Livestock disease winging its way north as climate warms

FLYING, BITING MIDGES, SOMETIMES called nosee-ums – are a scourge to wildlife. Hunters in our area recognize their effects on deer in particular, which are highly susceptibile to a group of midge-transmitted viruses.

Now 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.

Here’s why. 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. But University of Guelph PhD student Sam Allen, who is studying the midge as a disease vector with her supervisor Prof. Nicole Nemeth in the Ontario Veterinary College, says in recent years, 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 whitetailed 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’s 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’s 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.

There’s no evidence this disease affects humans. But Allen think the midge’s arrival in Ontario, and the death of the deer in London, should be on farmers’ radar.

“As environments are become increasingly shared between humans, livestock and wildlife, there is an increased risk of pathogen spread among these groups,” she says. “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.