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Scientists Steal Parasite’s Digestive Secrets

By Jan Suszkiw
January 20, 1999

“Stolen secrets” from the barberpole worm may help scientists plot biochemical sabotage to undermine the tiny blood sucker’s mischief in grazing animals like sheep.

The “secrets” include a potent cocktail of digestive secretions discovered in the intestine of the three-centimeter long worm, Haemonchus contortus.

One find, proteins that help the parasite digest red blood cells, may prove vulnerable to new drug control strategies or open the door to animal vaccine research. That’s the hope of zoologist Ray Fetterer and colleagues at the Parasite Biology and Epidemiology Laboratory, operated in Beltsville, Maryland, by the Agricultural Research Service. ARS is the chief research agency of the U.S. Department of Agriculture.

Administering drugs to livestock is the standard course of action against Haemonchus, which feeds on blood from its host abomasum (true stomach). But such chemical control is costly, and the parasite is showing signs of resistance, especially in sheep in the United States and Australia, where scientists are searching for natural alternatives.

Fetterer’s search began with cutting into Haemonchus’ intestine, where hemoglobin and other nutrients are extracted from red blood cells. Along with ARS colleagues Marcia Rhoads and Dolores Hill, Fetterer discovered a key group of proteins, called hemolytic factors, and a cysteine protease enzyme.

Lab analysis showed that the proteins form pores in red blood cells within 30 minutes of contact, causing hemoglobin to escape. The hemoglobin is then broken down into smaller fragments by the cysteine protease enzyme, aiding the worm’s ability to utililize the nutritious blood protein.

Fetterer’s lab is working with Enzyme Systems Products, a Livermore, Calif., company, to see how well substances called inhibitors thwart the parasite’s production of cysteine protease, thus depriving it of a key digestive tool.

A story about the research appears in the January issue of Agricultural Research magazine, and on the Web at:


Scientific contact: Scientific contact: Ray Fetterer, Parasite Biology and Epidemiology Laboratory, Beltsville, Md., phone (301) 504-8300, fax (301) 504-5306,