Research carried out in Denmark could well provide a breakthrough in the control of worms in horses.
Anthelmintic resistance is becoming more widespread worldwide. In particular the cyathostomes (small red worms) have shown a great ability for developing resistance to the benzimidazole group of anthelmintics ("wormers"). Resistance to pyrantel has also been reported. Consequently alternative worm control strategies are being investigated. One method showing promise is the use of a fungus that attacks the free-living larval stages of parasitic worms and so reduces the number of infective larvae on the pasture.
The fungus Duddingtonia flagrans has been shown to trap the free-living stages of roundworm ("nematode") parasites, such as cyathostomes. It grows rapidly in fresh faeces and its chlamydospores (resistant spores) are able to survive the passage through the gastro-intestinal tract of the horse. These fungal spores have no effect on the animal and only germinate once passed in the faeces where they develop into nematode-trapping fungal nets.
In the study carried out at the Royal Veterinary and Agricultural University`s farm near Copenhagen a new isolate of the fungus Duddingtonia flagrans (called "Troll A") was used as a biological control agent against the free-living larval stages of horse strongyles.
A horse known to be carrying a mixed infection of worms was used as the source of faeces containing worm eggs for the study. Culture of these eggs in the faeces showed that most of the worms were cyathostomes (small strongyles) with less than 1% large strongyles.
Control faeces were collected, before the horse was fed the fungus. The Duddingtonia flagrans was then fed to the horse at the rate 10 6 chlamydospores / kg body weight / day on four consecutive days. Faeces were then collected after the third day of fungal administration.
Ten 1kg faecal pats, five with the fungus and five without, were each placed on small square plots of pasture. This procedure was done three times during the summer in June, July and August. Samples of the surrounding herbage were taken every two weeks for two months to detect worm larvae migrating out of the faeces onto the herbage. The worm larvae collected from each plot were counted and identified.
On average, pasture surrounding faecal pats containing Duddingtonia flagrans had 94.8% fewer larvae.
It appears that the fungus has no detrimental effects on the degradation of horse faeces since it did not influence the rate at which the faeces were broken down. This suggests that the organisms involved in degrading the faecal pats, such as dung insects and earthworms, are not affected by the fungus. Despite this, the authors suggest that further investigations are required to assess the environmental effect of the massive use of the fungus that would occur if it were used continuously as a worm control measure.
These results show "that the use of nematode-trapping fungi against free-living larvae stages of horse strongyles represents a potentially useful method in equine parasite control" reports Dr Fernandez, one of the group. "Biological control would provide a significant contribution to the control of cyathostomes, and field experiments under different management conditions on stud farms should be conducted in the future."
For more details see:
A new isolate of the nematodophagous fungus Duddingstonia flagrans as biological control agent against free-living larvae of horse strongyles. A Silvina Fernandez, E Henningsen, M Larsen, P Nansen, J Gronvold, J Sondergaard. Equine Veterinary Journal (1999) 31 (6) 488-491.