A recent outbreak of a mosquito-borne virus affecting sheep flocks across southern and eastern Ontario has researchers puzzled.
The widespread virus, called Cache Valley virus, affects pregnant ewes which then miscarry or give birth to deformed lambs.
“[Mosquitos] can feed on anything, they can feed on us, they can feed on cattle, anything, but most species don’t develop disease and with sheep the only time that we know that they’ve been infected is if they are infected for the first time when they are in early pregnancy,” said researcher and professor at the University of Guelph Dr. Paula Menzies.
She explained the virus affects the forming fetus. If it infects the lamb during its first 25 or 26 days, the fetus usually dies in embryo.
But if the fetus is infected between its 25th or 26th day and 48th or 49th day, it will develop malformations.
Menzies explained the deformations include twisted legs and fused joints, scoliosis in the spine, decreased muscle tissue and cavitation in the brain. “Their malformations are pretty terrible, pretty severe,” she said.
While Cache Valley virus can be found all over North America, this year saw a jump in the number of lambs born with deformities in southern and eastern Ontario.
On one farm, 19 of 60 lambs born were deformed and they had another 12 that did not lamb at all, said Menzies. She added lambs born over Christmas and into early January tend to be infected.
While Menzies was clear that West Nile and Cache Valley are not the same disease, they are both mosquito-borne and they see more of the virus later in summer and into early fall when the ewes are being bred for Easter lambs
While the actual cause of this outbreak is unknown, Menzies said there are some theories. It could be a new strain of Cache Valley or maybe the warm fall contributed to more sheep infected.
There is no vaccine for Cache Valley. Menzies said there are some preventative measures, such as not breeding during the high mosquito season, not having standing water or keeping the flock in a pasture rather than a dry lot or in a barn.
“It’s one of the diseases that we have to be concerned about,” said Menzies.
She explained her team would be researching the disease this fall along with the Canadian Public Health Agency.
The agency is “very interested because this virus can infect humans,” said Menzies.
“It’s what we call a weak zoonotic disease; lots of people probably get infected and never get sick. Occasionally people get quite sick.”
In a 2015 Canada Communicable Disease Report, the public health agency explains there is potential for an infection of humans, but there is a need for more research.
“The strain of Cache Valley virus isolated from a recent human case in the U.S. was almost identical to the isolates obtained during the sheep outbreaks in Québec and Ontario, indicating that currently circulating genotypes of the virus do exhibit the potential for pathogenicity in humans and other animals,” stated the report.
At this point, Menzies said there haven’t been any reported deformities in any other type of livestock due to Cache Valley.
