Live­stock dis­ease wing­ing its way north as cli­mate warms

The Woolwich Observer - - VENTURE - FIELD NOTES

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.

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