Epidemiology of Schistosoma mansoni infection in sympatric humans and non-human primates in the Gombe ecosystem Tanzania

Increased interactions between humans and wild animals in and around protected areas have raised the risks for sharing diseases and parasites among them. Regular surveillance with intervention for these infections in such areas is therefore necessary for improving animal health and for controlling any spill-over of animal diseases into nearby human populations. Although both humans and non-human primates in the Gombe area in western Tanzania are infected with schistosomiasis, it is not known whether strains of their schistosomes are epidemiologically and genetically distinct. The distribution and transmission risk factors for the disease in these areas are also not well known. This study investigated the infection patterns of schistosomiasis in humans and non-human primates in Gombe National Park and surrounding villages of Mwamgongo, Bugamba, Kiziba and Mtanga and related the infection prevalence and intensity to locality and other demographic characteristics such as age and sex in humans. It also examined the dosage and number of praziquantel tablets administered to school children based on their weight and compared this to the dosage they would receive based on their height. The parasite fauna of baboons and vervet monkeys in Gombe was also examined to determine the parasite species assess whether their infection levels have changed over time. Snails were also sampled so as to gain a clear understanding of the species present in an area, their local distribution and infection status. The results showed a significant variation of S. mansoni prevalence between age groups in humans, which also depended on site. The parasite egg counts (intensity) also varied significantly between age groups and across study sites. The dosage range of praziquantel in mg per kg of bodyweight predicted by height was 23-43 (average: 35.2) while the dosage range given to children based on their weight was 29-78 (average: 45.2) and this variation was statistically significant (p > 0.0001). Overall, six children (5.3%) received a praziquantel dosage below the recommended range (30-60 mg/kg) based on their weight while two children (2.6%) would have received the drugs above the optimum range based on their height. The parasites identified in baboons and vervets included Trichuris spp., Physaloptera spp., hookworms and unidentified nematodes, while Paragonimus spp., Streptopharagus spp. and Schistosoma mansoni were exclusively detected in baboons. Molecular analysis of baboon schistosome eggs confirmed them to be S. mansoni. A GLM analysis indicated that the interaction between season and baboon troop was a significant predictor of parasite prevalence and intensity in baboons. Snails obtained from all streams except at Mtanga were identified as Biomphalaria pfeifferi based on morphology and DNA analysis. These findings indicate a high infection of intestinal schistosomiasis in these areas of western Tanzania, suggesting that the distribution of the disease in the country could be more widespread than previously thought. The results also confirm that the infection of intestinal schistosomiasis in the area is focal, with marked variations between adjacent villages. The study shows that while both weight and height estimate the amount of praziquantel dosage that is within an acceptable range, weight tends to underestimate the drug while height slightly overestimates it. It is therefore essential to conduct further field studies to test the usefulness of the dose pole in praziquantel distribution and evaluate the extent to which the method could be wasting the drug by giving more than the necessary dosage. As most parasites diagnosed in baboons and vervets are capable of infecting humans, these animals can potentially serve as reservoirs of human helminths given the regular human-wildlife interactions in the area. The implication of these observations to wildlife conservation and public health issues in the area has been explored