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article imageIs Cache Valley virus evolving? Ontario sheep farmers worried

By Karen Graham     Mar 23, 2016 in Health
Ontario veterinarians are concerned over an outbreak of a disease affecting sheep caused by a little known mosquito-borne virus called Cache Valley virus. Their concerns are heightened because the virus also can pose a risk to humans.
The world has seen a number of viruses pop up over the last few decades. Many of them are relatively new to us, and are carried by mosquitoes. Vaccines for most of these new viruses haven't even been developed yet.
Like the Zika virus, the Cache Valley virus in Ontario is also linked to birth deformities, but in sheep. And while the Cache Valley virus is now considered to be endemic in Canada, there is some concern because this year's outbreak is the largest seen in recent memory.
And according to The Star, as with the Zika virus, we will more than likely be just as unprepared.
“Cache Valley is not very well understood at all. It was kind of ignored for a long time,” said medical entomologist Philip Armstrong, who studies the virus and conducts mosquito surveillance for the Connecticut Agricultural Experiment Station.
Ontario Christmas not happy for sheep farmers
Veterinarian Paula Menzies, who also happens to be a professor at Guelph University. says the first signs of trouble came to Ontario around Christmas. “Veterinarians were sending (us) these deformed fetuses and I got an email from a couple of (sheep) producers saying, ‘This is happening on my farm. What the heck is this?’”
A Texas laboratory confirmed Menzies' suspicions when test results showed it was the Cache Valley virus. The virus popped up in Ontario sheep farms in 2011, 2012 and 2013, reports Better Farming. But it was the latest outbreak, in December 2015 that has people worried.
Menzies says that previous "outbreaks didn't tend to be very severe." Farmers usually might report two or three deformed lambs, but that was all. She started an online survey to find out the extent of the outbreak, but says, "It’s certainly the largest that anybody that I’ve worked with is aware of." Menzies knows of at least seven affected flocks. “The question is why?”
Culiseta inornata. Winter mosquito.
Culiseta inornata. Winter mosquito.
South Carolina/Gov.
Cache Valley virus - What we do know
Cache Valley was discovered during a routine mosquito surveillance study in August 1956 In Utah. The mosquito, named Culiseta inornata collected in a pool of water under a bridge was carrying the unknown virus. It had never been seen before. Mosquitoes in the genus Culiseta are adapted to cold weather and are sometimes referred to as a "winter mosquito."
The mosquitoes are known to feed on birds, mammals, humans and occasionally, reptiles. As for the extent of the risk to human health, other than knowing they do feed on humans, little else has been known until very recently. The Zika virus is very similar in this case because little was known about it until it was too late.
One important thing to know: the two viruses are very different. Cache Valley belongs to the Bunyaviridae family while Zika is a flavivirus. What is similar between the two is that they are both spread by mosquitoes and both will usually cause asymptomatic infections, and they lack any vaccine or treatment.
The Cache Valley virus belongs to the family  Bunyaviridae .
The Cache Valley virus belongs to the family, Bunyaviridae .
Cell Biology
We do know that mosquitoes can transmit the Cache Valley virus through biting humans. Humans cannot get the disease directly from animals. To date, three documented cases of Cache Valley have been seen in the U.S., with the cases resulting in meningitis, encephalitis, and one death.
Like Zika, the Cache Valley virus is actually more predominant than we suspected. A 2012 study in Mexico found that 18 percent of 823 patients treated for fevers were carrying Cache valley antibodies, meaning they had been previously exposed to the virus.
In June 2015, Public Health Agency of Canada (PHAC) conducted a survey of West Nile virus patients in Saskatchewan and Manitoba, finding between five percent and 16 percent of those tested had antibodies against Cache Valley.
PHAC does say that with illness caused by Cache Valley, supportive care and the management of complications, such as relieving increased intracranial pressure is needed. PHAC also states: "There is now sufficient evidence to indicate that when patients present with febrile and neurological disease and a history of exposure to mosquitoes, both West Nile virus and mosquito-borne bunyaviruses (Cache Valley) should be considered."
There is evidence that the Cache Valley virus is evolving, and this may not be good. In 2015, Armstrong published a study that evidenced a new strain of the virus that apparently originated in Mexico. The same strain popped up in Connecticut in 2010 and has since that time become the dominant strain.
That same strain was the cause of the Cache Valley outbreak in Ontario in 2011, and possibly the latest one too (Antibody testing confirmed the virus but it is yet to be isolated). Michael Drebot, with PHAC, said there is evidence the virus is growing a little faster and "replicating more efficiently."
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