THE IMPACT OF PRIMARY SCHISTOSOMA-BOVIS INFECTION ON A SUBSEQUENT CHALLENGE INFECTION IN GOATS

Experimental primary and challenge Schistosoma bovis infections were s tudied in West African Dwarf goats, using clinicopathological and para sitological parameters. The experiment included 44 goats divided into 4 groups of which group A received primary infection, group B received primary and challenge infection, group C received a challenge control infection, and group D included noninfected controls. Primary infecti on (wk 0) and challenge infection (wk 16) both comprised exposure to 1 ,000 cercariae per goat, and necropsies took place 16, 22, and 32 wk f ollowing primary infection. Clinicopathological effects were moderate in all infected groups. Egg excretion became gradually reduced followi ng peak levels during early primary infection, and egg excretion incre ased only marginally following challenge infection in the primary- and challenge-infection group. Similarly, challenge infection of primary- infected goats did not result in an increase ih tissue egg counts. Wor m recovery and tissue egg counts in primary-infected goats remained co mparable throughout the experiment, and although evidence was obtained for a delay in maturation, challenge worm establishment was comparabl e with challenge-control worm establishment. An anti-fecundity effect is thus an essential component of the regulatory response to both prim ary and challenge S. bovis infection in the goats. However, it was als o shown that the intrauterine egg count is an unreliable parameter for fecundity assessments.