RESUMO
Schistosomiasis is an aquatic snail borne parasitic disease, with intestinal schistosomiasis (IS) and urogenital schistosomiasis (UGS) caused by Schistosoma mansoni and S. haematobium infections, respectively. School-aged-children (SAC) are a known vulnerable group and can also suffer from co-infections. Along the shoreline of Lake Malawi a newly emerging outbreak of IS is occurring with increasing UGS co-infection rates. Age-prevalence (co)infection profiles are not fully understood. To shed light on these (co)infection trends by Schistosoma species and by age of child, we conducted a secondary data analysis of primary epidemiological data collected from SAC in Mangochi District, Lake Malawi, as published previously. Available diagnostic data by child, were converted into binary response infection profiles for 520 children, aged 6-15, across 12 sampled schools. Generalised additive models were then fitted to mono- and dual-infections. These were used to identify consistent population trends, finding the prevalence of IS significantly increased [p = 8.45e-4] up to 11 years of age then decreasing thereafter. A similar age-prevalence association was observed for co-infection [p = 7.81e-3]. By contrast, no clear age-infection pattern for UGS was found [p = 0.114]. Peak prevalence of Schistosoma infection typically occurs around adolescence; however, in this newly established IS outbreak with rising prevalence of UGS co-infections, the peak appears to occur earlier, around the age of 11 years. As the outbreak of IS fulminates, further temporal analysis of the age-relationship with Schistosoma infection is justified. This should refer to age-prevalence models which could better reveal newly emerging transmission trends and Schistosoma species dynamics. Dynamical modelling of infections, alongside malacological niche mapping, should be considered to guide future primary data collection and intervention programmes.
RESUMO
BACKGROUND: Intestinal schistosomiasis was not considered endemic in Lake Malawi until November 2017 when populations of Biomphalaria pfeifferi were first reported; in May 2018, emergence of intestinal schistosomiasis was confirmed. This emergence was in spite of ongoing control of urogenital schistosomiasis by preventive chemotherapy. Our current study sought to ascertain whether intestinal schistosomiasis is transitioning from emergence to outbreak, to judge if stepped-up control interventions are needed. METHODS: During late-May 2019, three cross-sectional surveys of primary school children for schistosomiasis were conducted using a combination of rapid diagnostic tests, parasitological examinations and applied morbidity-markers; 1) schistosomiasis dynamics were assessed at Samama (n = 80) and Mchoka (n = 80) schools, where Schistosoma mansoni was first reported, 2) occurrence of S. mansoni was investigated at two non-sampled schools, Mangochi Orphan Education and Training (MOET) (n = 60) and Koche (n = 60) schools, where B. pfeifferi was nearby, and 3) rapid mapping of schistosomiasis, and B. pfeifferi, conducted across a further 8 shoreline schools (n = 240). After data collection, univariate analyses and Chi-square testing were performed, followed by binary logistic regression using generalized linear models, to investigate epidemiological associations. RESULTS: In total, 520 children from 12 lakeshore primary schools were examined, mean prevalence of S. mansoni by 'positive' urine circulating cathodic antigen (CCA)-dipsticks was 31.5% (95% confidence interval [CI]: 27.5-35.5). Upon comparisons of infection prevalence in May 2018, significant increases at Samama (relative risk [RR] = 1.7, 95% CI: 1.4-2.2) and Mchoka (RR = 2.7, 95% CI: 1.7-4.3) schools were observed. Intestinal schistosomiasis was confirmed at MOET (18.3%) and Koche (35.0%) schools, and in all rapid mapping schools, ranging from 10.0 to 56.7%. Several populations of B. pfeifferi were confirmed, with two new eastern shoreline locations noted. Mean prevalence of urogenital schistosomiasis was 24.0% (95% CI: 20.3-27.7). CONCLUSIONS: We notify that intestinal schistosomiasis, once considered non-endemic in Lake Malawi, is now transitioning from emergence to outbreak. Once control interventions can resume after coronavirus disease 2019 (COVID-19) suspensions, we recommend stepped-up preventive chemotherapy, with increased community-access to treatments, alongside renewed efforts in appropriate environmental control.