SOUTH DAKOTA ANIMAL INDUSTRY BOARD
For Release: August 8, 2002
Sam D. Holland, South Dakota State Veterinarian

West Nile detected in additional counties

West Nile Virus continues to spread through the state. Dr. Sam Holland South Dakota State Veterinarian reports 28 cases of West Nile Virus in horses and 11 cases in birds, the horses have been found in the following counties:

     Brookings: 3 horses                 Hanson: 1 horse
     Brown: 3 horses                        Kingsbury: 2 horse
     Butte: 3 horses                          Marshall: 3 horses
     Charles Mix: 3 horses              Minnehaha: 1 horse
     Codington: 1 horse                   Roberts: 2 horses
     Douglas: 1 horse                      Stanley: 1 horse
    Grant: 1 horse                            Walworth: 2 horses
    Gregory: 1 horse

Additionally WNV has been identified in a sampling of migratory birds in an investigation involving a disease outbreak amongst pelicans and cormorants on Bitter Lake in Day County. While the significance of WNV in the bird loss is unclear at this time, the presence of WNV suggests another potential reservoir and precautions against mosquitoes should be enhanced.

Most of the affected horses were not vaccinated for WNV, several had received a single dose, but had not received a booster dose. West Nile Virus vaccine is conditionally licensed and studies show a minimum of 2 doses at 3-4 week intervals are required for protection

Few horses exposed to WNV become infected, those that do can become very ill and medical care can be costly. Horse owners are encouraged to consult their Veterinarian and get their horses vaccinated.

West Nile Virus is not a contagious disease from horse to horse so no quarantine is issued for infected premises or animals. West Nile Virus is carried from birds, which act as the reservoir, by mosquitoes to other animals such as the horse, and other equidae (mules, donkeys). The disease can be confused with Western Equine Encephalitis or sleeping sickness, which has existed in South Dakota in the past. Pets, other farm animals, and wildlife (other than birds) appear to be resistant to the disease.

"We really expected the birds to provide sentinel indicators of the presence of the disease, but the disease was found in horses the same week as in birds. There is a tremendous population of migratory birds traveling through and remaining in South Dakota. This could possibly explain the higher presence of WNV here than in our states immediately to the east. It seems West Nile Virus is now established in the state and we need to resign ourselves to living with the risk, and including WNV vaccination as part of our health program for horses along with sleeping sickness, tetanus, influenza, and other equine diseases" says Dr. Holland. 

For updates on West Nile Disease in horses contact the AIB website at: www.state.sd.us/aib/