Soil fungi enable the control of gastrointestinal nematodes in wild bovidae captive in a zoological park: a 4-year trial

Nematophagous fungi as biological control agents of parasitic nematodes in soils of wildlife parks

Infections with soil-transmitted helminths pose a significant threat to wildlife in enclosures, where transmission of these parasitic larvae is easier due to the limited space. Nematophagous fungi offer a promising solution as they can naturally control these nematodes. In this study, three nematophagous fungi (Arthrobotrys oligospora, Dactylaria scaphoides, Nematoctonus leiosporus) purchased from the non-profit global biological resource center ATCC were tested for their suitability as biological control agents. The nematodes Strongyloides sp., Trichostrongylus sp. and Oesophagostomum sp. Were isolated from three animal species: wild boar (Sus scrofa) (n = 10), fallow deer (Dama) (n = 5) and mouflon (Ovis orientalis musimon) (n = 5) from a wildlife park using the Baermann-Wetzel method. In a second step, the fungi were brought into contact with the parasites on the soil of the enclosures. The two media tests showed that the nematophagous fungi were more effective on the agar plate than on the autoclaved soil. Only D. scaphoides showed good efficacy on both media, while the other two fungi showed more marked differences on the two media. The results showed that these three nematophagous fungi can reduce parasites in soil before they are ingested by an infected animal. Given the increasing development of drug resistance and the use of chemical agents for soil treatment, this is an important finding that should be pursued in the future.

Formulating Parasiticidal Fungi in Dried Edible Gelatins to Reduce the Risk of Infection by Trichuris sp. among Continuous Grazing Bison

Control of infection by gastrointestinal nematodes remains a big problem in ruminants under continuous grazing. For the purpose of decreasing the risk of infection by Trichuris sp. in captive bison (Bison bison) always maintained in the same plot, dried gelatins having ≥106 chlamydospores of both Mucor circinelloides and Duddingtonia flagrans were given to them for one week, and at the end, fecal samples (FF) collected each week for four weeks were analyzed immediately. Feces taken one week prior to gelatin administration served as controls (CF). Eggs of Trichuris sp. were sorted into non-viable and viable, then classified into viable undeveloped (VU), viable with cellular development (VCD), or viable infective (VI). Ovistatic and ovicidal effects were determined throughout the study. In FF, viability of Trichuris eggs decreased between 9% (first week) and 57% (fourth week), egg development was delayed during the first two weeks, and VI percentages were significantly lower than in CF (p = 0.001). It is concluded that the preparation of gelatins with chlamydospores of parasiticidal fungi and their subsequent dehydration offer an edible formulation that is ready to use, stress-free to supply, and easy to store, as well as being well-accepted by ruminants and highly efficient to reduce the risk of Trichuris sp. infection among animals under continuous grazing regimes.

A New Comestible Formulation of Parasiticide Fungi to Reduce the Risk of Soil-Transmitted Helminth Infections in a Canine Shelter

Dogs cared for in a shelter are dewormed every three-four months, but they all become infected one-two months later by the soil-transmitted helminths (STHs) Toxocara canis, Toxascaris leonina, Trichuris vulpis, and Ancylostoma caninum. For the purpose of reducing their risk of infection by decreasing the survival of helminths' infective stages in soil, chlamydospores of two parasiticide fungi, Mucor circinelloides (ovicide) and Duddingtonia flagrans (larvicide) were formulated as handmade edible gelatins and given three days per week for 17 months to 18 dogs (DRF, dogs receiving fungi); a second group was maintained without fungi (CD, control dogs). All individuals were dewormed at months 0, 3, 7, 10 and 13, and it was observed that the levels of helminths egg-output were reduced by 96-98% fourteen days after each treatment. Fecal egg counts of STHs were similar in both groups until the 6th-8th months, and then remained significantly lower in DRF than in CD (42-100% ascarids; 30-100% trichurids and ancylostomatids). According to the results, and considering that gelatin treats have always been fully accepted, it is concluded that this new formulation offers an efficient solution to decrease the risk of infection among dogs maintained in shelters, and is therefore recommended.

