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Ground-Breaking Treatment Prevents Parasites in Sheep

By   /  December 14, 2020  /  No Comments

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The U.S. Department of Agriculture’s Agriculture Research Service (ARS) has developed a groundbreaking treatment for barber’s pole worm (Haemonchus contortus), the number one health issue in the sheep industry. In live-animal trials, the new treatment reduced fecal egg counts by 90% and overall parasite burdens by 72%. Perhaps most importantly, the treatment impacted female parasites the most, reducing their populations by 96%. Such a large reduction in females means an equally large reduction in the number of eggs produced, leading to reduced infections overall.

Female worms have a red and white striped appearance, from which the common name ‘barber’s pole’ worm is derived. Barber’s pole worms are the highest egg producers of all sheep worms — females can lay up to 10,000 eggs per day. Photo courtesy of CSIRO

The Problem

Haemonchus contortus (Barber’s pole worm) is a parasitic roundworm that sucks blood from the lining of the sheep’s stomach. This causes anemia, bottle jaw (a swelling under the jaw), reduced milk production, weight loss and reduced wool growth and quality. Severe infections can be deadly. The worm parasite mates within the animal and its fertilized eggs per day pass through the animal’s waste into the soil. The larvae then develop to re-infect other unsuspecting animals, spreading the infection throughout a pasture and creating a cycle of infection. Since the female barber’s pole worm is the highest egg produceer of all sheep worms, laying up to 10,000 eggs per day, the scope of the problem can be huge.

A Solution From the Soil

The H. contortus parasite has developed resistance to virtually all known classes of anti-parasitic drugs, leaving producers with few solutions. But ARS researchers, and their partners at Virginia Tech and the University of Massachusetts’ Medical School knew of a naturally occurring protein made by a bacterium that held promise. Bacillus thuringiensis (or Bt) is a soil-dwelling bacterium that, as part of its life-cycle, produces crystal proteins. These crystal proteins (Cry5b) bind to and disrupt the integrity of the invertebrate gut, ultimately killing it. These proteins have been widely and safely used around the world as a bioinsecticide and a treatment for gastro-intestinal nematodes in non-ruminants and humans. But it was unclear, until now, if it would work against H. contortus, or if it would work in a ruminant.

Photomicrograph of IBaCC showing inactive Bt cells and encapsulated crystals (dark inclusions). Photo from Figure 3 of the published paper.

Testing a Hypothesis

The researchers first ran tests to see if Cry5b was effective against H. contortus. When it was successful, they took the next step – putting the protein into a form that could be administered to live animals. They created a “para-probiotic” from an inactive Bt cell wall that could contain fully active Cry5b. The result, IBaCC (Inactivated Bacterium with Cytosolic Crystal), worked when tested on eggs, in ruminal fluid, and when given to sheep infected with H. contortus.

The figure below, taken from the published paper shows how effective the treatment was in reducing fecal egg counts in infected sheep. There was a rapid and dramatic reduction of parasite reproduction and survival, without any negative effect observed in the sheep.

 

Research Continues

While IBaCC was effective in sheep, results were not as successful in goats. Cry5b did work on eggs obtained from infected goats. But when a different form of the crystal protein was administered to the goats themselves, it did not significantly reduce parasite loads. Researchers don’t yet know the reasons for the differences but, as noted in the paper they could include:

1) differences between goats and sheep;
2) differences in dosing (2 × 40 mg/kg versus 3 × 60 mg/kg); and/or
3) differences between the treatment form the goats received and the IBaCC administered to the sheep.

Researchers did conclude that “Cry5B IBaCC has significant potential to augment current control strategies against H. contortus infections in sheep and to overcome parasite resistance to drugs currently used to control this important parasite of ruminants.” The treatments are currently under review by the U.S. Food and Drug Administration and will likely be commercially produced in large amounts once approved.

This project was supported by the National Institutes of Health/National Institute of Allergy and Infectious Diseases; and the Agriculture and Food Research Initiative Competitive Grant from the USDA’s National Institute of Food and Agriculture.

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About the author

Publisher, Editor and Author

Kathy worked with the Bureau of Land Management for 12 years before founding Livestock for Landscapes in 2004. Her twelve years at the agency allowed her to pursue her goal of helping communities find ways to live profitably AND sustainably in their environment. She has been researching and working with livestock as a land management tool for over a decade. When she's not helping farmers, ranchers and land managers on-site, she writes articles, and books, and edits videos to help others turn their livestock into landscape managers.

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