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 para meters and eosinophil counts. Twenty-five Danish Landrace/Yorkshire/Du roc crossbred pigs were divided into four groups. Group A (n = 10) rec eived a primary infection, group B (n = 5) received both a primary and challenge infection, group C (n = 5) received a challenge control inf ection and group D (n = 5) received no infection serving as helminth-f ree controls. A dose of 850 cercariae was administered by intramuscula r injection at the primary infection (week 0) and challenge infection (week 12). The pigs were perfused at week 21, except for half of the g roup A pigs which were slaughtered at week 12. Challenge infection did not result in higher worm burdens or tissue egg counts in group B tha n 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 eosi nophil counts were observed in group B after challenge infection. The results indicate that pigs are able to mount a very rapid and effectiv e response to reinfection with S. japonicum following a patent primary infection resulting in prevention of establishment of challenge infec tion schistosomes. An anti-worm effect appears to be the main feature of this regulatory host response. (C) 1997 Elsevier Science B.V.