Human toxocariasis is a zoonosis caused by infection with larvae of the ascarid nematode Toxocara canis and, less frequently, T. cati. Our study developed a method for distinguishing distant from recent human toxocariasis by assessing the avidity of the IgG antibodies. The avidity of specific antibodies increases with time after antigen challenge and assessment of the degree of avidity can be used to discriminate between recent and distant infections. The relative avidity was measured in 150 sera from children with visceral toxocariasis and in 46 sera from children with ocular toxocariasis. The probable time of infection was estimated on the basis of the medical history and clinical syndrome. Our study showed that 94.2% of positive sera collected from patients reporting infection > 6 months ago had high IgG avidity values, confirming distant toxocariasis, whereas 25.9% of positive sera taken < 6 months after infection showed low indices of IgG avidity. Our results suggest that measurement of the specific IgG avidity may assist in discriminating between recent and distant toxocariasis. The method can be used effectively to rule out (because of high avidity) a recently acquired infection. Low avidity is less reliable in discriminating between recent and distant infections.

Faecal samples deriving from 391 animals belonging to nine species (polecats, badgers, martens, weasels, rats, dogs, cats, red foxes, raccoon-dogs) were examined by capture ELISA for the presence of the Echinococcus multilocularis coproantigen. The main claim of our studies is the reliable detection of E. multilocularis coproantigens, mainly in the faeces of foxes, dogs and cats. For the first time in coproantigen detection we used a "double-sandwich" ELISA. The main advantage of this method is the higher specificity and better differentiation of positive and negative faecal samples, in comparison with sandwich ELISA. The overall specificity of double-sandwich ELISA was 95.1% with only 16 of 327 E. multilocularis-free animals giving false-positive results. The E. multilocularis coproantigen was detected by double-sandwich ELISA in 37.5% of examined red foxes and in 8.0% of examined raccoon-dogs, compared with a prevalence of just 29.8% in red foxes and 8.0% in raccoon-dogs, as determined by parasitological techniques.

Trichinella spiralis larvae were examined in TEM to identify calcareous corpuscles in the outer part of parasite capsule. The microroentgenographic analysis of calcareous corpuscles mainly demonstrated the presence of phosphorus and calcium. The physiological importance of calcareous corpuscles, as well as their significance in decay of T. spiralis larvae were discussed.