Mid-Summer Score: West Nile Virus 16, Eastern Equine Encephalitis 52 as New Cases Added in New York and Massachusetts


As the summer progresses, so does the toll of mosquito-borne diseases, and some new states are being added to the list of those where horses are affected by disease.

In upstate New York’s rural Oneida County, West Nile Virus (WNV) was confirmed on serologic samples from a yearling this week. According to the local ABC News affiliate, WSYR-TV, the horse is located in the town of Vernon, home of a harness track that was hampered by an Equine Herpes Virus outbreak this spring.


A New York Department of Agriculture press release from state veterinarian Courtney L. McCracken, DVM, states that the yearling had no recent travel or vaccination history. On the morning of July 26th, the owner noticed that the yearling was lame in the left hind limb. By the afternoon, the horse was down and was paralyzed in the hind limbs by the time the veterinarian arrived.

The yearling had a temperature of 103.5 but was BAR (bright, alert, responsive) and eating and drinking.

Upon initial exam, the veterinarian took samples to test for EHV-1 and commenced supportive treatment. The following day, EHV-1 samples tested negative at which time arboviral testing commenced at the New York State Veterinary Diagnostic Lab at Cornell University. The IgM Capture ELISA test for West Nile Virus was positive.

Fortunately, on July 27th, the owner reported improvement in the yearling. As of August 8th, the yearling is still alive, and is now standing with some residual ataxia (lack of control) in the hind legs.

There are other horses on the premises but none are showing signs of disease.

Not far away, two horses in the western Massachusetts community of Belchertown were fighting the much more deadly mosquito-borne disease of Eastern Equine Encephalitis (EEE). This is Belchertown’s second EEE-infected horse this year; the town was also affected by EEE in 2012.

On July 26, the Idaho State Department of Agriculture (ISDA) reported that two horses, one near Parma, Idaho, and one near Meridian, Idaho, tested positive for West Nile virus (WNV).

The ISDA recommends taking precautions to protect equines (horses, mules, burros and zebras) and small camelids (llamas, alpacas, vicunas, guanacos) against WNV by using fans and repellents to keep mosquitos away and by keeping livestock up to date on their WNV vaccinations.

The most common sign of WNV in horses is a fever and weakness, usually in the?hindquarters; sometimes seen as a widened stance, stumbling, leaning to one side and toe dragging. Depression and other mental conditions such as fearfulness, lip-smacking, chewing movements and fine muscle tremors may be noticed. In extreme cases of WNV infection, paralysis and inability to stand may follow.

On the southern tier of states, a two-year-old horse in the Livingston Parish town of Maurepas, Louisiana was euthanized after reportedly testing positive for both West Nile virus and Eastern equine encephalitis earlier in July.

North Carolina horses were hit earlier in the summer, when six horses died after contracting Eastern Equine Encephalitis from infected mosquitoes. One horse in that state is currently reported to be recovering, according to the North Carolina Department of Agriculture. All of the reported cases have been in the southeastern part of the state – one each in Pender and Brunswick counties and five in Cumberland County.

North Carolina officials remind horse owners that symptoms of EEE in horses include impaired vision, aimless wandering, head pressing, circling, inability to swallow, an irregular staggering gait, paralysis, convulsions and death. Once a horse has been bitten by an infected mosquito, it may take three to 10 days for signs of the disease to appear.

US Department of Agriculture statistics show that in 2012, 209 equine cases of EEE were reported in 19 states, primarily in the southeast and northeast. The USDA 2012 statistics also show that, by comparison, 627 equine cases of WNV were reported in 41 states. “This was the highest number of equine cases of WNV reported in the United States in the past five years, but still considerably lower than the number of cases reported during the 2002 WNV outbreak when 15,257 equine cases were reported,” the USDA report states.

Other states with horses affected by West Nile Virus this year are California with seven cases, plus Wyoming, South Dakota, Texas, Florida, and Ohio, with one case each. These statistics are current as of August 6th. This yields a total of 16 horses from coast to coast before today’s New York case was added.

On the other hand, the government reported 52 cases of EEE in horses this year, before the second Massachusetts case was added. State tallies for EEE include: 25 horses in Florida, 10 in Georgia, 4 in Alabama, and 1 each in Texas, Arkansas and Mississippi in addition to the Louisiana and North Carolina cases.




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