Sheep in pasture

Researchers have discovered a treatment that could combat the No. 1 health problem in the U.S. sheep industry: Haemonchus contortus, a parasite that infects the stomachs of ruminant animals, often leading to death.

WASHINGTON, D.C. — A group of researchers Wednesday announced a groundbreaking new treatment against parasites in sheep and other livestock, potentially preventing anemia, weight loss, poor meat and wool production, fertility problems and death.

The treatment could combat the No. 1 health problem in the U.S. sheep industry: Haemonchus contortus, a parasite that infects the stomachs of ruminant animals, often leading to death.

The team included researchers from USDA's Agricultural Research Service, the University of Massachusetts and Virginia Tech.

"H. contortus is one of the most devastating parasites on earth for small ruminants, so obviously, these are incredibly exciting results," said Raffi Aroian, lead researcher and professor at the University of Massachusetts Medical School.

ARS microbiologist Joe Urban, another lead researcher, said he has worked for decades trying to combat parasites.

"It's frustrated me my whole career, so it's exciting to finally make progress," he said.

Scientists say H. contortus has developed resistance to virtually all known classes of anti-parasitic drugs. Anthelmintic resistance, or dewormer resistance, is a major problem for U.S. sheep and goat producers.

This treatment, researchers say, uses a different mode of action, employing Bt protein crystals.

Bt stands for the naturally occurring bacterium Bacillus thuringiensis, which lives in soil worldwide. Some types of Bt produce protein crystals. Some of these crystals are toxic to insects and are used to control pests in organic crops. Other crystals are toxic to nematodes, or roundworms.

In this study, the researchers found that using a Bt crystal protein called Cry5B kills parasites in small ruminants. Cry5B is most effective in a para-probiotic form, meaning the live bacteria are inactivated but their crystals are preserved.

In early tests, infected sheep treated with the para-probiotic experienced 90% reductions in fecal egg counts, 73% reductions in parasite burdens and a 96% reduction in the number of female parasites.

"It's certainly effective in killing worms," said Anne Zajac, professor of parasitology at Virginia Tech's Virginia-Maryland College of Veterinary Medicine.

The researchers say they expect a commercial product won't immediately be available.

Aroian said "validation studies" are finished, but the new treatment still needs to go through preclinical studies, clinical trials and U.S. Food and Drug Administration approval. A large-scale manufacturing partner that declined to be named is already lined up.

Research funding is limited for niche industries like small ruminants, so Aroian said he and his co-researcher, Gary Ostroff, will need to raise $100,000 for preclinical studies.

Researchers say the discovery may also help fight parasites in other livestock. Early trials with horses, pigs and other animals have been successful.

The researchers said their finding may even revolutionize human medicine by treating people who suffer parasitic infections in the developing world.

But Zajac of Virginia Tech warned that if the new treatment is developed commercially, it is crucial producers don't rely on it exclusively because worms could develop resistance to Bt.

Producers, Zajac said, should use the new treatment "wisely within integrated parasite management programs" including parasite pasture management, planting antiparasitic forages, rotational grazing, breeding management and targeted rather than blanket deworming.

"Certainly, if this becomes a commercially available product, we have to be really, really careful in how we use it," she said.

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