Lucía Emilia Iglesias

Hongos nematófagos utilizados para el control biológico de nematodos gastrointestinales en el ganado y sus formas de administración

The control of gastrointestinal nematodes relies at present mostly on antihelmintic treatments using synthetic molecules. This approach, however, has led to the appearance of resistance to some types of antihelmintics which, together with the need to cut down on the use of chemicals, has fostered the development of other control methods, such as biological control, which is the use of living organisms that are naturally antagonistic to an unwanted species. Among the natural enemies of nematode parasitic larvae is the microfungus Duddingtonia flagrans. Research has shown the ability of this fungus to reduce the number of nematode larvae in faeces, the ability of its chlamydospores to survive the passage through the gastrointestinal tract of livestock and, moreover, to keep its germinative ability, thus facilitating the development of formulations. The present review looks at the species currently used and the different ways of administering already tested nematophagous fungi.

Nematophagous fungi from decomposing cattle faeces in Argentina

BACKGROUND Biological control of gastrointestinal nematodes of ruminants by use of nematophagous fungi would become part of any livestock parasite integral control system. Identifying autochthonous species that could then be selected for mass production is an important phase in the practical use of biological control. AIMS To search for nematophagous fungi with potential use as biological control agents against gastrointestinal nematodes in Argentina. METHODS Decomposing cattle faeces sampled in different locations were incubated in water agar 2% with Panagrellus sp. The developed nematophagous fungi were transferred to new water agar 2% plates and then to corn meal agar plates in order to carry out their identification. Fungal diversity and richness were also assessed. RESULTS Seventeen species from nine genera of nematophagous fungi were found. Twelve species were nematode-trapping fungi and three species plus two fungi identified to genus level corresponded to endoparasitic fungi. Arthrobotrys conoides, Arthrobotrys oligospora, Duddingtonia flagrans, Monacrosporium doedycoides, Arthrobotrys robusta and Drechmeria coniospora were the most frequently isolated species overall in the whole study (6.6%, 5.7%, 5.7%, 5.7%, 4.7% and 4.7%, respectively) although other species were more frequently recorded at local levels such as Arthrobotrys pyriformis (18.8%). Only A. conoides has been previously isolated from ruminant faecal samples in Argentina. Five nematode-trapping fungal species are mentioned for the first time in the Americas CONCLUSIONS D. flagrans and A. conoides, both identified in the present study, are among the most promising ones as biological control agents against gastrointestinal nematodes of ruminants.

Lack of negative effects of the biological control agent Duddingtonia flagrans on soil nematodes and other nematophagous fungi.

The possible environmental effects of the massive use of Duddingtonia flagrans for controlling sheep nematodes were evaluated in two regions. Non-supplemented faeces and faeces from sheep supplemented with D. flagrans were deposited three times on pasture plots and samples were collected 7 and 14 days post-deposition. Samples were cultured in agar-water (2%) with Panagrellus spp. to recover D. flagrans and other nematophagous fungi, and soil nematodes were extracted using Baermann funnels and counted. No significant differences in the populations of soil nematodes and fungi colonizing sheep faeces (P > 0.05) were observed between supplemented and non-supplemented groups, except in one sample. The topsoil in contact with the faeces was sampled 1-4 months post-deposition, revealing that, with one exception, D. flagrans did not persist in soil beyond 2 months post-deposition. Duddingtonia flagrans does not affect faecal colonization by other fungi and soil nematodes and, once deployed on pasture, does not survive for long periods in the environment.

Predatory effect of Duddingtonia flagrans on infective larvae of gastro-intestinal parasites under sunny and shaded conditions

Duddingtonia flagrans is a natural strain of Nematophagous-Fungi isolated around the world. It has demonstrated efficacy and ease of use in laboratory as well as in field conditions. The fungus contributes to the prophylactic control of the worms by reducing the number of L3 on pasture. The aims of this study were to test and analyze the predatory effect of D. flagrans under sunny and shaded conditions on the L3 in the faeces, and to verify the reduction of translation to pasture during summer and winter seasons. Faecal Mass Units (FMUs) were assigned to two treated groups (groups treated with D. flagrans chlamydospores, TG) and two untreated groups (without D. flagrans chlamydospores, UG), in summer and winter, under sunny and shaded conditions. FMUs and herbage samples were taken for parasitological workup. Predatory activity of D. flagrans was evident under both conditions for the summer experiment but was not manifest for the winter experiment. In summer, an interaction between sunny and shaded conditions and predatory activity of D. flagrans was found. Environmental conditions on predatory activity should be considered when designing strategies for the implementation of D. flagrans in grazing systems to smooth the infectivity curve of L3.

Ivermectin dissipation and movement from feces to soil under field conditions

ABSTRACT 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 use of soy protein polymers as a release device for nematophagous fungi in the control of parasitic nematodes in ruminants

This trial was conducted to evaluate the predatory activity of Duddingtonia flagrans incorporated into soy protein-based polymers as a controlled-release device (CRD). The rate of fungal release from the polymers and time of residence of the CRD in the rumen of a cannulated sheep was also determined. After administration to the sheep, the CRD was extracted at weekly intervals over a month for observation of its physical structure and faeces were collected to observe the subsequent predatory activity of the fungus in Petri dishes with water-agar 2% and Panagrellus spp. as bait. The CRD slowly degraded in the rumen over 4 weeks and liberated D. flagrans into the faeces. The formulation of the soy protein-based polymers did not affect the predatory activity of the fungus. The study demonstrates that biodegradable soy protein polymers could potentially improve the use of nematophagous fungi for controlling nematode parasites of ruminants.