Scarce and inconclusive information on general biological impact of Toxocara invasion on paratenic hosts, and people in particular, has led us to undertake a comprehensive study of the problem. The study has been conducted in a rural environment, which is considered a toxocarosis risk factor. In total 200 soil samples have been screened for Toxocara eggs by flotation, of which 14.5% were positive. Backyards close to households were most heavily contaminated with infectious eggs--21.7% of positive samples. ELISA serological tests performed on 242 lower-secondary students found 14.5% of the studied population to be definitely positive--16.5% of boys and 12.8% of girls, respectively. The odds of being infected with Toxocara were 2 times (CI: 1.15-3.85) more likely for individuals who owned a cat than those who did not own a cat. Strong significant correlation between seropositivity and the presence of a dog in a household was found with boys. The level of developmental age was significantly higher in seropositive than in seronegative students. No significant correlation has been observed between the motor abilities and seropositivity of students. Seropositive boys had significantly lower end-of-year grades than their seronegative counterparts.

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A polymerase chain reaction (PCR) technique has been used for the differentiation of T. canis and T. cati eggs isolated from soil and previously identified from microscopical observations. The method, using specific primers for the identification of the two Toxocara species, was assessed in both the field and laboratory. Successful results were obtained when only a single or large numbers of eggs were recovered from 40 g soil samples. The method is sensitive, allows analysis of material independent of the stage of egg development and can be adapted for the recovery of other species of parasites from soil.

The antiviral immunity of human placenta and amniotic membrane in an organ culture (OC) system was studied. Freshly isolated explants of most of the placentas at term and the amniotic membranes were found to be relatively resistant to herpes simplex virus type 1 (HSV-1), encephalomyocarditis virus (EMCV), and vesicular stomatitis virus (VSV) infections. After in vitro aging, however, the OC acquired the sensitivity to the viruses. In about 66%-90% of placentas, resistance of freshly isolated explants to the infection was observed. This indicates that the placentas displayed a constitutive immunity against the viruses. To study the role of endogenous cytokines in antiviral immunity, we added specific antibodies neutralizing IFN and TNF activities to VSV-infected OC and checked their influence on viral replication. Increases of 10-fold to 100-fold of VSV replication in the OC treated with anti-TNF-alpha, anti-IFN-alpha, anti-IFN-gamma or anti-IFN-beta sera were observed. The results indicate the importance of the endogenous cytokines in placental and amniotic membrane immunity. However, we did not observe a simple correlation between the spontaneous IFN and TNF production and the level of resistance against viruses. In view of the results, the participation of TNF and IFN in the constitutively expressed immunity of human placenta is of a more complex nature.

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