In vivo development of Echinostoma malayanum Leiper, 1911 with notes on effects of population density, chemical composition and pathogenicity and in vitro excystment of the metacercaria (Trematoda: Echinostomatidae)

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Abstract
In vivo development of Echinostoma malayanum Leiper, 1911 was studied in white rats and the developmental process was arbitrarily divided into four stages: organogeny, vitellogenesis, formation of Mehlis' gland complex and cirrus sac, and oviposition. The percentage of development was 86–94. Population density affected the prepatent period of flukes and the normal prepatent period of 13–16 days was altered to 18–23 days in infection with 500–800 flukes. The majority of flukes in heavy infection were undersized and in the immature stage of development at patency. Data from chemical analysis of flukes revealed that protein, lipids, calcium and ash decreased quantitatively in flukes from higher population densities but no such change was observed as regards glycogen. Pathological changes in the rat intestine included lysis and destruction of mucosa, increased activity of goblet cells, oedematous and reticulated appearance of lamina propria and slight to moderate hyperplasia of epithelial cells. The metacercariae excysted in the medium containing trypsin plus sodium cholate and pepsin, though not essential for a high percentage of excystment, affected the rate. The reductant sodium dithionite substantially enhanced the rate and percentage of excystment. Excystation was optimal at pH 8, and 42° C was more effective than 39° C.