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West Nile Virus confirmed in two B.C. horses

A Culex quinquefasciatus mosquito is shown on a human finger in this undated handout photograph from the Centers for Disease Control and Prevention (CDC). The Culex quinquefasciatus mosquito has been proven to be a vector associated with transmission of the West Nile virus, according to the CDC.


Two horses in British Columbia's Southern Interior region have tested positive for the West Nile Virus, prompting veterinarians to warn horse owners to have their animals vaccinated.

A veterinarian noticed the symptoms – which include muscle tremors and weak hind legs – in two horses from separate farms over the summer, said John Twidale, chair of the equine committee at the Canadian Veterinary Medical Association's Society of B.C. Veterinarians chapter. One horse was from a farm north of Cache Creek and the other from Ashcroft.

Suspecting the horses had the virus, the veterinarian sent blood samples to a laboratory at New York State's Cornell University, which on Monday confirmed both cases, Dr. Twidale said. The horses are now receiving supportive treatment; one is recovering while veterinarians are less optimistic about the other.

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Dr. Twidale emphasized that while the discovery is significant, people need not worry about transmission of the virus to humans. The virus is most commonly transmitted via mosquitoes and not from animal to person or person to person through casual contact.

"There's no cross-transmission," he said. "It has to come from an infected mosquito bite. It's not an epidemic situation; it's going to be sporadic cases that we have to be aware of. The best approach is vaccination against the disease."

The West Nile virus, an infection of birds, was first identified in Africa in the 1930s. It was discovered in New York in 1999 and has since popped up across the U.S. and in much of Canada, according to the B.C. Centre for Disease Control (BCCDC). The first B.C. cases of the virus in humans and mosquitoes were reported in 2009, with cases of it in corvids and horses in following years.

Confirming the first activity in 2009, B.C.'s provincial health officer, Perry Kendall, said the province had a robust mosquito and West Nile virus surveillance system and that people can take simple and sensible measures to protect themselves from infection.

Most people infected with the disease will never know they had it, according to the BCCDC. Only one in five people bitten by a mosquito and infected with the virus will develop symptoms – which include muscle weakness, memory problems and fatigue in humans – and less than one per cent of those infected will require going to hospital. The fatality rate is about 0.1 per cent.

A vaccination for horses requires only one dose per year and is typically administered in the spring. Veterinarians also recommend the use of fly sheets and face masks for horses, as well as efforts to reduce mosquito populations around barn and pasture areas.

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