Schistosoma japonicum infection in the pig: the effect of a patent primary infection on a challenge infection

The response of pigs to a challenge infection of Schistosoma japonicum following a primary infection was assessed using parasitological parameters and eosinophil counts. Twenty-five Danish Landrace/Yorkshire/Duroc crossbred pigs were divided into four groups. Group A (n=10) received a primary infection, group B (n=5) received both a primary and challenge infection, group C (n=5) received a challenge control infection and group D (n=5) received no infection serving as helminth-free controls. A dose of 850 cercariae was administered by intramuscular injection at the primary infection (week 0) and challenge infection (week 12). The pigs were perfused at week 21, except for half of the group A pigs which were slaughtered at week 12. Challenge infection did not result in higher worm burdens or tissue egg counts in group B than group A at week 21 and mature/immature worm ratios were similar for the two groups. In addition, no increases in faecal egg counts or eosinophil counts were observed in group B after challenge infection. The results indicate that pigs are able to mount a very rapid and effective response to reinfection with S. japonicum following a patent primary infection resulting in prevention of establishment of challenge infection schistosomes. An anti-worm effect appears to be the main feature of this regulatory host response.