Tropical parasite bringing ‘sudden death’ to Canadian farmers’ sheep

The barber’s poll worm has been wreaking havoc on sheep farmers’ livestock in recent years. Photo/Andrew Peregrine

When B.C. farmer Susan Russell suddenly lost a sheep to a deadly parasite, she knew she had a problem.

But it wasn’t until she heard from other sheep farmers who were experiencing similar problems that she realized the extent of the predicament.

Sheep farmers across the country have been losing lambs and ewes to a tropical parasite, known as the barber’s pole worm, or haemonchus contortus. Researchers say the worm has existed in Canada for decades, but the parasite’s population has flourished in recent years partly because of warmer weather.

“This has definitely become a major problem for producers,” said Russell, who has farmed a small flock of sheep for decades. “We’re all finding that it’s impacting how we can raise sheep.”

These worms usually measure around two centimetres and grow to adulthood in the digestive tract of sheep. Their larvae die off in the winter when the temperature goes below freezing, but thrive in the summer when it’s hot and wet and can live for months before being ingested by sheep.

When the worm’s reach adulthood, the worms drain the blood and protein out of the host sheep, which then die.

The worm’s population can grow very quickly, depending on how warm and wet the summer is, said Dr. Paul Menzies, a professor at the veterinary college at the University of Guelph. A farm can very quickly go from having no parasites on it to having animals dying from an infestation, she said.  

“The warmer and wetter our summers are, the more issues we’re going to have with haemonchus,” said Menzies.

Warmer summers and longer grazing seasons in recent years have given the worms more opportunity to build up massive populations, she said.

While researchers and farmers blame climate change for creating conditions in which the worms have thrived, a resistance some worms have to drugs that farmers use deworm sheep is compounding the problem. If a farmer deworms all of his or her sheep during the winter in the barn, they will be exposing all of the barber’s pole worms on the farm to the drug, as the parasite can’t live out on pasture during the winter.

The worms who survive the deworming will only be the ones who are resistant to the drug and there will not be others left to compete with them, Menzies said.

The parasite can be very deadly quickly after infection. Farmers can deworm their sheep and then see them die less than two weeks later because so many have been surviving the deworming drugs, Menzies said.

The parasites can also be hard to detect. While most worms cause animals to have diarrhea, barber’s pole worm does not. The only known way to check for the parasite is by looking at the inside of the lower eyelid to see how pale it is. 

“We call it sudden death because these are often not sheep that look sick, but they can go from being fine to almost completely dropping dead,” said Menzies.

Researchers check a lamb for barber’s poll worm. Photo/Chanel Schwartzentruber

Gwyneth Jones, a sheep farmer who also teaches at St. May’s University in Halifax, N.S., stumbled across the problem in 2012, when she invited some of her students to conduct research on her own sheep at her farm on the Bay of Fundy.

By examining sheep faeces, the students found that the number of the parasite’s eggs on her pasture had sky rocketed since the last time Jones had conducted such research in 1997.

Jones said she was lucky to catch the problem early enough that she was able to closely monitoring her sheep for the parasite, but it has been devastating for others, who have lost many animals to the worm.

It was particularly devastating for many sheep farmers in 2012, 2013 and 2014, Jones said.

“I know a number of particularly new entrants were discouraged and gave up fairly quickly. I know a number of people gave up raising sheep in those years,” she said.

Researchers have been developing techniques for farmers to lower the risk of the parasite developing on their farm. Some of these include only deworming sheep when necessary and to closely monitor them for the parasite.

Researchers have also been working to develop new drugs that the parasites are not resistant to.

“In general, it certainly was and continues to be a serious issue, but now people are much better informed about what’s going on and understand the importance of weather conditions,” said Jones.