Drug-abbreviated infections of Trichostrongylus colubriformis and development of immunity in jirds (Meriones unguiculatus)

The objective of this study was to examine the development and the duration of immunity achieved with drug-abbreviated infections of Trichostrongylus colubriformis in jirds (Meriones unguiculatus). Jirds were primarily infect ed either by trickle infection with 6 x 100 infective larvae (L-3) Of T. co lubriformis at 3-day intervals or by a single infection with 600 L-3. On da y 35 postinfection, one batch of jirds from each group was autopsied; the o thers were treated with oxfendazole at a dose of 5 mg/kg and were challenge d with 1,000 L-3 On either day 7 or day 42 post-treatment. All jirds were a utopsied at 17 days post-challenge. Trickle infection resulted in lower lev els of egg production during the primary infection period. The systemic IgM and IgG antibody response was significantly stronger in trickle-and single -infected groups as compared with the negative control group (P < 0.01-P < 0.05). Significantly higher levels of intestinal IgA were demonstrated in t rickle- and single-infected groups than in the negative control group (P < 0.01). Numbers of mucosal mast cells increased following infection, but thi s was not dependent on the type of immunisation. After challenge the extent of worm reduction was greater in trickle-infected than in single-infected subgroups. The IgM and Ige response was significantly stronger in challenge d subgroups as compared with negative control subgroups (P < 0.01). However , the IgG response was weaker in control challenged subgroups than in chall enged subgroups (P < 0.01). There was a negative correlation between the Ig G response and the worm burden after the second challenge (r = -0.73). The acquired immunity to T. colubriformis infection in jirds developed within 5 weeks of primary infection. The level of immunity was higher after trickle infection than after single infection. Furthermore, the immunity persisted for at least 6 weeks after oxfendazole treatment in the absence of a worm burden and larval intake, which is very similar to the situation in domesti c ruminant hosts.