A second peak of egg excretion in Strongyloides ratti-infected rats: its origin and biological meaning.

In Strongyloides ratti-infected rats, 2 peaks of egg excretion were observed; a large one with maximum egg production on days 7-8 of infection and a small more inconspicuous one around day 25. The second peak, which had been ignored in most studies, was produced by adults in the caecum and the colon. The adults were larger in length and had more embryonated eggs in the uterus compared with adults in the small intestine at day 25 post-infection. It is suggested that parasitic adults once expelled from the small intestine resettle and recover in the large intestine. Filter paper faecal culture carried out for 9 days at different days post-infection revealed that the total number of infective larvae that developed during the second peak was twice the number that developed during the first peak, despite the fact that total egg output during the second peak was less than one twentieth of the first peak. The results suggest that the small second peak was as important as the first one in the transmission of S. ratti.