Immunity to schistosomiasis before puberty: humeral or cell mediated.

To determine if the cell mediated immunity, induced by T-helper type-1 lymphocytes (Th1) response, during schistosomiasis mansoni has the potential to protect against infection, intensities of infections and re-infections, reflected in the egg count were followed up to 20 months among 119 individuals aged 5-22 years (Ys) with different number of previous infections whose yearly levels and pattern of water contact were similar. They were classified into 5 groups. Delayed hypersensitivity skin tests (DHT) to adult schistosome excretory-secretary antigens (ESAgs) and anti-schistosomula (ESAgs) isotypes were measured on detecting re-infection. The group with a mean age of (8.6 +/- 2.6 Ys) and infected less than 5 times showed only 6.5 percentage reduction of the egg count (PREC) and low cellular and humoral responses. Th1-associated cellular (DHT) and antibody responses (IgG2, IgG3) to the five infections were significantly higher in the (13.5 +/- 1.4 Ys) than in (18 +/- 2.2 Ys) age group. This was reflected in significant difference in PREC; being 41.5% among the first and 13.5% among the second. Th2-associated antibody responses (IgG1, IgG4, IgE) went on rising as patients allowed for age and number of infections increased over 5, being significantly higher in the (19 +/- 1.8 Ys) than in (14 +/- 1.1 Ys) age groups with PREC 45.5% and 12.9% respectively. These results imply a substantial protective role for cell mediated immunity in the pre-puberty stage and provide evidence that Th1-based vaccination strategy can work if augmented.

Diagnosis of early pre-patent schistosomiasis by cystatin capture enzyme-linked immunosorbent assay.

To test the efficacy of detecting anti-Schistosoma mansoni cysteine proteinase antibodies (CP Abs) by cystatin capture (CC) ELISA in the diagnosis of prepatent schistosomiasis (before egg passing); 253 schistosome negative individuals were selected and divided into two groups. The first comprised 118 children whose first water contact occurred in March and April 1999 (primarily infected), and the second 135 individuals were previously treated for schistosomasis (re-infected). All the individuals were followed up triweekly by stool for detecting schistosome eggs and by serological tests for detecting antibodies against CP and anti-soluble egg antigens (SEA) by ELISA technique. CP seropositivity was detected in 92 from all examined individuals, out of them 38 were primarily infected (PI) children (20 of them were pre-patently treated), the rest; 54 were re-infected patients (28 out of them were pre-patently treated). The untreated (44) individuals from both groups were followed up till they passed eggs within 4 weeks and then were treated (post-patent). CP Abs were reassessed for the 92 patients after treatment, only 11 (12%) were still seropositive with marked decrease in optical density (O.D.) level than before treatment. Anti-SEA IgM Abs were sought in the 92 CP seropositive sera, and the seropositivity rate was lower in 38 PI children (5.3%) than in the 54 re-infected individuals (92.6%). The anti-SEA seropositivity rate in the PI children was 5% in the pre-patent and was 94.4% in the post-patent. None of the 161 CP seronegative individuals passed eggs up to 12 weeks.