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Serum antibody responses to infection with the intestinal helminth Trichinella spiralis in mice remain at low levels for the first ten to 12 days, slowly increasing to high titres around day 20. It is thought that antibody, therefore, has a limited role in the primary immune response raised against this infection and this is confirmed by the inability of primary infection serum to transfer immunity adoptively. High-responder NIH and low-responder B10 mice were vaccinated with T.spiralis antigen in Freund's complete adjuvant prior to challenge. This procedure conferred significant protection on NIH mice but not B10. Sera from these mice were transferred into recipients before and during challenge infection. Significant levels of protection were obtained in both strains with both homologous and heterologous sera, even though vaccination itself had not resulted in protection of the B10 donor mice. These data indicate that the B10 strain is potentially capable of making a protective immune response against the intestinal phase of T.spiralis.

Levels of intestinal nematode infections were assessed six months after a two year trial of ivermectin for efficacy against onchocerciasis had ended. In the trial the inhabitants of six villages in Sierra Leone were offered treatment with ivermectin or placebo at six monthly intervals for four rounds in total. Quantitative faecal egg counts were carried out on stool samples provided by 202 subjects, all of whom had received all four rounds of treatment, in two of the villages (Dodo and Mogibisi). These data were analysed by a novel procedure in which a 3-way ANOVA with negative binomial errors enabled village and host gender influences on the outcome of treatment to be identified. Necator americanus was the most common species showing an overall prevalence of 90% but a higher intensity in Mogibisi relative to Dodo, particularly among male subjects. Neither prevalence nor intensity of infection were altered in ivermectin-treated compared with placebo-treated subjects. Trichuris trichiura was the least common species with a prevalence of 15%. It was concluded that there was no significant protection from infection with this species among the ivermectin relative to the placebo-treated subjects. Ascaris lumbricoides, with an overall prevalence of 39%, was more common among female (50%) compared with male (27%) villagers. Prevalence was not significantly affected by ivermectin but the intensity of infection declined by 91.3% in Dodo whilst in Mogibisi intensity was only reduced by 14.6%. The results indicate that the long-term benefits of treatment of necatoriasis and trichuriasis with ivermectin are likely to be minimal whilst those of ascariasis will depend on the individual characteristics of local communities and may differ quite markedly within a limited geographical area. Possible explanations for the discrepancy in efficacy between villages are considered.

cause all lanes contained antigens of epimastigotes that could be contaminated with antigens of the medium used to grow these organisms a further control was performed in which lanes with epimastigote medium were reacted with each of the antisera employed. No bands were noted in this control. These results are of interest particularly when the 90and 72-kd antigens are considered. The observation that the 90-kd antigen has been shown to be protective (Snary, 1983, loc. cit.), and our results, which reveal that antibodies to this antigen were present in the sera of rabbits injected with live epimastigotes and absent in sera of rabbits immunized with formalin-killed organisms of this stage, suggest that the antigen was apparently inactivated or destroyed by formalinization or was in such low concentration that it did not induce a sufficient antibody response. This might explain why immunization with formalin-killed organisms is far less effective in inducing resistance than immunization with live organisms (Brener, 1980, loc. cit.). Antibodies to the 72-kd antigen were not produced following immunization with killed amastigotes, but antibodies to the 90-kd antigen were. This confirms previous reports that this stage lacks the 72-kd but expresses the 90-kd antigen (Snary ause all anes contai ed antige s of epimastiotes that could be contamin ted wi h antigens the medium used to grow these organisms a rther control was performed in which lanes ith epimastigote m dium were react d with each the antisera employed. No bands were noted et al., 1981, loc. cit.). However, the 90-kd antigen in the amastigote was not affected by treatment with formalin. This suggests that in the amastigote, this antigen is either resistant to or protected against the inactivating capacity of formalin, whereas in the epimastigote, it may be located in a region of the cell membrane, or it is in a form that makes it more susceptible to inactivation by formalin. Infection with blood-form trypomastigotes resulted in formation of antibodies that recognized both the 90and 72-kd antigens of epimastigotes (Lanes 4). This indicates that, contrary to previous reports (Snary et al., 1981, loc. cit.; Nogueira et al., 1981, loc. cit.), either the blood-form trypomastigotes also express the 72-kd antigen, or a stage expressing this epimastigote antigen is present in the vertebrate host. The fact that only immunization with amastigotes resulted in antibodies that clearly and strongly recognized a number of antigens of epimastigotes located between the 21.5and 14.4kd markers is interesting. It may be that these antigens are in a highly immunogenic form in the amastigote; whereas in the epimastigote, they are poorly immunogenic. Supported by the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases and NIH Grant Al 18794. i