US horse cases of West Nile virus surge amid late summer mosquito activity

Eight new equine West Nile virus cases have been reported across Indiana, Michigan, California and Utah. Several affected horses were unvaccinated, reinforcing veterinary guidance on vaccination as mosquito activity continues across the US.

West Nile virus is continuing to surface in horses across the US as mosquito activity persists into late summer.
Recent reports from the Equine Disease Communication Center point to fresh cases in Indiana, Michigan, California and Utah, with several affected animals unvaccinated.

Eight new equine infections have been identified. In Indiana, three unvaccinated horses tested positive: a Percheron gelding in Wayne County, a Hackney pony in Lake County that was euthanised, and a Standardbred filly in Adams County that remains alive but showed neurological signs. Michigan reported one case in Missaukee County.

California confirmed an unvaccinated warmblood mare in El Dorado County, which is recovering after developing neurological symptoms. Utah has seen three cases: a Quarter Horse gelding in Utah County that is recovering after hospital care, a Missouri Fox Trotter gelding in Summit County that was euthanised, and a draft-cross mare in Box Elder County that is recovering.

The EDCC says WNV spreads through infected mosquito bites and can cause fever, lethargy, muscle fasciculations, ataxia and other neurological signs. There is no cure, but supportive treatment can help some horses recover. Veterinary guidance from state authorities underlines the value of vaccination, with boosters advised annually and, in some regions, twice a year where mosquito seasons are prolonged.

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