Impact of 4% Deltamethrin-Impregnated Dog Collars on the Incidence of Human Visceral Leishmaniasis: A Community Intervention Trial in Brazil

Abstract

Background: In Brazil, human visceral leishmaniasis (HVL) is caused by the protozoan parasite Leishmania infantum, primarily transmitted by the sand fly Lutzomyia longipalpis, with dogs acting as the main urban reservoir. This study aims to evaluate the effectiveness of 4% deltamethrin-impregnated dog collars (DMC) on HVL incidence. Methods: This is a community intervention study carried out from 2012 to 2015 in the municipalities of Araguaína, State of Tocantins, and Montes Claros, State of Minas Gerais, Brazil. Two areas in each were randomly allocated to either (1) culling seropositive dogs + residual insecticide spraying (control area—CA) or (2) culling seropositive dogs + residual insecticide spraying + DMC fitted to dogs every six months for two years (intervention area—IA). Cases of HVL (n = 1202) occurring from 2008 to 2020 were identified from the Brazilian Reportable Diseases Information System and georeferenced to the control and intervention areas. The HVL cases from 2008 to 2012 were considered as occurring in the “pre-intervention” period. Those cases from 2013 to 2016 and from 2017 to 2020 were regarded as occurring in the “intervention” and “post-intervention” periods, respectively. We used a mixed-effects Poisson regression model to estimate the effectiveness of the intervention, comparing the changes from the pre-intervention period to the intervention and post-intervention periods in the control and intervention areas. Results: In Araguaína, there was a statistically significant reduction in the incidence of HVL in both the control and intervention areas, comparing both the intervention and post-intervention periods with the pre-intervention period. The intervention with DMC was significantly associated with a reduction in HVL when comparing the intervention and pre-intervention periods, yielding an effectiveness estimate of the DMC of 27% (IC95% 1–46%, p = 0.045). No differences were observed when comparing the pre- and post-intervention periods (p = 0.827). In Montes Claros, cases reduced in both the control and intervention areas from the pre-intervention period to the intervention period (p = 0.913). In the post-intervention period, the incidence increased in the control area, while cases continued to decrease in the DMC area (p = 0.188). Conclusions: The use of DMC was associated with a reduction of 27% in the incidence of HVL during the period of DMC delivery, indicating that DMC is effective as an additional strategy for controlling visceral leishmaniasis in Brazil. However, no significant reduction associated with DMC was detected after the intervention period, suggesting that a control program based on the large-scale deployment of DMC might have to be maintained for more extended periods without interruption.

Canine leishmaniasis in the Americas: etiology, distribution, and clinical and zoonotic importance

“…Leishmania infantum clearly expanded southwards in recent decades and is now endemic to parts of the southern cone of South America, including Uruguay. Considering the clinical importance of canine leishmaniasis and the limited treatment availability in the Americas, the use of preventive measures [ 55 , 72 – 74 , 87 – 89 ] is key to mitigating the risk of infection in uninfected dogs. This may also minimize the role of infected dogs as reservoirs, which is pivotal to reduce the risk of infection in humans and other susceptible animals, including cats.…”

“…Since 2009, an extraordinary number of field and laboratory studies on canine leishmaniasis in the Americas have been published in international literature. These include epidemiological studies focused on prevalence and risk factors (e.g., [ 67 , 68 ]), studies validating new diagnostic tools (e.g., [ 69 ]), and clinical trials assessing the efficacy or effectiveness of therapeutic protocols (e.g., [ 70 ]) and prevention and control strategies (e.g., [ 71 , 72 ]). The unified efforts of scientists, nongovernmental organizations [e.g., the Brasileish group ( https://www.brasileish.com.br )], and public health authorities effectively contributed to positively changing our practices in terms of the diagnosis, treatment, prevention, and control of canine leishmaniasis, particularly in Brazil, where mass culling of seropositive dogs is no longer a common practice, 4% deltamethrin-impregnated dog collars are often applied to dogs in high-risk areas, and miltefosine is now licensed for use in dogs [ 55 , 73 , 74 ].…”