In vitro evaluation of the efficacy of Duddingtonia flagrans using different doses of chlamydospores and different loads of gastrointestinal strongyle eggs in sheep feces

Nematophagous fungi represent an interesting biological alternative to conventional methods. Among the various species, Duddingtonia flagrans stands out for its ability to pass through the gastrointestinal tract unchanged. The number of chlamydospores required for the fungus to be effective in the presence of varying concentrations of gastrointestinal strongyle (GIS) eggs is largely unknown and remains a topic of discussion. The aim of this study was to evaluate, in vitro, the efficacy of D. flagrans in the faeces of naturally infected sheep by analyzing different concentrations of chlamydospores and varying levels of GIS egg counts. Fresh faeces from naturally infested sheep were collected in a farm in Central Italy. Based on fecal egg count, three batches of 150, 450 and 900 eggs per gram of feces (upg) were prepared. Each batch was divided into five groups. Four groups were inoculated with 1 ml of D. flagrans chlamydospore suspension containing 1000, 3000, 6250 or 11000 chlamydospores per gram (cpg), respectively. The fifth group served as a control, receiving 1 ml of distilled water. The cultures were incubated for 14 days at 24 degrees C. Each test was repeated three times for each group. Infecting larvae (L3) were recovered, counted and morphologically identified. The efficacy of D. flagrans, increasing with higher concentration of chlamydospore, ranging from 49.35 to 84.25% in the 150 epg groups; 40.97% to 87.47% in the 450 epg groups and 38.03% to 70,87% in the 900 epg groups. For all epg levels, the Kruskall-Wallis test showed significant differences (p-value <0.05), indicating that at least one treatment group had significantly different reduction of larvae compared to the others. Based on these results, D. flagrans appears to require a minimum concentration of chlamydospores in the faeces to exert a significant larvicidal effect. Conversely, the number of GIS eggs in the feces does not appear to be a determining factor for the fungal efficacy.