Abstract
Visceral leishmaniasis (VL) has recently emerged in various urban and peri-urban areas of Brazil and other countries. Understanding the urbanization of VL requires identification of risk factors associated with human and canine infection. To determine the predictors of risk for canine VL, a survey was conducted of 1,443 dogs, from which a cohort was selected (n = 455) and evaluated for approximately 26 months. Serology was conducted with two enzyme-linked immunosorbent assays (ELISA): one conducted in the Laboratory of Zoonosis of the Belo Horizonte Health Department (LZOON) and the other in the Laboratory of Immunopathology of the Federal University of Ouro Preto (LIMP). A molecular diagnostic method (PCR–restriction fragment length polymorphism) and a structured questionnaire were also used. To identify the factors associated with seroconversion, two time-dependent Cox regression models were performed with different sensitivities (model 1, seroconversion by ELISA/LZOON; model 2, seroconversion by ELISA/LIMP). The overall incidences of seroconversion were 6.5/1000 dogs-months and 11.2/1000 dogs-months for ELISA/LZOON and ELISA/LIMP, respectively. Increased risk of seroconversion was associated with short fur (model 1: hazard ratio [HR] 1.9), the presence of dry leaves (model 1: HR 2.8) or manure (model 1: HR 3.5) in the backyard, dogs sleeping predominantly in the backyard (model 2: HR 2.1), the presence of symptoms (model 2: HR 2.0), and positive molecular results during follow-up (model 2: HR 1.5). Decreased risk was associated with insecticide spraying in the house (model 2: HR 0.5). These results indicate that more-vulnerable domiciles, certain dog behaviors, lack of vector control measures, and positive molecular results were associated with the occurrence of canine VL. Furthermore, it is important to emphasize that PCR-positive dogs should be monitored, owing to the possibility of seroconversion. Identifying risk factors for seroconversion in dogs is crucial for developing adequate strategies for VL prevention and control.
Highlights
Visceral leishmaniasis (VL) is a neglected disease with an estimated incidence of 500,000 new cases and 59,000 deaths annually [1]
The field work was done in close collaboration with the Municipality Health Service, and the data were collected during the canine survey census conducted by health agents as part of Visceral Leishmaniasis Control and Surveillance Program (VLCSP)’s routine
Incidence of seroconversion detected by enzyme-linked immunosorbent assays (ELISA)/LZOON was associated with short fur (HR 1.9; 95% confidence interval (CI) 1.1–3.4) and with the presence of dry leaves (HR 2.8; 95% CI 1.6– 5.0) and manure (HR 3.5; 95% CI 1.3–9.7) in the backyard
Summary
Visceral leishmaniasis (VL) is a neglected disease with an estimated incidence of 500,000 new cases and 59,000 deaths annually [1]. Brazil is the only country where seropositive dogs are systematically removed [5] Despite these measures, the number of reported human cases increased from 1,944 in 1990 to 3,894 in 2011 [6,7]. A cross-sectional study conducted demonstrated that factors associated with early L. infantum infection were the lower socioeconomic status of the owner, dog behavior, the owner’s knowledge about the vector, and the care given to the dogs [12]. We report the results of a concurrent cohort study that was designed to estimate the incidence rate of seroconversion in dogs over time and to identify the risk factors associated with seroconversion, including the domiciliary and peridomiciliary environment, the socioeconomic status of the owners, the care given to the animals, and the animals’ characteristics and behavior. Dynamic survival models of the extended Cox model were used to capture the time variation of the relationships between the variables
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