Topic: Xenomonitoring of Schistosoma intermediate hosts for evaluating community-wide mass drug administration in Ghana: preliminary findings and lessons.

BACKGROUND

Monitoring the impact of schistosomiasis mass drug administration (MDA) relies mainly on human sampling, which is resource intensive and raises ethical and logistical challenges. Xenomonitoring of intermediate host snails offers a non-invasive alternative; however, its utility for program evaluation in Ghana remains unexplored.

METHODS

We conducted longitudinal snail sampling at 31 human-water contact points along Weija Lake, Ghana, 1 month before and at five time points up to 18 months after two rounds of community-wide praziquantel MDA. Snails were identified morphologically, examined for cercarial shedding and assessed by species-specific cyclooxygenase 1 polymerase chain reaction for Schistosoma mansoni, Schistosoma haematobium and Schistosoma bovis. Prevalence changes were analysed using χ2 tests, pairwise comparisons with Bonferroni correction and logistic regression. Human stools and urine were collected at the same time points for parasitological analysis.

RESULTS

Of 2201 snails collected, 74.7% were Bulinus spp. and 25.3% were Biomphalaria spp. Human-specific Schistosoma infections decreased from 2.8% at baseline to 0.6% 2 months after the first MDA and 0.4% 6 months after the second MDA (p<0.05). Logistic regression analysis indicated significantly lower odds of infection at these time points compared with baseline. However, prevalence rebounded at intervening time points and mixed S. haematobium-S. bovis infections were common. The prevalence pattern in humans mirrored that of snails.

CONCLUSIONS

This first Ghanaian study demonstrates the potential of snail xenomonitoring to detect temporal changes in transmission following community-wide MDA. While findings support its value as a complementary monitoring tool, methodological refinements and parallel human-snail surveys are needed before program adoption.