Saturday, November 07, 2009

Deadly EEE virus can affect white-tail deers, horses and humans

The immediate threat is over, but a Middleton vet is urging horse owners to remain cautiously alert for a rare and deadly virus next spring.

Thirteen horses have now died in Nova Scotia as a result of Eastern Equine Encephalitis (EEE). EEE, or sleeping sickness, is a virus that affects the brains of horses and humans. So far this year no horses in Annapolis County have been infected.

Deer hunters in Lunenburg County were asked to help gauge the extent of the virus by obtaining blood samples from deer before Nov. 4. Because the same mosquitoes that attack white-tailed deer also attack horses, it’s hoped that blood samples can help determine the scope of the affected area.

Hunters are being provided a special package to collect the blood samples that are returned to drop-off stations where the samples are screened for EEE by a special field teams of members of the Public Health Agency of Canada. This monitoring program may help identify the extent of the infection in Lunenburg.

Dr. Dave MacHattie, a large animal veterinarian at Middleton Veterinary Services, said that while the number of confirmed EEE cases did sharply rise this year, he doesn’t see any reason to begin immunizing any new horses this season.

“As the weather gets colder and mosquitoes die down for the winter, there’s no point in vaccinating any new horses,” he said. “But in the spring we’ll proceed cautiously with a vaccination program.”

The EEE outbreak remained contained on the South Shore, and no horses were affected in other areas. Horses here that have received the initial dose will be given the second dose. In the spring he’ll proceed cautiously with an immunization program, he added.

These cases are the first confirmed EEE in Nova Scotia, but MacHattie says he’s treated horses with similar illnesses over the past 10 years. These cases are rare and were never confirmed as EEE. This is the first time veterinarians have been to confirm the diagnosis through tests.

MacHattie estimates that about two horses each year are typically affected with similar symptoms. However given such a high incidence rate this year, something has changed and should be monitored closely next season.

The outbreaks of EEE are typically sporadic and unpredictable in the normal course of nature. The disease is believed to be spread between nonmigratory birds by a species of mosquito that generally doesn’t bite horses, or humans, he said. No one knows what causes these mosquitoes to begin biting horses, but every now and then it happens and causes an EEE outbreak.

While EEE is carried by birds and transmitted by mosquitoes, affected birds don't show signs of infection. Unlike infections of West Nile Virus, EEE won't give horse owners a warning by killing birds first.

Infected horses will begin showing signs of being ill about five to seven days after being bitten by an affected mosquito. Symptoms of EEE include sleepiness, or depression; affected horses can have difficulty walking and seem unsteady or wobbly on their feet; seizures, muscle twitches, and pressing their heads against solid objects are also possible signs of infection.

This virus is not contagious between horses. Some stables have required that horses undertake a quarantine period after travelling to an affected area, but this is not a necessary measure, Dr MacHattie added.


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