Extensive rain, flooding, and warm temperatures have created prime conditions for mosquitoes, heightening the risk of the pests transmitting West Nile virus (WNV) and Eastern equine encephalitis (EEE), or "sleeping sickness," to horses. University of Missouri College of Veterinary Medicine (CVM) veterinarians Philip Johnson, BVSc (Hons), MS, Dipl. ACVIM, Dipl. ECEIM, MRCVS, professor of equine medicine and surgery. and Alison LaCarrubba, DVM, Dipl. ABVP, head of the CVM’s equine ambulatory section, say horse owners–both in Missouri and elsewhere–should take preventive measures against mosquitoes and vigilantly watch for signs of WNV and EEE from now through October.

"Since WNV was first reported in Missouri in 2001, increased awareness and the availability of effective vaccines have combined to significantly reduce the incidence of the virus among Missouri horses," said Johnson. "However, horse owners need to be extremely cautious this year because the warm, wet weather and extensive flooding increases the risk of WNV spreading."

West Nile virus can cause equine encephalomyelitis, a potentially fatal inflammation of the brain and spinal cord. There were five diagnosed cases of WNV in Missouri in 2010, according to the USDA Animal and Plant Health Inspection Service. However, this is commonly underreported, Johnson said.

Owners should vaccinate their horses against WNV and EEE and booster the vaccinations annually. They should also remove water from flooded pastures or paddocks, water troughs, ornamental water decorations, gutters, and other sources of standing water. They also can utilize commercially available nontoxic water treatment products that kill mosquito larvae