O ciclo evolutivo de Postharmostomum gallinum Witenberg, 1923, no estado do Rio de Janeiro, Brasil

Abstract

Terrestrial snails, Bradybaena similaris, Subulina octona, Leptinaria lamellata and Bulimulus tenuissimus, were found naturally infected with larval forms of a brachylaemid trematode in Rio de Janeiro State, Brazil. In preliminary studies, these infected snails were administered to domestic chickens (Gallus gallus), and adult trematodes were recovered from the intestinal caeca. The adult worms were found to belong to the species Postharmostomum gallinum Witenberg, 1923. This discovery made it possible to study the life cycle of this species in Brazil in order to find out which snails are more important in the local dissemination of the p a r a s i t e . The life cycle of P. gallinum and the morphology of the larval stages were found to be similar to those reported by Alicata (1940) for the same species in Hawaii, U.S.A. .47. Terrestrial snails serve as both first and second intermediate hosts, and infection of the avian definitive host results from the ingestion of the second intermediate host containing developed metacercariae. The same species of snails, that were found infected in nature, were exposed to eggs and cercariae of the parasite. It was found that only Bradybaena could be infected by both. Also, sporocysts were only found in that genus. It was shown that cercariae can pass from infected to uninfected snails and there grow to metacercariae. Thus, Bradybaena was shown to serve as both first and second intermediate hosts for P. gallinum. Subulina, Leptinaria and Bulimulus could not be infected by exposure to parasite eggs, but each of these genera developed metacercariae after being placed near infected Bradybaena under wet or humid conditions. This fact indicated that these three genera could serve as second intermediate hosts for the trematode. Chickens given either naturally or experimentally infected snails showed a pre-patent period of 24 to 27 days. It was also found to be possible, but difficult, to infect chickens with metacercariae isolated from snails. Attempts to infect ducks and pigeons with P. gallinum were unsuccessful. This study represents the first life cycle study reported for any brachylaemid trematode in Brazil, and .48. Leptinaria and Bulimulus are reported for the first time as potential second intermediate hosts for P. gallinum.