Environmental and Social Factors Associated with the Occurrence of Severe Tungiasis and Scabies in the State of Ceará, Brazil: An Ecological Study.

Scabies and tungiasis are skin-related neglected tropical diseases (NTDs) associated with poverty and poor living conditions. We performed an ecological study covering a state in northeast Brazil to identify socio-economic and environmental factors associated with the occurrence of severe scabies and severe tungiasis, respectively. Data on disease occurrence on the municipality level were derived from a previous study based on online questionnaires. A total of 47 (26.0%) of the 181 state's municipalities reported severe tungiasis, and 113 (62.4%) severe scabies. Municipalities with occurrence of severe tungiasis were characterized by higher annual rainfalls (median = 883 mm vs. 741 mm; = 0.037), higher minimum temperatures (median = 23.4 °C vs. 22.7 °C; = 0.002), higher aridity indices indicating more humid climates (median = 45.1 vs. 50.6; = 0.019), lower altitudes (median = 88.8 m vs. 201 m; < 0.001), higher mean air humidity (66.5% vs. 63%; = 0.018), and better socioeconomic indices (Municipal Human Development Index [MHDI]-median = 0.616 vs. 0.611; = 0.048/MHDI Longevity-mean = 0.769 vs. 0.759; = 0.007/Municipal Development Index [MDI]-median = 27.5 vs. 21.8; < 0.001). Municipalities with predominant luvisol soil characteristics had a lower risk for severe tungiasis (RR = 0.46; 95% CI = 0.27-0.79; = 0.003), whereas municipalities with predominant gleysols had a significantly higher risk (RR = 2.44; 95% CI = 1.43-4.15; = 0.010). Municipalities with occurrence of severe scabies were characterized by significantly higher annual rainfalls (median = 804 mm vs. 708 mm; = 0.001), higher minimum temperatures (23.1 °C vs. 22.3 °C; < 0.001), higher aridity index (median = 48.2 vs. 41.9; = 0.014), higher air humidity (65.9% vs. 61%; = 0.001), lower altitudes (median = 153 m vs. 246 m; = 0.003), and better socio-economic indicators (MHDI-median = 0.616 vs. 608; = 0.012/MHDI Education-mean = 0.559 vs. 0.541; = 0.014/MDI-median = 24.3 vs. 21.1; = 0.005). In multivariate regression analysis, MDI remained significantly associated with the presence of severe tungiasis in the final model (RR = 1.04; 95% CI: 1.02-1.05; < 0.001) and the presence of severe scabies with minimum temperature (RR = 1.13; 95% CI: 1.04-1.24; = 0.003) and aridity index (RR = 1.01; 95% CI: 1.00-1.01; = 0.004). Our study underscores the importance of environmental and socioeconomic factors for the occurrence of severe scabies and tungiasis in a semi-arid climatic context, offering a perspective for identification of high-risk areas, and providing evidence for the control of skin NTDs withina One Health approach.