Livestock disease winging its way north as climate warms

Flying, biting midges (Culicoides spp.) — sometimes called no-see-ums — are a scourge to wildlife. Hunters recognize their effects on deer in particular, which are highly susceptibility to a group of midge-transmitted viruses.

But there are growing concerns about their potential effect on livestock, too.

Here’s why. A midge swarm will blood-feed on animals, causing irritation, potential blood loss or worse. Besides the pain they inflict through their bites, midges also carry and spread harmful viruses that can lead to diseases called epizootic hemorrhagic disease (EHD) and bluetongue.

Both diseases can be fatal in deer; the latter is especially concerning in sheep. They can also affect cattle, causing the animals to develop lethargy and general malaise, impacting productivity.

At least 1,200 species of Culicoides spp. midges have been identified globally. This particular species, C. sonorensis, has been confirmed as a vector of these viruses, which are historically found in the southern U.S. and have also been detected in parts of western Canada.

However, researchers have started issuing warnings about the windborne midges’ movement from the U.S. into Ontario.

A good wind can blow a midge swarm as far as 700 kilometres, in just a few days. And thanks to climate change, once the midges arrive, they have a warmer climate in which to survive.

“Historically, outbreaks have occurred every 10 or more years in northern zones,” says University of Guelph PhD student Sam Allen. She’s studying the midge as a disease vector, along with her supervisor Nicole Nemeth in the Ontario Veterinary College. “In recent years, though, these northern outbreaks seem to be occurring more frequently — every five years or so. The reasons for this are unknown, but many scientists believe that climate change is involved.”

C. sonorensis was first identified in Ontario in 2013. In addition, in 2015, three resident cattle were found to have antibodies against bluetongue virus, suggesting they’d been exposed locally to the disease.

The situation has intensified. Last month, in conjunction with Allen’s field studies, the Canadian Wildlife Health Cooperative diagnosed two white-tailed deer from around London that died from EHD. The cause of death was confirmed by Canadian Food Inspection Agency (CFIA) in Winnipeg. Up to that point, in Canada, no animal deaths east of Alberta had been attributed to EHD.

In the field, Allen has been receiving cooperation from the farming and hunting communities. Since the spring, she has worked with 11 beef and sheep farmers in southwestern Ontario and in the Grey-Bruce region to monitor the incidence of C. sonorensis and the diseases it may be spreading. She has also connected with hunting groups to make them aware of her study.

On each farm, Allen set insect traps and took blood samples from livestock. This fall, she and Nemeth are analyzing the samples in conjunction with collaborators at the CFIA, and want farmers to be aware of this new development.

“This insect’s arrival in Ontario and the death of these deer should be on farmers’ radar,” says Allen. “As environments are become increasingly shared between humans, livestock and wildlife, there is an increased risk of pathogen spread among these groups. That means it’s important to gain a better understanding of the factors that contribute to risks of pathogen infections.”

She says this understanding will contribute to better predicting and possibly managing disease spread, to safeguard the health of livestock and others.

Allen notes there is no evidence that this disease affects humans. However, individuals handling sick or dead animals should wear protective clothing, gloves and wash their hands thoroughly. Anyone who sees a sick or dead deer should contact the Canadian Wildlife Health Cooperative or Ontario’s Natural Resources Information Centre.

The Southeastern Cooperative Wildlife Disease Study at the University of Georgia is also involved in the research, which is funded by the Ontario Ministry of Agriculture, Food and Rural Affairs – University of Guelph Partnership. Additional support is provided by the Ontario Sheep Marketing Agency, the Ontario Federation of Anglers and Hunters and the Quality Deer Management Association.