In vitro effect of Chrysosporium indicum and Chrysosporium keratinophylum on Toxocara canis eggs

The degree of antagonism exercised by fungi on geohelminth development varies according to the morphological alterations caused by different fungal species. Saprophytic fungi may exert ovicidal or ovistatic effects. The aim of this study was to apply scanning electron microscopy (SEM) to observe the action of two soil saprophytic species of Chrysosporium (C. indicum and C. keratinophylum) on Toxocara canis eggs. The fungal strains to be tested were incubated for 28 days at 28°C in 2% water agar with a suspension of unembryonated T. canis eggs. A suspension of T. canis eggs in 2% water agar was used as control group. The assay was done in triplicate for each fungus and the control group. SEM observations were performed on the 4th, 7th, 14th, 21st, and 28th day after inoculation. The effect of the fungi on eggs was evaluated in accordance with the alterations observed on the surface and the changes in the normal characteristics of the eggs. Hyphae around the eggs, appresoria penetrating the shell and changes in the typical egg membrane were observed in this assay. Type 3 effect (alterations that occur both in the embryo and the shell, and hyphal penetration of the eggs) was the prevalent effect. SEM allowed us to observe clearly the morphological alterations in T. canis eggs due to the effect of C. indicum and C. keratinophylum. Both saprophytic species of Chrysosporium alter the egg structure and alterations increase as exposure increases.

Comparison of the effect of the chosen species of saprotrophic fungi on the development of Toxocara canis and Ascaris suum eggs

The study aim was to compare the antagonistic interaction between saprotrophic soil fungi and embryonic development of geohelminths Toxocara canis and Ascaris suum. The experimental cultures were fertilized eggs of T.canis and A. suum incubated together with mycelium of strains: Fusarium culmorum, Metarhizium anisopliae,Paecilomyces fumosoroseus, Trichoderma viride and Trichothecium roseum. In the control cultures the eggs of both nematode species were incubated without fungi. The experiment was conducted at temp. 26°C for 60 days. Compared with the control, all of the tested species of fungi significantly extended the embryonic development of both T. canis and A. suum. Most inhibitory effect on the rate of embryonic development of T. canis and A. suum had three fungal species: P. fumosoreus, M. anisopliae and T. viride. Compared with the control, on the 60th day of incubation in the presence of each of the tested fungal species, a larger percentage (p<0.05) of morphological abnormalities was stated in developing embryos of T. canis (49–69%) than in A. suum (15.1–67.7%). Among the examined fungal species, only incubation with P. fumosoroseus resulted in significantly greater (p<0.05) incidence of embryonic malformations(embryopathies) in T. canis, as compared with A. suum. Also the percentage of dead larvae of T. canis in the control and in cultures with fungi (12% and 100%, respectively) was significantly higher in comparison with A. suum (0.5% and 10.3–36%, respectively). The highest percentage of non-viable larvae of A. suum was found in the presence of P.fumosoroseus, and the lowest in the presence of M. anisopliae. Findings may indicate that T. canis eggs are more sensitive to antagonistic interaction of the examined fungal strains than A. suum eggs.

Hongos nematófagos de huevos de Toxocara canis en un paseo público de La Plata, Argentina

Fungi have showed a great potential for the biological control of nematodes. However, they have not been evaluated for the control of animal and/or human parasites transmitted by egg contaminated soils. Environmental contamination with Toxocara spp. eggs is a public health problem. Accidental swallowing of Toxocara canis eggs (a nematode of dogs) usually results on a zoonotic infection (toxocarosis). The objectives of this research were: 1) To test the presence of antagonistic fungi against T. canis in the soil in public places of La Plata city, Argentina, infected with eggs of this parasite, 2) To determine the possible association between biotic and abiotic factors of the soil with the presence of fungal parasites of egg nematodes. Soil samples were tested for: textural type, organic matter (%), pH, presence of egg-parasite fungi, of larvae and of nematode eggs, in particular of Toxocara spp. The studied area showed the following characteristics: pH: 6.6-8.0, organic matter: 1.2-70%, with a predominantly loam texture. The following antagonistic fungal genera were identified: Acremonium, Aspergillus, Chrysosporium, Fusarium, Humicola, Mortierella, Paecilomyces and Penicillium. A prevalence of 70% was detected for nematode eggs, of 33% for Toxocara spp. eggs and of 90% for larvae. No association between the presence of egg-parasite fungi and the considered factors was found. More studies are necessary to know the natural antagonism factors to T. canis eggs for its in situ biological control.

Biological interaction between soil fungi and Toxocara canis eggs

Fungi from the soil of public areas in La Plata, Argentina were isolated and evaluated for their biological interaction with Toxocara canis eggs in vitro. We isolated and identified two fungal species: Fusarium pallidoroseum and Mucor hiemalis. Each species was co-cultured with T. canis eggs in sterile distilled water. The samples were observed by light and scanning electron microscopy (SEM) at days 4, 7 and 14 post-inoculation. Under the conditions of our experiments, F. pallidoroseum exhibited a high ovicidal activity on T. canis eggs, whereas M. hiemalis exhibited no such effects.

Biological activity of Paecilomyces genus against Toxocara canis eggs

Saprophytic soil fungi can exert ovicidal and ovistatic effects on helminths with differing degrees of efficiency. The representatives of such fungi from temperate regions, Paecilomyces lilacinus (Thom) Samson and P. marquandii (Masse) Hughes, exhibit recognized ovicidal activity on some nematodes. We evaluated the action in vitro of P. lilacinus and P. marquandii on the zoonotic canine roundworm eggs of Toxocara canis. Eggs exposed and unexposed to fungal samples were observed by both light and scanning electron microscopy on days 4, 7 and 14 post-inoculation. Ovicidal activity of P. lilacinus on T. canis eggs was considered to be high and that of P. marquandii to be intermediate.