Housing structure including the surrounding environment as a risk factor for visceral leishmaniasis transmission in Nepal

Author summary Visceral leishmaniasis (VL) is a fatal disease if not treated in time. It is the disease of the poorest people. Poor housing and sanitation around the house are considered as the risk factors for the occurrence of VL. The main objective of our research was to explore multiple risk factors from different housing and land lot- typologies for VL occurrence and transmission through a case-control study. Some of our results reveal that inside the dwelling the likelihood of having clinical VL was substantially enhanced by providing suitable breeding sites for the insect vectors; as an example: the probability of getting VL disease was about ten times higher when there were sacks (empty or filled) near sleeping areas. Also cracks in walls and floors were found to contribute to vector transmission but also particular wall structures such as bamboo walls, and finishes such as animal manure were shown to be optimal for vector breeding. Furthermore, certain animals and plant types in the immediate environment seem to attract the vectors and to have a substantial effect on VL occurrence. Thus, given the alarming increase of VL in previously non-endemic areas of Nepal, these findings, among others, will allow readers and policymakers to better understand the hidden VL transmission factors, and will-hopefully- encourage initiating future studies. Visceral leishmaniasis (VL) in Nepal is found in 61 out of 75 districts including areas previously listed as non- endemic. This study focused on the role of housing conditions and its immediate environment in VL transmission, to limit future transmissions, ensure sustainable vector control and support the VL elimination program. The objective was to explore the risk factors in rural housing-and land lot typologies contributing to clinical VL occurrence and transmission. Housing structures and land lots were examined based on characteristics as risk factors of VL transmission in a case-control analysis. VL cases from 2013-2017 were identified based on the existing database from the Epidemiology and Disease Control Division and District Public Health Office from the plain Terai area (Morang, and Saptari districts) and hilly area (Palpa district) of Nepal. Two hundred and three built environments were analyzed (66 cases and 137 controls). Inferential statistics and logistic regression analysis were performed to determine the association of risk factors with VL. The risk factors with the highest odds of VL were: bamboo walls (adjusted odds ratio (AOR)- 8.1, 95% CI 2.40-27.63, p = 0.001), walls made of leaves/branches (AOR- 3.0, 95% CI 0.84-10.93, p = 0.090), cracks in bedroom walls (AOR- 2.9, 95% CI 0.93-9.19, p = 0.065), and placing sacks near sleeping areas (AOR- 19.2, 95% CI 4.06-90.46, p <0.001). Significant outdoor factors were: lots with Kadam trees (AOR- 12.7, 95% CI 3.28-49.09, p <0.001), open ground-outdoor toilets (AOR- 9.3, 95% CI 2.14-369.85, p = 0.003), moisture in outdoor toilet sheds (AOR- 18.09, 95% CI 7.25-451.01, p = 0.002), nearby- open land (AOR- 36.8, 95% CI 3.14-430.98, p = 0.004), moisture inside animal sheds (AOR- 6.9, 95% CI 1.82-26.66, p = 0.005), and surrounding animals/animals wastes particularly goats (AOR- 3.5, 95% CI 1.09-10.94, p = 0.036). Certain housing and surrounding environmental conditions and characteristics are risk factors for VL. Hence, elimination and educational programs should include the focus on housing improvement and avoidance of risk factors. Longitudinal interventional studies are required to document temporal relationships and whether interventions on these factors will have an impact on Leishmania transmission or burden.