Acquired resistance to Opisthorchis viverrini in the hamster

Abstract
Two groups of ten hamsters received a primary challenge of five Opisthorchis viverrini metacercariae intragastrically (Groups I and III) and a third group was left untreated (Group II). 90 days after the primary challenge Groups I and II were given a further 50 metacercariae. Animals were killed 35 days after the secondary challenge and worm burdens and faecal egg counts evaluated. Compared with Group II animals, Group I showed a 24·88% reduction in mean liver worm burden, a diffeence which was significant at a level of P < 0·01 Differences for faecal egg output/worm between Groups I and II were not significant. This is the first effective demonstration of a degree of acquired resistance to O. viverrini and the possible relevance of these findings to the disease in man is discussed.