Simple Blood Test Could Help Farmers Target Sheep Parasite

A Canadian study of a parasitic roundworm that is increasingly threatening the profitability of the world’s sheep producers could lead to a new diagnostic device to quickly detect the infection days before any symptoms are visible.

“What we are planning to do in the future is something similar in shape to a lancing device for diabetes,” said Dr. Desiree Gellatly, who is a Senior Research Scientist at the Technology Access Centre for Livestock Production (TACLP) at Olds College of Agriculture & Technology.

 “The device would take a drop of blood, and it would indicate whether sheep have the parasite. Producers could pinpoint much earlier, even without animals showing clinical symptoms, which of their sheep need to be treated with dewormers to prevent the parasite from spreading.”

The study found that small molecules called metabolites have the potential to serve as blood biomarkers in sheep for detecting Haemonchus contortus infections – commonly known as the barber’s pole worm, said Gellatly.

Detections can be made up to two weeks before the parasite begins shedding its eggs in sheep feces, she said. “The biomarkers act like a kind of chemical fingerprint as they are specific molecules produced or altered as a result of the host-parasite interaction.”

The finding could pave the way to the creation of a handheld diagnostic device that could allow sheep producers to affordably and accurately test for the worms themselves, she said. This technology could also potentially be used to detect the parasite in other ruminant livestock, such as cattle and goats, pending further research, she added. 

The study was co-led by Dr. Gellatly; Dr. Yaogeng Lei, Research Scientist at TACLP; and Sean Thompson, Director of TACLP, in collaboration with Dr. Ghader Manafiazar of Dalhousie University and Dr. John Gilleard of the University of Calgary.

The life cycle of barber’s pole worms in sheep begins when eggs in feces hatch into larvae during the first two stages (L1 and L2), then develop into infective third-stage larvae (L3) that migrate onto pasture grass during warm seasons. 

Sheep become infected by ingesting L3, which develop into adult worms in the abomasum, or fourth stomach of the sheep, and begin producing eggs after 16 to 21 days. Female worms can each produce as many as 5,000 to 10,000 eggs per day, which are spread through dung in pastures. 

Although adult worms are only up to two centimeters in length, or less than about one inch, they can collectively weaken sheep by attaching to the lining of each animal’s abomasum. 

The parasites feed on blood and can rapidly cause anemia, or lack of sufficient red blood cells to carry oxygen. It not only can affect the profitability of farmers by impacting the ability of their sheep to gain weight or grow wool, but it can also quickly lead to the death of their animals if left untreated, said Gellatly.

“Although the L3 infective stage does not tolerate the harsh winter conditions of Western Canada, we now know that the L4 stage can survive inside the host in a dormant state through a process called hypobiosis. These larvae resume development in the spring, contributing to reinfection even when environmental contamination appears minimal.”

Another pressing issue is the declining effectiveness of commonly used dewormers in Canada, such as ivermectin and benzimidazoles, said Gellatly. “Studies led by Dr. Gilleard’s team have identified the barber’s pole worm as the most prevalent gastrointestinal roundworm in Western Canada, and confirmed the presence of anthelmintic resistance to these treatments.”

The 57-day study was funded by Alberta’s Results Driven Agriculture Research (RDAR) agency, along with Alberta Lamb Producers and Ontario Sheep Farmers. 

It was launched in 2023 and involved testing of Rideau Arcott sheep divided into four groups of 15 animals each: infected and dewormed, infected and non-dewormed, non-infected and dewormed, and non-infected and non-dewormed, said Gellatly. “Testing these groups was essential for identifying metabolomic changes in sheep before and after deworming.”

Producers must currently detect infected sheep using a visual test called the FAMACHA chart. The level of anemia is determined by comparing the colour of the mucous membranes inside of the lower eyelids, or conjunctiva, of the eyes of sheep to the chart. 

Another way producers identify infected animals is by checking for signs such as soiled tails due to diarrhea, as well as “bottle jaw” – a soft swelling under the jaw caused by fluid buildup due to parasite infection. Producers may also confirm infection by sending fecal samples to a lab for fecal egg counts.

The problem is these tests work best on sheep that are already far down the road to being infected, said Gellatly. It is forcing producers to treat all of their sheep with anti-parasite medications such as ivermectin as a precautionary measure, she said.

It not only significantly adds to the expenses of farmers, but it also is increasingly causing the infections to become harder to treat, she said. “The worms are developing resistance to these medications due to overuse.”

In summary, this study marks a major advancement in combating parasitic infections in sheep by offering a practical, science-based approach to a growing global issue. 

Through the identification of metabolite-based biomarkers, it has the potential for an early, accurate, and on-farm detection of Haemonchus contortus, paving the way for more targeted parasite control, reduced reliance on mass anthelmintic treatments, and enhanced animal welfare. 

With further development, the proposed handheld diagnostic device could become a vital tool for producers, supporting the long-term sustainability and profitability of the sheep industry.