The effects of exposure of juvenile Lymnaea stagnalis to one, two or, four miracidia of Trichobilharzia ocellata on the following parameters were studied: infection rate, length of prepatent period, production of cercariae, growth and ovipository activity of the snails, and the weights of their accessory sex organs. An infection rate of 100% was established with all miracidial doses. Morality of the snails was low in all experimental groups. In cercarial production high-(HP) and low-productive (LP) infections could be distinguished. An increase in miracidial dose at exposure results in an increase in the number of snails with HP-infections and decreases the length of the prepatent period of these infections. Snails with HP-infections grow faster than controls after day 14 post-exposure and show giant growth, while the accessory sex organs remain very small. The snails show hardly any ovipository activity. In all snails with HP-infections these effects are observed independent of the miracidial dose at exposure. Snails with LP-infections demonstrate no signs of gigantism, their accessory sex organs are almost identical to those of controls, and the snails show ovipository activity. It is concluded that the occurrence of HP- and LP-infections indicates differences in reproductive capacity of the parasite. HP-infections can only develop when the parasites can adjust the host to their requirements at an early stage of the infection.

The effect of intratracheal surfactant instillation on pulmonary function in rats with Pneumocystis carinii pneumonia (PCP) was investigated. In those animals which developed PCP with severe respiratory failure after administration of cortisone acetate s.c. over 8-12 weeks, pulmonary function was improved by surfactant instillation. PaO2 values 30 min after surfactant instillation were significantly higher compared to pretreatment values and also compared to PaO2 values of rats 30 min after receiving saline (482.9 mmHg +/- 44.7, 170.7 mmHg +/- 39.3 and 67.2 mmHg +/- 17.4, respectively). Histological examination showed that alveoli of rats with PCP which received no exogenous surfactant are filled with foamy edema, whereas after exogenous surfactant alveoli are stabilized and well-aerated. These results indicate that exogenous surfactant may help patients with severe PCP to overcome an acute stage of respiratory distress.

Juvenile specimens of Lymnaea stagnalis were exposed to 0 or 4 miracidia of Trichobilharzia ocellata. Highly productive infections developed in all infected snails. Qualitative and/or quantitative light microscopic observations were performed at various intervals between day 0 and 83 post exposure (p.e.). Gonadal maturation started between day 4 and 7 p.e. in all snails, but in infected animals gonadal growth was retarded considerably after day 7 and was blocked from day 19 onwards. This resulted in very small gonads (10% of the volumes of those of controls on day 83 p.e.) in infected snails, in which however, gametogenesis was initially normal. Due to the small gonad volume gamete production was highly reduced. From day 33 onwards spermatogenesis appeared to be inhibited and around day 83 oocyte maturation seemed to be impaired. The accessory sex organs (ASO) of infected snails showed a similar reduced growth. The cellular differentiation and production of secretory granules in these small ASO was normal albeit delayed in both the male and female organs. The severe reduction in growth of the gonad and the ASO started in the presence of immature primary sporocysts, the later effects on gametogenesis were simultaneous with the production of massive numbers of cercariae. These results are discussed in view of the available data on the endocrine control or reproduction in L. stagnalis. It is suggested that either the secretion of gonadotrophic hormones or the response of their targets is reduced by humoral effects of the parasites.

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