A team of researchers has demonstrated that when a bacteria-derived protein was fed to worm-infected swine, the infection was nearly completely eliminated.
Intestinal parasitic roundworms are host-species specific and are found in pigs, cats, dogs, humans, and other animals. A roundworm specific to humans, Ascaris lumbricoides, is rarely seen in developed countries. Still, about 1 billion people are infected with this species of worm worldwide, usually via some contact with feces. When A. lumbricoides infects children, nutrient deficiency, respiratory distress, stunted growth, and immune defects occur. In the extreme, infection can cause life-threatening gut blockage. Worms can also migrate into the bile ducts and the permeable membrane that covers the abdominal organs.
The parasitic roundworm that commonly infects pigs is Ascaris suum, which is so genetically similar to A. lumbricoides that some evidence suggests they are the same species. A. suum infection in pigs is considered a good model for A. lumbricoides infection in humans because of its similar migration through the body and to the intestines.
The research team included microbiologist Joseph Urban and his colleagues at the Agricultural Research Service’s Beltsville [Maryland] Human Nutrition Research Center and Raffi Aroian and Yan Hu at the University of California-San Diego.
In its experiments, the team used a crystal protein called “Cry5B,” provided by Aroian’s group, which is derived from the soil bacterium Bacillus thuringiensis. Cry5B protein is considered nontoxic to vertebrates and mammals, but it has been used in the past as an insecticide. A. suum genetically expresses receptors for Cry5B.
Previously, Cry5B had been shown by Aroian and colleagues to be toxic to hookworms. In laboratory tests, Cry5B triggered activation of stress-response pathways in Ascaris larvae and adults similar to that observed with other worms.
“Feeding two moderate doses of Cry5B to pigs resulted in nearly complete elimination of intestinal A. suum infection, and all intestinal roundworm larvae were damaged or destroyed,” says Urban. “The dosage we provided in this study is comparable to the dose range used in existing commercial antiparasitic drugs.”
There is a need for more practical delivery systems for antiparasitic drug treatments, according to the scientists. Cry5B holds potential for use where worm resistance is becoming a problem, especially among ruminant livestock. The University of California researchers have filed a patent application on the protein expression, and further cooperative research with ARS is being planned.
“These results show the potential of Cry5B to treat Ascaris infections in pigs and other livestock and to work effectively in the human gastrointestinal tract,” says Urban.
More information can be found in an article published in the June 2013 issue of PLOS: Neglected Tropical Diseases.—By Rosalie Marion Bliss, Agricultural Research Service Information Staff.
This research is part of Animal Health, an ARS national program (#103) described at www.nps.ars.usda.gov.
"New Class of Animal Deworming Agent" was published in the May/June 2014 issue of Agricultural Research magazine.