Resistant Parasites: Predatory Fungus Could Aid Control

Predatory fungus Duddingtonia flagrans might be a viable option for the biological control of infective larvae of small strongyles, researchers noted in a recent study.

Adult small strongyles residing in a horse's large intestine and cecum lay eggs that are passed in the feces. The eggs hatch and larvae develop on pasture. Horses become infected when they ingest the third stage larvae (L3) while grazing.

Administration of deworming drugs, called anthelmintics, is the most common method employed for controlling internal parasites in horses; however, resistance to chemical wormers is a major problem. Small strongyles are already resistant to both of the benzimidazoles (oxibendazole and fenbendazole) and also pyrantel pamoate. There is also evidence suggesting that resistance is developing against ivermectin.

"Alternatives are required to help reduce the continued use of the same anthelmintic class," noted the Brazilian research group in their recent study. "Biological control is among these alternatives, using natural nematode antagonistic fungi."

To evaluate the predatory activity of D. flagrans on L3 small strongyles, researchers incubated the fungus in Petri dishes containing a water-agar combination with or without L3s. The plates were examined microscopically every 24 hours for seven days and researchers counted non-predated L3s.

A significant reduction (93.64%) in the recovered L3s was noted, suggesting that D. flagrans is a potential candidate for the biological control of horses cyathostomin L3.

Martin Krarup Nielsen, DVM, PhD, an assistant professor at the University of Copenhagen in Denmark, commented on the study.

"This is not new," Nielsen said. "This fungus has been tested in cattle, sheep and horses with good, but variable results.

"The fungal spores may not be as efficient as a dewormer, but they will be an excellent alternative. In fact, they will be very suitable for controlling resistant worms and prevent further development of anthelmintic resistance," said Nielsen.

Field studies have been successfully conducted on D. flagrans; however, more research is likely needed before this technique will become available.

"The product was patented in Denmark in the 1990s, but meanwhile the patent has expired and was never exploited," Nielsen said. "I'm still hoping that someone would launch a product--the equine industry needs it!"

The study, "Predatory activity of the Nematophagous fungus Duddingtonia flagrans on horse cyathostomin infective larvae," is scheduled to be published in an upcoming edition of the journal Tropical Animal Health and Production. The abstract is currently available on PubMed.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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