Information concerning whether fowl such as duck is a suitable reservoir host of Metagonimus yokogawai is largely unclear to date. In the present study, the growth and development of M. yokogawai metacercaria (Mc) in domestic duck (Cairina moschata) was determined by worm recovery rate (WRR) and morphological changes e.g., the size of fluke's body as well as their internal organs was assessed by using Semichon's acetocarmine staining. Each duck was orally inoculated with 50 Mcs of M. yokogawai and infected ducks were deeply anesthetized with ether and killed at 1, 2, 3, 4, 5, 6, 7, and 14 days post-infection (DPI). On each date, two infected ducks were killed and the small intestines of each duck were separated into four parts then they were opened longitudinally to harvest the flukes. Results revealed that WRR of M. yokogawai from inoculated ducks increased during early infection with a peak as seen at 4 DPI (28.5 ± 6.9%); thereafter it gradually decreased and a drastic decline was observed in 14 DPI (2.0 ± 1.1%) in the trial. The preference sites for M. yokogawai were low portions of the small intestine; nevertheless the size of fluke's body and organs developed increasingly with time and they maturated to produce ova from 4 DPI onward in the trial. However, present results indicated that ducks, based on the findings of this study, are not suitable hosts for establishment of M. yokogawai infection because most flukes were expelled from duck's intestine within 14 days. Nevertheless, it was proposed that ducks might play a certain role in transmitting M. yokogawai when they deposited the ova via feces into marsh where snails and fish were abundant since they could presumably establish transient and possibly patent infections with this parasite.
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