Livestock seen threatened as biting insects press north

Culicoides sonorensis. (Scott Bauer photo courtesy ARS/USDA)

Bluetongue’s most recent appearance in the Canadian cattle herd may be a taste of what’s to come as insect species expand northward, a new study warns.

Anna Zuliani, previously a graduate student in veterinary medicine at the University of Calgary (UCVM), recently published a paper on how geographical distribution of biting midges relates to the disease cycle in different wild and domestic animals.

According to the paper, published in the online journal PLOS One, wild and domestic animals in Canada are at higher risk of disease as biting midge are likely to make their way northward from the U.S. due to climate change.

Bluetongue and epizootic haemorrhagic disease (EHD), spread by biting midge, so far are endemic in the U.S. but turn up “only sporadically” in livestock and wild animals in Western Canada, the university noted.

Bluetongue, previously seen in Canadian cattle only in British Columbia’s Okanagan valley, turned up in August and September in three cattle in southwestern Ontario’s Chatham-Kent municipality, leading several of Canada’s trading partners to cancel export certificates for live Canadian cattle and/or genetics.

“The midge is a key actor in disease transmission,” Zuliani said in a Calgary release. “The presence of the midge at northern latitudes is likely to increase the probability of haemorrhagic disease in wild and domestic ruminants.”

Zuliani and the other researchers used 50 “presence points” for the midge (Culicoides sonorensis) collected in Montana and south-central Alberta between 2002 and 2012, along with monthly climatic and environmental predictors, to develop a series of “maximum entropy distribution models.”

By studying the geographical distribution of the midge and how it relates to the disease cycle in different animals, Zuliani and the team could predict an increase in risk of disease spreading.

The team’s projections showed the areas predicted to be at “moderate-high” probability for biting midge occurrence would increase from the baseline scenario to 2030, and again from 2030 to 2050, for each “representative concentration pathway” studied.

The projection also showed the northernmost limit of biting midge distribution is expected to move northward during that time to above the 53rd parallel — that is, up around communities such as The Pas, Man., Prince Albert, Sask., and Edmonton.

“Knowing the current and potential future distribution of the disease vector will help setting up a cost-effective disease surveillance plan in the province,” said Zuliani, now in PhD studies at Italy’s University of Udine.

Such modeling, she said, “will help farmers to identify risk early, allowing measures to be put in place to prevent severe disease outbreaks and reduce their connected economic cost.”

Recent observations of midge-borne EHD outbreaks in northern Montana and southern Alberta “supported our projections and considerations,” the research team said in their paper.

Data from the model as developed has also been used by the Canadian Food Inspection Agency to help predict risk to cattle across the Prairies, the university said.

“This paper will inform policy with regard to vector-borne diseases and climate change in North America and we hope that it will be well worth citing in years to come,” Susan Cork, head of UCVM’s ecosystem and public health department and a co-author of the paper, said in the same release. — Network


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