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.
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.
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.
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.