Are Anthelminthic Treatments of Captive Ruminants Necessary?

Anthelmintics are frequently administered to animals to limit fecal egg elimination, so that wild animals in captive breeding programs are treated to maintain a proper health condition. This is effective from a health management perspective, but on the other hand, it could prevent captive animals from developing an effective immunity against parasites that they might encounter when reintroduced into their original geographic areas. The aim of this study was to describe the dynamics of parasite infections in captive Cuvier’s gazelles (Gazella cuvieri) not treated with anthelmintics for two years and to evaluate the factors related to their fecal egg shedding. Fifteen one-year-old males were enclosed together and captured monthly to collect feces directly from the rectum. Fecal egg counts were performed, and eggs were classified as strongylid-like, Nematodirus sp., or Trichuris sp. Fecal egg shedding for the three groups of parasites did not vary significantly over the duration of the study. Only precipitation affected the egg-shedding pattern of all parasites, while inbreeding was positively associated with the number of strongylid-like parasites. These findings suggest an equilibrium between hosts and parasites in absence of treatment during the study. The anthelmintic treatment as a systematic prophylaxis method in captive animals should be avoided and replaced by systematic coprological and clinical vigilance, as well as targeted treatment in the case of a significant rise of fecal egg counts.

Control of Strongyles in First-Season Grazing Ewe Lambs by Integrating Deworming and Thrice-Weekly Administration of Parasiticidal Fungal Spores

Parasiticidal fungi have been used in several in vivo experiments in livestock farms worldwide, constituting an effective tool for the biocontrol of gastrointestinal parasites in grazing animals. In the first year of study, two groups of eight first-season pasturing ewe lambs infected by strongyles were dewormed with albendazole, and then, the test group received an oral dose of 10⁶ chlamydospores of Mucor circinelloides and 10⁶ Duddingtonia flagrans individually and thrice a week from mid-September to May (FS1), while the control group remained without fungi (CT1). In the second year, two new groups of first-season grazing ewe lambs were treated with ivermectin and subjected to the same experimental design (FS2 and CT2, respectively). The anthelmintic efficacy was 96.6% (CT1), 95.6% (FS1), 96.1% (CT2), and 95.1% (FS2). The counts of strongyle egg output increased in the control groups (CT1 and CT2) throughout the study and reached numbers higher than 600 eggs per gram of feces (EPG), while in FS1 and FS2, they were <250 EPG. The values of red blood cell parameters registered for CT1 and CT2 were lower than those of the reference standards, while a significant increment was recorded in FS1 and FS2, and values within the physiological range were attained. It is concluded that integrating efficient anthelminthic deworming with rotational pasturing and the regular intake of chlamydospores of M. circinelloides and D. flagrans provides a helpful strategy for maintaining low levels of strongyle egg output in first-season grazing ewe lambs and improves their health status.

The Control of Zoonotic Soil-Transmitted Helminthoses Using Saprophytic Fungi

Soil-transmitted helminths (STHs) are parasites transmitted through contact with soil contaminated with their infective eggs/larvae. People are infected by exposure to human-specific species or animal species (zoonotic agents). Fecal samples containing eggs of Ascaris suum or Lemurostrongylus sp. were sprayed with spores of the soil saprophytic filamentous fungi Clonostachys rosea (CR) and Trichoderma atrobrunneum (TA). The antagonistic effect was assessed by estimating the viability of eggs and their developmental rate. Compared to the controls (unexposed to fungi), the viability of the eggs of A. suum was halved in CR and decreased by two thirds in TA, while the viability of the eggs of Lemurostrongylus sp. was reduced by one quarter and one third in CR and TA treatments, respectively. The Soil Contamination Index (SCI), defined as the viable eggs that attained the infective stage, reached the highest percentages for A. suum in the controls after four weeks (66%), with 21% in CL and 11% in TA. For Lemurostrongylus sp., the values were 80%, 49%, and 41% for control, CR and TA treatments, respectively. We concluded that spreading spores of C. rosea or T. atrobrunneum directly onto the feces of animal species represents a sustainable approach under a One Health context to potentially reduce the risk of zoonotic STHs in humans.