2003.

In a separate presentation, Dr. Keith Roehr, assistant state veterinarian for the Colorado Deptartment of Agriculture, reports that cases of WNV were definitely on the rise out West. For example, Colorado has seen a massive jump in the numbers of human WNVcases. Last year accounted for 2,646 human cases, while there were only 14 reported in 2002. There were 304 WNV equine cases for the state in 2002, and it doubled to 602 last year.

"One factor in the marked increase in human vs. equine cases has to do with equine immunization," he says.

At the symposium Dr. Tricia Salazar reported on a retrospective study conducted at Colorado State University (CSU) to track the epidemic in the state for 2002. Second-year veterinary students helped pull the data together through interviews with owners of affected horses.

While the results are slated for publication in a peer-reviewed journal, one of the interesting survey findings was that animals treated with corticosteroids during the course of their illness were 1.4 times more likely to survive than animals that were not treated. The average time for recovery was 22.3 days.