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Worm vaccine works from the inside out
By Charmain Tan Courcelle
MISSISSIPPI STATE -- The search for an economical means to produce a parasite vaccine for livestock led a Mississippi State University researcher to look at the guts of the problem.
Cody Coyne, a researcher with MSU's College of Veterinary Medicine, has developed a method for growing intestinal cells from nematode parasites for use in vaccines.
Haemonchus contortus, known commonly as the barberpole worm, infects the true stomach of cattle, sheep and other ruminants. Infection with this worm can decrease animal productivity and is potentially fatal. Left unchecked, parasite infestations can lead to great economic losses in the livestock industry.
"In the past, drugs called anthelmintics were used to kill parasitic worms," Coyne said. "But in some areas of the world where there is intensive use of these drugs, there is a serious problem with drug resistance."
Coyne thought the use of vaccines would be a good alternative to drug use if a suitable immune target could be identified. Protective immunity against internal parasites depends on direct contact between the host animal's immune system and a vital organ system in the parasite.
"Some antibodies produced by the immune system cannot exert a protective effect because they are unable to move across the worm's external cuticle layer," he said.
An Australian team's success with a vaccine preparation harvested from the digestive tract of living ticks led Coyne to consider a cell-based vaccine for barberpole worm.
"To use this approach, we had to develop the technology for isolating and growing parasitic cells," Coyne said. "This meant that we had to isolate a source of purified, living parasites from a ruminant's stomach contents and design growth conditions to select for intestinal cells."
Once he had candidate cell populations, Coyne used biochemical and molecular biological tests to identify the cells and determine whether they came from the barberpole worm's digestive tract. These tests enabled him to confirm that he had isolated H. contortus intestinal cells.
Field trials conducted by Coyne and a pharmaceutical company have shown the cells are effective as a vaccine in livestock.
Coyne said one target for the host animal's immune system appears to be an enzyme involved in worm digestion. Parasites feeding on a vaccinated animal ingest antibodies to this enzyme, which hinder the barberpole worm's digestive system, starving the worm.
The parasite vaccine could help the livestock industry protect animals from barberpole worm infections, Coyne said. An additional benefit from the vaccine is prolonged protection from worm parasites that can be passed from mother to offspring at birth.
Coyne received a patent for his technique for growing nematode parasite intestinal cells in a laboratory environment. His group has isolated cells from 14 different species of internal parasites that affect multiple breeds of domestic animals.
For more information, contact: Dr. Cody Coyne, (662) 325-1120