The Oregon Department of Agriculture announced last week that a horse from the Richland area, in Baker County, tested positive for West Nile virus (WNV). The horse demonstrated symptoms of incoordination and had stopped eating. The Baker County horse had not been immunized against WNV, but is still alive. In 2004, half of the 32 Oregon horses diagnosed with West Nile Virus died or were euthanized.

According to Oregon State Veterinarian Don Hansen, it is important to note that the virus is passed by mosquitoes, not by horse-to-horse, or horse-to-human contact.

“Mosquitoes, however, can pass the virus to humans,” say Emilio DeBess, public health veterinarian for the Oregon Department of Human Services.”

The virus has also been reported in birds from Jackson and Malheur counties, demonstrating the statewide presence of this disease causing virus. Hansen and DeBess urge the following actions to help prevent the spread of the disease.

Vaccinate horses. For the best protection, horses need to be given two doses: an initial dose and a booster dose 21 days later. If your horse has already been vaccinated with both doses consult your veterinarian about the need for a booster at this time. If your horse has not been vaccinated you are encouraged to vaccinate now.

Control mosquito breeding sites. Help reduce the number of mosquitoes in outdoor areas by draining sources of standing water. In this way, you reduce the number of places mosquitoes can lay their eggs and breed.

Protect yourself. The hours from dusk to dawn are peak mosquito biting times. Consider avoiding outdoor activities during these times or take extra care to use an EPA-registered insect repellent such as those with DEET, picaridin, or oil of lemon eucalyptus. Wear protective clothing.

Observe and report. The virus can infect the central nervous system of horses and cause symptoms of encephalitis. Clinical signs of encephalitis in horses include weakness or paralysis of hind limbs, hyper excitability, ataxia (incoordination), and convulsions.

It is important to note that not all horses with clinical signs of encephalitis have West Nile encephalitis. Call your veterinarian immediately if you witness any of the above symptoms in your horses.