Some parasite battles won, others still need fighting

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The fight against parasites is nothing new, but once one is defeated, it seems another moves in to take its place. It’s an ongoing battle that Eugene Janzen, professor and the assistant dean of occupational practice at the University of Calgary College of Veterinary Medicine, remembers well.

“I’m an old man, and when I was a child driving from Manitoba to B.C., one of the things that everybody would notice is a sign at the side of the road that said, ‘This is a warble-free area.’ That was the first parasite that producers in Western Canada ever had to deal with, and we’ve driven that parasite almost out of existence,” he said.

Warble flies are large, and as they would descend upon a herd of cattle, they would start to panic and run away with their tails held over their backs. The strange behaviour was called “gadding” and for a cattle producer, it spelled disaster. The flies would lay eggs on the legs, which were licked and ingested by the bovine. Once inside the body, they would migrate under the skin along the backbone, causing swellings and bumps called warbles.

“They’d be like the size of a toonie, and they’d have a little hole in them, and if you really wanted to gross yourself out, you would squish that lump and lo and behold, something about half the size of your little finger would pop out — it was a warble larvae,” said Janzen.

The larvae caused a lot of muscle and hide damage, but it’s nearly been entirely eradicated now, thanks to ivermectin and other warble treatments.

Pour-on effectiveness

The Rocky Mountain wood tick used to strike fear in the hearts of ranchers in B.C.’s dry interior south of Kamloops. The ticks release a neurotoxin into the cattle, causing paralysis. “You’d come across the animal and it was terrifying, it was like a dishrag and if you got to it before the ravens and the coyotes did, you were lucky. And if the ravens and coyotes got there first, they would peck the eyes out of the live animal, or eat off the tongue,” Janzen said.

Today, most ranchers apply ivermectin in the fall at roundup, and it is effective in preventing many such parasite problems. However, Janzen said evidence is accumulating to show that pour-on application isn’t as effective as injecting the treatment. “I think we’re beginning to see it’s not working quite as good as it should be,” said Janzen, adding that topical treatment doesn’t deal as efficiently with the internal parasites like intestinal and stomach worms.

Liver flukes

Though ranchers do not have to fear the warble flies any longer, they need to know about a new threat — the fluke. “Wild ungulates have a parasite that migrates through the liver. It’s called a fluke and it turns out there are several species of fluke and some are worse than others,” Janzen said. “What is important to know is that when domestic animals and wild animals share the same environment they probably also share parasites.”

The fluke is commonly picked up in wetlands, or near bodies of water or from moist soil. The larvae is then picked up by the grazing animal, is absorbed by the stomach and then migrates to the liver.

“They can do terrible damage to the liver, and then they can often develop a secondary infection which is where the losses occur,” said Janzen.

The parasite is found throughout most of Western Canada, though some spots are worse than others.

“It’s in the areas where we have an abundance of wild animals, so the foothills, places like the Cypress Hills, places like some of the river valleys where we would have more wild ungulates is where we could expect this transfer to occur,” Janzen said.

Producers need to know what parasites their cattle are at risk for, and discuss specific treatments or preventions with their veterinarian. Ivermectin has been literally a lifesaver, but it’s not going to be effective on flukes. “One-stop shopping does not look after them all,” said Janzen.

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