Trapping Behaviour of Duddingtonia flagrans against Gastrointestinal Nematodes of Cattle under Year-Round Grazing Conditions.

The purpose of using nematophagous fungi as biological control agents of gastrointestinal nematodes of livestock is to reduce the build-up of infective larvae on pasture and thus avoid clinical and subclinical disease. As the interaction of fungus-larval stages takes place in the environment, it is crucial to know how useful the fungal agents are throughout the seasons in areas where livestock graze all year-round. This study was designed to determine the predatory ability of the nematophagous fungus Duddingtonia flagrans against gastrointestinal nematodes of cattle during four experiments set up in different seasons. In each experiment, faeces containing eggs of gastrointestinal nematodes were mixed with 11,000 chlamydospores/g and deposited on pasture plots. A comparison between fungal-added faeces and control faeces without fungus were made with regard to pasture infectivity, larval presence in faecal pats, faecal cultures, faecal pat weight, and temperature inside the faecal mass. In three of the four experiments, Duddingtonia flagrans significantly reduced the population of infective larvae in cultures (68 to 97%), on herbage (80 to 100%), and inside the faecal pats (70 to 95%). The study demonstrated the possibility of counting on a biological control tool throughout most of the year in cattle regions with extensive grazing seasons.

A review of the use of Duddingtonia flagrans as a biological controller of strongylid nematodes in horses.

In horses, the nematodes of the Strongylidae family are the most important due to their prevalence and pathogenicity. Sanitary plans include parasite control based on chemical anthelmintics. Among these, the benzimidazole compounds have been used since the 1960s to control the nematode Strongylus vulgaris. Its inappropriate use resulted in the development of resistance in parasites with a shorter biological cycle, such as the small strongyles. Currently, the genera that make up this group show widespread resistance to all chemical treatments available in veterinary medicine, except for macrocyclic lactones, where less effective action has been detected. The need to find alternative routes for its control is recognized. International organizations and markets are increasingly restrictive in the allowed levels of drugs in products of animal origin, so one of the drawbacks is the permanence of chemical compounds in tissues. Therefore, other tools not chemically based are proposed, such as the biological control of gastrointestinal nematodes. Various research groups around the world have carried out tests on the control capacity of the nematophagous fungus Duddingtonia flagrans against this group of parasites. The objective of this review is to compile the different tests that are available on biological control in this species, in in vivo and in vitro tests, and the possible incorporation of this tool as an alternative method of antiparasitic control in an integrated control scheme of parasites.

In vitro efficacy of different concentrations of Duddingtonia flagrans on varying egg densities of gastrointestinal nematodes of cattle.

The nematophagous fungus Duddingtonia flagrans, used for the biological control of gastrointestinal nematodes in livestock, is fed to infected animals so its chlamydospores and the parasite eggs are voided together with faeces where the fungus preys on nematode larvae, thus reducing pasture infectivity. The number of chlamydospores needed for the fungus to be efficient in the presence of a wide range in numbers of parasitic eggs is largely unknown and a matter of discussion. The aim of this study was to determine the fungal efficacy of four different chlamydospore concentrations against three different levels of cattle faecal egg counts. Fungal concentrations of 11000, 6250, 3000 and 1000 chlamydospores/gram of faeces (cpg) were added to cultures containing 840, 480 or 100 eggs/gram of faeces (epg). After 14 days of incubation, the efficacy of D. flagrans, in decreasing order of chlamydospore concentrations, ranged from 100% (P < 0.0001) to 77% (P > 0.0999) in the 100 epg groups; 100% (P < 0.0001) to 92% (P = 0.4625) in the 480 epg groups and 100% (P < 0.0001) to 96% (P = 0.7081) in the 840 epg groups. The results indicate that the numbers of eggs in cattle faeces were not a determining factor on the fungal efficacy against gastrointestinal nematodes.

Ivermectin dissipation and movement from feces to soil under field conditions.

The aim of this work was to evaluate the fate of ivermectin (IVM) at two concentrations in cattle feces and its movement to the nearby soil and plants. Feces were spiked with IVM at two levels: 3000 ng g-1 (high group, HG) and 300 ng g-1 (low group, LG). Artificial dung pats were prepared and deposited in an experimental field area. Feces and underlying soil were sampled up to 60 days post-deposition (dpd). As an additional analysis, grasses growing around the pats were sampled at 30 and 60 dpd. Ivermectin concentrations in all matrices were determined by HPLC. Mean IVM fecal concentrations were in the range between 3901.9 ng g-1 and 2419.2 ng g-1 (high group) and 375.3 ng g-1 and 177.49 ng g-1 (low group). Mean times for 50% and 90% dissipation were 88.23 and 293.03 days (HG) and 39.1 and 129.9 days (LG). Soil concentrations ranged from 26.1 ng g-1 to 71.1 ng g-1 (HG) and 3.4 to 5.9 ng g-1 (LG); in plants, concentrations were between 71.4 and 380.8 ng g-1 and 5.40 and 51.8 ng g-1 in HG and LG, respectively. These results confirm that IVM moves from feces to the underlying soil as well as to nearby plants. The potential risk of detrimental effects on soil organisms and the impact on herbivorous animals should be further evaluated.

The route of administration drastically affects ivermectin activity against small strongyles in horses.

The goal of the current study was to evaluate the comparative efficacy of ivermectin (IVM) against small strongyles (cyathostomins) following its oral and intramuscular (IM) administration, in naturally parasitized horses. The parasitological data were complemented with the assessment of the plasma disposition kinetics of IVM. The trial included two different experiments. In experiment I, 40 horses naturally infected with small strongyles were randomly allocated into four experimental groups (n=10) and treated with IVM (0.2mg/kg) as follows: IVM oral paste, animals were orally treated with Eqvalan® (IVM 1.87% paste, as the reference formulation) by the oral route; IVM oral solution, animals were orally treated with Remonta® (IVM 2% solution, as a test formulation); IVM IM solution, animals were IM treated with the test product (Remonta® IVM 2% solution); and control, animals were kept without treatment as untreated controls. In experiment II, 24 horses naturally parasitized with small strongyles were randomly allocated into the same four experimental groups (n=6) described for experiment I. Faecal samples were individually collected directly from the rectum of each horse prior (day -1) and at 7 and 15 (Experiment I) or 7, 15 and 21 (Experiment II) days after-treatment, to assess the eggs per gram (epg) counts and estimate the efficacy of the treatments. Additionally, the comparative plasma disposition kinetics of IVM in treated animals was assessed in experiment II. In both experiments, an excellent (100%) IVM efficacy was observed after its oral administration (test and reference formulations). However, the IM administration of IVM resulted in a low efficacy (36-64%). Similar IVM plasma concentration was observed after its oral administration as a paste or as a solution. The higher IVM plasma profiles observed after the IM administration accounted for an enhanced systemic availability. The improved IVM efficacy observed against adult cyathostomins after its oral administration can be explained by an enhanced drug exposure of the worms located at the lumen of the large intestine. These findings may have a direct impact on the practical use of macrocyclic lactones in horses.