Efficacy of 4 % deltamethrin-impregnated collars against canine visceral leishmaniasis across different areas and the sociocultural burden of collar loss in a middle-income country.

Despite efforts to control visceral leishmaniasis (VL), the disease remains a major burden in low- and middle-income countries. In South America, insecticide-impregnated dog collars help prevent disease transmission, as dogs are the main reservoirs in urban areas. This study evaluated the efficacy of 4 % deltamethrin-impregnated collars (DMC) against canine VL (CVL) over a 24-month period in an endemic area of Brazil. We compared 941 DMC dogs with 1032 control dogs (C) across four geographic areas with similar baseline disease prevalence. The difference between the DMC and C cohorts was statistically significant (p < 0.05), and the study achieved an overall efficacy of 63 %, 51 %, 48 %, and 58 % at the first, second, third, and fourth follow-ups, respectively. Among dogs that remained protected, efficacy was 74 %, 67 %, 100 %, and 100 % across the follow-ups, whereas in dogs that lost their collars between follow-ups, efficacy was 45 %, 10 %, 23 %, and - 11 %. Collar loss between follow-ups was associated with a 2.25-fold increase in the odds of CVL (OR 2.25, p < 0.05). No statistically significant geographical variation in collar loss was observed, and most losses were potentially preventable. However, infrequently bathed dogs had significantly higher odds of CVL (OR 9.93, p < 0.05). These results help demystify sociocultural stigmas related to collar loss and support the development of targeted public health education initiatives. Ensuring collar retention, incorporating owners' cultural behaviors to promote consistent collar use, and integrating educational actions within the One Health and Health Promotion frameworks are crucial to maximizing the success of large-scale dog interventions in public health.