Horse owners urged to guard against mosquito-borne viruses

Mosquitoes like this female Aedes (Ochlerotatus) sp.,
A female Aedes (Ochlerotatus) sp. mosquito,

Horse owners in the US are being urged to inoculate their animals against mosquito-borne virus as summer weather beckons.

The advice comes from the equine specialist with Louisiana State University’s AgCenter, Neely Walker, who said most of the 71 cases reported in the state last year could have been prevented with vaccination.

West Nile Virus and eastern equine encephalomyelitis are prevalent in Louisiana and can cause death in horses. Last year, 63 cases of West Nile virus and eight cases of eastern equine encephalomyelitis were reported across Louisiana.

“The majority of these cases could have been prevented with vaccination,” Walker said.

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

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 by being 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 West Nile virus may have a loss of appetite, depression, fever, weakness or paralysis of the hind limbs, muscle fasciculation or muzzle twitching, impaired vision, poor coordination, head pressing, aimless wandering, convulsions, inability to swallow, circling, hyper-excitability or coma.

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

Animals that become infected with eastern equine encephalomyelitis, or “sleeping sickness”, may show signs of fever, lethargy and loss of appetite. Neurological signs usually develop five days after infection and include impaired vision, circling, head pressing, wandering, difficulty swallowing, hyper-excitability, ataxia, convulsions and death.

The mortality rate for eastern equine encephalomyelitis usually exceeds 90 percent and most deaths occur two to three days after onset of neurologic signs.

Vaccines for both diseases must 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, 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 said vaccines are not always 100 percent effective, and other measures can be taken to reduce the disease risk.

These 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 chemical repellents designed for horses.
  • 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.
  • Cleaning storm drains and gutters in areas where horses are kept.

Reporting: Bruce Schultz

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