Horse Owners Advised to Guard against Mosquitoes

The Louisiana State University (LSU) AgCenter equine specialist is advising horse owners to protect their animals against diseases spread by mosquitoes that are becoming more active with the warmer weather.

Two mosquito-borne diseases—West Nile virus (WNV) and eastern equine encephalomyelitis (EEE)—are prevalent in Louisiana and can cause death in horses. Last year, 63 cases of West Nile and eight cases of EEE were reported in horses across Louisiana.

“The majority of these cases could have been prevented with vaccination,” said Neely Walker, MS, PhD, assistant professor and Extension equine specialist at the LSU AgCenter.

This year’s first case of West Nile virus in Louisiana was detected in a bird found in Lafayette earlier this month, she said.

Both diseases can cause infection of the brain and spinal cord or their protective covering.

“While each disease is caused by a specific virus, they are both transmitted to horses (when the horse is) bitten by an infected mosquito,” Walker said. Horses are considered to be a dead-end host for both diseases, meaning that the virus is not directly contagious from horse to horse.

Horses infected with WNV can exhibit a loss of appetite, depression, fever, weakness or paralysis of the hind limbs, muscle fasciculation or muzzle twitching, impaired vision, ataxia (incoordination), head pressing, aimless wandering, convulsions, inability to swallow, circling, hyperexcitability, or coma.

“Currently there is no specific treatment for West Nile virus, and this disease has a 30% mortality rate,” Walker said.

Horses that become infected with EEE or “sleeping sickness” can show signs of fever, lethargy, and loss of appetite. Neurologic signs usually develop five days after infection and include impaired vision, circling, head pressing, wandering, difficulty swallowing, hyperexcitability, ataxia, convulsions, and death.

The mortality rate for EEE usually exceeds 90% and most deaths occur two to three days after onset of neurologic signs.

Vaccines for both diseases should be administered according to the label and veterinary recommendations, and a yearly booster is required, Walker said. Horses that are stressed, travel frequently due to show schedules, or live in warm and humid climates should be vaccinated twice a year.

Vaccination should be done before peak mosquito breeding season and a multi-faceted management approach ensures reduced exposure.

But Walker cautions that vaccines are not 100% effective, and other measures can be taken to reduce the disease risk.

The recommendations include:

  • Keeping horses indoors during peak periods of mosquito activity at dusk and dawn, if possible;
  • Reducing the use of artificial light when mosquitoes are active;
  • Using fans to help keep mosquitoes off horses while they are stabled;
  • Using topical repellents designed for use on horses and/or protective fly masks, sheets, and boots;
  • Eliminating areas of standing water in such locations as discarded tires, manure storage areas, drainage areas, wheel barrows, pots, and shallow ponds;
  • Cleaning livestock water troughs weekly or adding a supply of mosquito fish, which will feed on mosquito larvae; and
  • Cleaning storm drains and gutters in areas where horses are kept.