Intestinal schistosomiasis of Ijinga Island, north-western Tanzania: prevalence, intensity of infection, hepatosplenic morbidities and their associated factors.

Background: Intestinal schistosomiasis is highly endemic in Tanzania and mass drug administration (MDA) using praziquantel is the mainstay of the control program. However, the MDA program covers only school aged children and does not include neither adult individuals nor other public health measures. The Ijinga schistosomiasis project examines the impact of an intensified treatment protocol with praziquantel MDA in combination with additional public health interventions. It aims to investigate the feasibility of eliminating intestinal schistosomiasis in a highly endemic African setting using an integrated community-based approach. In preparation of this project, we report about baseline data on S.mansoni prevalence, intensity of infection, related hepatosplenic morbidities and their associated factors.

Methods: A cross sectional study was conducted among 930 individuals aged 1-95 years living at Ijinga Island, north-western Tanzania in September 2016. Single stool and urine samples were collected from each study participant and processed using Kato Katz (KK) technique and point-of-care Circulating Cathodic (POC-CCA) antigen test for detection of S.mansoni eggs and antigen respectively. Ultrasonographical examination for S.mansoni hepatosplenic morbidities was done to all participants. For statistical analyses Fisher's exact test, chi-square test, student-t-test, ANOVA and linear regression were used where applicable.

Results: Overall based on KK technique and POC-CCA test, 68.9% (95%CI: 65.8-71.8) and 94.5% (95%CI: 92.8-95.8) were infected with S.mansoni. The overall geometrical mean eggs per gram (GMepg) of faeces was 85.7epg (95%CI: 77.5-94.8). A total of 27.1, 31.2 and 51.9% of the study participants had periportal fibrosis (PPF-grade C-F), splenomegaly and hepatomegaly. Risk factors for PPF were being male (aRR = 1.08, 95%CI: 1.02-1.16, P < 0.01), belong to the age group 16-25 years (aRR = 1.23, 95%CI: 105-1.44, P < 0.01), 26-35 years (aRR = 1.42, 95%CI: 1.21-1.67, P < 0.001), 36-45 years (aRR = 1.56, 95%CI:1.31-1.84, P < 0.001) and ≥ 46 years (aRR = 1.64, 95%CI:1.41-1.92, P < 0.001). The length of the left liver lobe was associated with being female (P < 0.03), belong to the age group 1-5 years (P < 0.013), 6-15 years (P < 0.04) and S.mansoni intensity of infection (P < 0.034). Male sex (aRR = 1.15, 95%CI:1.06-1.24, P < 0.001) and belonging to the age groups 16-25 years (aRR = 1.27, 95%CI:1.05-1.54, P < 0.02) or 26-35 years (aRR = 1.32, 95%CI:108-1.61, P < 0.01) were associated with splenomegaly.

Conclusion: Schistosoma mansoni infection and its related morbidities (hepatomegaly, splenomegaly, periportal fibrosis) are common in the study area. Age, sex and intensity of infection were associated with periportal fibrosis. The prevalence of S.mansoni was above 50% in each age group and based on the observed prevalence, we recommend MDA to the entire community.