Canine visceral leishmaniasis : incidence and risk factors for infection in a cohort study in Brazil.

Abstract

Zoonotic visceral leishmaniasis in Brazil is caused by Leishmania infantum parasites andis transmitted by sand flies of the Phlebotominae family. Dogs are the main urban reser-voirs and represent the major source of contagion for the vectors. Studies have shown thatmost infected dogs are polymerase chain reaction-positive months before seroconversion.Herein, we describe a cohort study designed to identify the incidence of and risk factorsfor L. infantum infection as detected by polymerase chain reaction-restriction fragmentlength polymorphism. To determine the risk factors for infection, we conducted a base-line canine survey (n = 1443) from which dogs were selected for the cohort study (n = 282)involving three evaluations over the course of a 26-month follow-up period. Serology,molecular tests, and a structured questionnaire were used. The risk factors for infectionwere identified by means of the Cox regression model. The overall infection incidencewas 5.8 per 100 dog-months (95% confidence interval 5.1–6.5). Increased risk of infec-tion was associated with the presence of previous cases of canine visceral leishmaniasis inthe domiciles (hazard ratio [HR] 1.4; 95% confidence interval [CI] 1.1–1.8) and unplasteredhouse walls (HR 3.6; 95% CI 1.6–8.1). These risk factors suggest that insecticide spraying incracks and crevices in unplastered walls can reduce biting rates within and around homes.Furthermore, our results demonstrate that the Visceral Leishmaniasis Control and Surveil-lance Program should adopt environmental management measures in homes with previouscases of canine visceral leishmaniasis, because these homes are more likely to maintain thetransmission cycle.