West Nile virus (WNV) has topped headlines in the Northeast for the better part of 2000, and now has sickened at least 15 horses in the states of Connecticut, New York, New Jersey, Massachusetts, and Rhode Island. As the magazine went to press, only five of those horses were recovering; the others died or were euthanized. Officials are familiarizing themselves with WNV in many ways as they learn more about the epidemiology of the deadly disease. Information gathering includes a written and serological survey of the stables where positive horses have been found.

In the meantime, horse owners in the Northeast are waiting for the first frost to kill off the mosquitoes that carry the virus. But officials feel the virus is not going to spread much farther before the winter.

“I don’t expect to see equine cases in Maryland and Pennsylvania, but I can’t rule it out,” said Randall Crom, DVM, staff veterinarian for the United States Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS), and Coordinator for West Nile Virus Issues. (WNV has been found in dead birds in Maryland and Pennsylvania.) “I think the peak period for equine exposure has passed. That’s not to say there couldn’t be some cases of West Nile in horses that will have onset later than today’s date. But in looking at what happened last year, we only had two horses, if you calculate back from their date of onset, that would have had exposure to the mosquitoes after the first of October.”

Last year was the first time WNV emerged in the Western Hemisphere; it appeared in birds, horses, and humans. Twenty-five horses in New York tested positive for WNV in 1999, and nine of those horses died or were euthanized. This year, the first positive equine case again was in New York. Since then, positives have been found in the five states listed above, but all clinical cases have been at separate farms, except three cases in Orange County, NY