West Nile Virus Continues to Take Its Toll in the Horse Industry

Vaccine Available for Use by Horse Owners

According to a recent report from the U.S. Department of Agriculture, as of September 19, there have been 110 cases of clinical West Nile Virus (WNV) infection detected in horses from 11 states since the outbreak began last spring. The states that most recently reported their first equine case(s) in 2001 are: Alabama (Dale County, 2), Massachusetts (Plymouth County, 8), New Jersey (Burlington County, 1), and Virginia (Rockingham County, 1).  Alabama and Virginia never previously had WNV infection detected in horses.

The other 98 cases are in horses from:  Two counties in Connecticut; seventeen counties in Florida; three counties in Georgia; one county in Kentucky; one parish in Louisiana; one county in New York and two counties in Pennsylvania.

At least 23 (21 percent) of the 110 horses died or were euthanized.  The numbers of equine deaths associated with WNV infection by State are: Connecticut, 1; Florida, 15; Georgia, 2; Louisiana, 1; Massachusetts, 1; New Jersey, 1; and New York, 2.

A new report summarizing the extent of the West Nile Virus surveillance data reported to CDC through ArboNET and verified by states and other jurisdictions as of Tuesday, Sept. 25, 2001, states an additional  9 equine cases were reported between Sept. 19 and Sept 25.  The AHC has not received a breakdown of where those cases occurred at time of printing.

Production and use of a new vaccine against West Nile Virus for use in horses received a conditional license from the USDA in July.  Because of limited supply, distribution of the vaccine is on a first-come, first served basis in order to meet the demands of the horse industry in states threatened by the virus.

It is recommended that horses at risk of contracting West Nile Virus be immunized.  Currently, no restrictions on international movement have been placed on horses from the U.S., either because of the WNV outbreak or use of the vaccine.  This, of course, could change and the AHC continues to monitor the situation closely.

Additional information regarding the occurrence of WNV in humans, birds and mosquito pools comes also from the CDC report referred to above as published in ProMed Digest and indicates that during 2001, a total of 20 human cases of WNV encephalitis have been reported in New York (6), Maryland (5), Florida (4), Connecticut (3), Georgia (1), and New Jersey (1); a total of 2521 crows and 952 other birds with WNV infection have been reported from 23 states and the District of Columbia; and a total of 568 WNV-positive mosquito pools have been reported from 12 states (Connecticut, Florida, Georgia, Illinois, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, and Rhode Island).