[Studies on the life cycle of Paragonimus heterotremus]

In order to clarify the biological features of the lung fluke, Paragonimus heterotremus, it is necessary to replicate its complete life cycle in the laboratory.

Tricula wumingensis infected with the miracidiae of P. heterotremus were regularly dissected after infection for larvae observation. The cercariae of P. heterotremus from positive snails were used for experimental infection of the crab, Samanniathelphusa nanningensis. The crabs were then examined for the metacercariae at regular intervals. The infection of mammals (cats and rats) was performed with the metacercariae obtained from experimentally infected crabs.

The miracidia were hatched by incubating the eggs in water (room temperature 20 degrees C to 31 degrees C) for 16 days to 21 days. The epidermal cells of the miracidia were arranged in 4 transverse rows, 6 in the first row, 7 in the second, 3 in the third, and a single terminal cell at the posterior end of the body. The cells of the first row have indentation in their bases. Mature sporocysts, first generation rediae and second generation rediae(containing dissociative cercariae), were found on the 26th day, 41st day and 58th day after infection of the snails respectively(room temperature 21 degrees C-30 degrees C). The sporocyst had a birth pore at its anterior tip. The length ratio of the gut to the body was 1:3 in the first and 1:6 in the second generation rediae. The mature second generation rediae contains 5-21 mature cercariae which emerge from its pharynx. The cercaria has general characteristics of Paragonimus. Its flame cell pattern was formulated as 2[(2 + 2 + 2) + (2 + 2 + 2)] = 24. After the infection of crabs with cercariae, the mature metacercariae were found in the crabs on the 60th day. The crabs could be successfully infected by either: giving mature cercariae orally to them or raising them in water with positive snails. After the metacercariae obtained from experimental crabs were given to cats and rats, P. heterotremus adult worms were recovered from the worm-cyst in their lungs. The morphology of various larval stages and adult worms were described.

The life cycle of P. heterotremus was completed for the first time in the laboratory. The whole life cycle from egg to adult worm has been described in the present study.