Growth and development of Massaliatrema misgurni (Trematoda: Heterophyidae) in mice and its metacercarial morphology.

The morphology of metacercariae of Massaliatrema misgurni Ohyama et al. (Ohyama et al., Parasitol Int 2001; 50; 267-71) was described, and their infectivity, egg output, growth and development in mice until day 35 post infection (PI) were studied. Metacercarial cysts from loaches imported from China to Japan were 199-349 microm in diameter and consisted of a very thick translucent outer layer and a refractile inner layer. Excysted metacercariae basically had the shape of miniature adults, and a pair of pre-developed testes but no other genital organs were recognized. The worm recovery rate from mice was 36.7-51.7% during days 3-7 PI, and decreased remarkably to 2.5 and 1.7% at days 28 and 35 PI. The prepatent period was 3-4 days, and the egg output quickly increased and sustained high levels at days 5-7 PI, then decreased suddenly at day 8 PI, and continued at a low level until day 28 PI. The size of the body and inner organs such as the oral sucker, pharynx, acetabulum, testes, ovary and seminal receptacle quickly increased until day 3 PI, and sustained at a plateau level until day 21 PI except testes which gradually decreased until 21 PI. The number of the uterine eggs increased with a short time lag compared to other genital organs and sustained a plateau level until day 21 PI. Compared with other Heterophyidae species, M. misgurni was characterized by the remarkably fast growth and development.