Reported EEE cases up, WNV sharply down so far in 2009

Reported EEE cases up, WNV sharply down so far in 2009

Oct 01, 2009

Washington — Reported cases of Eastern equine encephalitis (EEE) during the first eight months of 2009 already have surpassed last year's total in the United States, while West Nile virus (WNV) cases are sharply down from 2008, according to the USDA's Animal and Plant Health Inspection Service (APHIS).

At press time, the latest update posted by APHIS showed 203 total cases of EEE and 75 cases of WNV through Sept. 9. During all of 2008, there were 185 EEE cases and 178 WNV cases.

Both mosquito-borne diseases are preventable by vaccination, but there is concern among equine veterinarians that the down economy may have led some horse owners to neglect vaccinations or under-vaccinate their horses.

The reported cases of both diseases have occurred in 24 states.

Most EEE cases so far this year are in Florida, which reported 67 as of Sept. 9, most of them in the state's north-central and northeast coastal counties. Georgia is second with 36 cases and Mississippi third with 31.

Most WNV cases in recent years have been in western states, reflecting the vector's steady movement from east to west. Washington reported 23 WNV cases by Sept. 2, followed by Montana with eight, Colorado with seven, Idaho with five and California with four cases. No cases of the Western variety of equine encephalitis are reported so far this year.

The American Association of Equine Practitioners (AAEP) issued an updated version of its "Guidelines for the Vaccination of Horses" in 2008. The guidelines were developed by the AAEP's 15-member Infectious Disease Committee, chaired by Mary Scollay, DVM, Kentucky's equine medical director, and comprised of veterinary researchers, vaccine manufacturers and private practitioners. The guidelines are available online at

Eastern and Western equine encephalitis and WNV are among what the American Veterinary Medical Association defines as core vaccines, along with those for rabies and tetanus.

The AAEP says its guidelines are intended as a reference for veterinarians and that, based on the committee's judgment, the recommendations may differ from those provided by manufacturers. "However, it is incumbent on each individual practitioner to reach a decision on vaccine usage based on the circumstances of each unique situation and his or her professional experience," the AAEP says in a preface statement.

Suggested vaccination schedules vary widely by region and other factors, including a horse's age, vaccination history and travels to areas where it might be exposed to different disease risks.

To see the latest APHIS updates on EEE and WNV, visit