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.

El grado de antagonismo ejercido por los hongos sobre el desarrollo de los geohelmintos depende de la especie fúngica y las alteraciones morfológicas que causan. Los hongos saprofitos pueden tener efecto ovicida u ovistático sobre los huevos. El objetivo fue aplicar la microscopía electrónica de barrido (MEB) para observar la acción de 2 especies de Chrysosporium (C. indicum y C. keratinophylum) saprofitas de suelos, sobre huevos de Toxocara canis.Las especies a ensayar se sembraron en agar agua al 2% con una suspensión de huevos no embri-onados de T. canis y se incubaron 28 días a 28 °C. Como grupo control se utilizó una suspensión de huevos de T. canis en agar agua al 2%. El ensayo se realizó por triplicado para cada hongo y el grupo control. Las observaciones con MEB se realizaron a los 4, 7, 14, 21 y 28 días de incubación. La acción de los hongos se evaluó según las alteraciones en la superficie y los cambios en las características normales de los huevos. En este ensayo se observaron: hifas rodeando los huevos, appresorios penetrando la cubierta y cambios en la membrana característica del huevo, prevaleciendo el efecto tipo 3 (alteraciones que se producen tanto en el embrión como en la cubierta y penetración de hifas al interior de los huevos). La aplicación de la MEB permitió observar claramente que las 2 especies de Chrysosporium saprofitas de suelos, afectan el normal desarrollo de los huevos de T. canis, alteran su estructura y las alteraciones aumentan con el tiempo de exposición.

The aim of this work was to evaluate a dot-enzyme-linked immunosorbent assay (dot-ELISA) using excretory-secretory antigens from the larval stages of Toxocara canis for the diagnosis of toxocariasis. A secondary aim was to establish the optimal conditions for its use in an area with a high prevalence of human T. canis infection. The dot-ELISA test was standardised using different concentrations of the antigen fixed on nitrocellulose paper strips and increasing dilutions of the serum and conjugate. Both the dot-ELISA and standard ELISA methods were tested in parallel with the same batch of sera from controls and from individuals living in the problem area. The best results were obtained with 1.33 µg/mL of antigen, dilutions of 1/80 for the samples and controls and a dilution of 1/5,000 for the anti-human IgG-peroxidase conjugate. All steps of the procedure were performed at room temperature. The coincidence between ELISA and dot-ELISA was 85% and the kappa index was 0.72. The dot-ELISA test described here is rapid, easy to perform and does not require expensive equipment. Thus, this test is suitable for the serological diagnosis of human T. canis infection in field surveys and in the primary health care centres of endemic regions.