Effectiveness of Insecticide Spraying and Culling of Dogs on the Incidence of Leishmania infantum Infection in Humans: A Cluster Randomized Trial in Teresina, Brazil

Abstract

BackgroundTo evaluate the effect of insecticide spraying for vector control and elimination of infected dogs on the incidence of human infection with L. infantum, a randomized community intervention trial was carried out in the city of Teresina, Brazil.Methods/Principal FindingsWithin each of ten localities in the city, four blocks were selected and randomized to 4 interventions: 1) spraying houses and animal pens with insecticide; 2) eliminating infected dogs; 3) combination of spraying and eliminating dogs, and 4) nothing. The main outcome is the incidence of infection assessed by the conversion of the Montenegro skin test (MST) after 18 months of follow-up in residents aged ≥1 year with no previous history of visceral leishmaniasis (VL). Reactions were measured at 48–72 h, induration of ≥5 mm considered positive. Interventions were executed after the baseline interview and repeated 6 and 12 months later. The effects of each type of intervention scheme on the incidence of infection were assessed by calculating relative risks and 95% confidence intervals using Poisson population-averaged regression models with robust variance. Among the 1105 participants, 408 (37%) were MST positive at baseline. Of the 697 negatives, only 423 (61%) were reexamined at the end of the follow-up; 151 (36%) of them converted to a positive MST. Only dog culling had some statistically significant effect on reducing the incidence of infection, with estimates of effectiveness varying between 27% and 52%, depending on the type of analysis performed.Conclusions/SignificanceIn light of the continuous spread of VL in Brazil despite the large scale deployment of insecticide spraying and dog culling, the relatively low to moderate effectiveness of dog culling and the non-significant effect of insecticide spraying on the incidence of human infection, we conclude that there is an urgent need for revision of the Brazilian VL control program.

Uso e cobertura do solo e prevalência de leishmaniose visceral canina em Teresina, Piauí, Brasil: uma abordagem utilizando sensoriamento remoto orbital

“…Dogs (Canis familiaris) have been incriminated as the parasite's principal domestic reservoir in urban areas, providing the basis for culling infected dogs as one of the control strategies for VL in Brazil 5 , although the strategy has not produced the desired effect of interrupting spread of the disease, besides the relative lack of studies demonstrating its effectiveness 6,7 . Even given the known importance of dogs as a key source of the infection in urban areas, there are still huge gaps in the knowledge on factors associated with L. infantum infection in these animals 8 .…”

Effectiveness of the Brazilian Visceral Leishmaniasis Surveillance and Control Programme in reducing the prevalence and incidence of Leishmania infantum infection

“…In the study by Souza et al [22], although the data suggested a small reduction in the incidence of human infection in areas of intervention when compared with the control area, the difference was not statistically significant. The study by Werneck et al [10] compared different control strategies and showed the low effectiveness of the euthanasia of dogs on the incidence of human infection. On the other hand, a study by Costa et al [33] pointed towards a protective effect of the euthanasia of infected dogs in the human incidence of L. infantum infection associated with intra-domicile spraying.…”

“…In a systematic review analyzing intervention studies on the effectiveness of VL control programmes that included strategies to reduce the risk of transmission, such as animal reservoir control, vector control with insecticide spraying, or a combination of these interventions, Romero & Boelart [4] concluded that there is a lack of scientific evidence to sustain the effectiveness of these interventions in interrupting the spread of the disease. A randomized community intervention trial evaluating the impact of insecticide spraying and elimination of infected dogs on the incidence of human L. infantum infection showed that only dog culling reduced the human incidence, with estimates of effectiveness varying between 27–52%, depending on the analysis performed [10]. …”

Risk Profiles for Leishmania infantum Infection in Brazil

“…This is a cohort study based on a cluster randomized trial 13 Ten localities in seven neighborhoods in different regions of the city encompassing varied contexts regarding urbanization, vegetation cover, and patterns of disease transmission were selected for the study. All the selected localities had a history of recent occurrence of new cases of VL.…”

“…Finally, it was also asked whether the participants used insecticide inside the house. Considering that the estimates of the effectiveness of all interventions were quite similar and nonsignificant after correction for bias due to selective loss to follow up, 13 we decided to split to create a dichotomous variable indicating whether the area where the household was located had been allocated to receive some type of intervention in the background study: intervention area (area that received some type of intervention, i.e., areas A, B, and C) and nonintervention area (area that did not receive any intervention, i.e., area D). Study outcome was the cumulative incidence (CI) of L. infantum infection at 18 months as measured by Montenegro's test conversion.…”