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Summer Weather Related to Some Disease OutbreaksBy Kentucky Equine Research Staff · July 25, 2012

Potomac horse fever (PHF) has been reported in Indiana, and West Nile virus (WNV) was found in a mosquito in Ohio. This summer’s hot, dry weather may have something to do with the incidence of these diseases.

Veterinarians in Indiana have more commonly seen PHF in late summer and early fall, coinciding with a rise in the number of freshwater snails, caddisflies, and dragonflies that carry the bacteria that spread the disease. This year’s warm weather in early spring may have reset the life cycles of these creatures, bringing an earlier onset of the malady. Horses with PHF may show colic, diarrhea, and dehydration. Treatment with antibiotics and NSAIDs is usually successful, though horses can die from untreated PHF.

WNV is spread by infected mosquitoes that breed in standing water. Dry summer conditions have allowed many streams to turn into a series of shallow pools which are ideal for producing a large crop of mosquitoes. The disease produces neurologic signs such as stumbling, uncoordinated gaits, depression, and muscle twitching, and can be fatal if not treated. Horse owners can use management steps to reduce the chance of horses being infected by keeping vaccinations current, eliminating standing water throughout horse properties, and minimizing the number of lights in or near barns at night.