Duddingtonia flagrans sounds like a character from the BBC television series “Downton Abbey” or perhaps a variety of English tea rose. Instead, it is a species of carnivorous soil fungus that shows promise in managing intestinal nematode (“worm”) infestations on both organic and conventional dairies.
Resistance to synthetic antiparasitic products is now so widespread that the use of synthetics alone in control of parasites is considered unsustainable. It is of such concern that Ireland has recently made synthetic antiparasitic drugs prescription-only in food producing animals. Control of internal parasites is best accomplished using an integrated approach that combines selective targeted use of synthetics in clinically affected animals, pasture management, and biological controls such as carnivorous fungi.
Trapping nematodes
Danish scientists first reported on clinical applications of so-called nematophagous (“worm-eating”) fungi in 1993. In particular, the fungus D. flagrans is found in nature in pasture manure pats. Reproducing through the spread of chlamydospores (inactive or “resting” spores), they form, as most fungi do, a vegetative mycelium, or complex network of filaments that collect water and nutrients from the soil. Unlike other fungi, this species also creates trapping devices that snare and kill nematodes. By-products of decomposition of the worms are then used as a food source.
The biology of nematophagous fungi has been studied in horses, goats, and cattle. Experimentally, feeding or drenching the animal with spores for several days to weeks results in a spillover or inoculation of manure pats. Once defecated, the spores germinate and begin to form worm-trapping filaments. The spores do nothing while inside the animal; their parasiticidal work is all done outside, in the pasture. In theory and practice, continued feeding of the spores eventually reduces the number of infectious larvae in the environment. Over time, worm loads, including the harmful HOT complex (hemonchus, ostertagia, and trichostrongyles) of worms should decline.
Makes a difference
A 2017 scientific report in the journal Experimental Parasitology relates a trial in grazing 8- to 12-month-old Brown Swiss/zebu-cross calves conducted in tropical Mexico. Calves were drenched with a spore-containing solution every other day for 30 days. The treatment resulted in fewer nematode larvae in manure and a significant reduction in larvae in grass. More recent studies have shown high effectiveness — 60% to 99% reduction in larvae counts — in cattle.
Commercial applications of this novel therapy are most welcome. Two pelleted forms of D. flagrans chlamydospores with a long shelf-life, one from an Australian company and a second from a Brazilian firm, are currently available. To reduce labor and ease administration of spores, work is currently underway on sustained-release rumen boluses and spore-infused energy blocks. Both organic and conventional graziers should ultimately benefit from this innovative form of biological control of medically significant nematodes.
250425_195
