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Spatio-temporal modelling of Leishmania infantum infection among domestic dogs: a simulation study and sensitivity analysis applied to rural Brazil.

ABSTRACT: BACKGROUND:The parasite Leishmania infantum causes zoonotic visceral leishmaniasis (VL), a potentially fatal vector-borne disease of canids and humans. Zoonotic VL poses a significant risk to public health, with regions of Latin America being particularly afflicted by the disease. Leishmania infantum parasites are transmitted between hosts during blood-feeding by infected female phlebotomine sand flies. With a principal reservoir host of L. infantum being domestic dogs, limiting prevalence in this reservoir may result in a reduced risk of infection for the human population. To this end, a primary focus of research efforts has been to understand disease transmission dynamics among dogs. One way this can be achieved is through the use of mathematical models. METHODS:We have developed a stochastic, spatial, individual-based mechanistic model of L. infantum transmission in domestic dogs. The model framework was applied to a rural Brazilian village setting with parameter values informed by fieldwork and laboratory data. To ensure household and sand fly populations were realistic, we statistically fitted distributions for these entities to existing survey data. To identify the model parameters of highest importance, we performed a stochastic parameter sensitivity analysis of the prevalence of infection among dogs to the model parameters. RESULTS:We computed parametric distributions for the number of humans and animals per household and a non-parametric temporal profile for sand fly abundance. The stochastic parameter sensitivity analysis determined prevalence of L. infantum infection in dogs to be most strongly affected by the sand fly associated parameters and the proportion of immigrant dogs already infected with L. infantum parasites. CONCLUSIONS:Establishing the model parameters with the highest sensitivity of average L. infantum infection prevalence in dogs to their variation helps motivate future data collection efforts focusing on these elements. Moreover, the proposed mechanistic modelling framework provides a foundation that can be expanded to explore spatial patterns of zoonotic VL in humans and to assess spatially targeted interventions.

SUBMITTER: Buckingham-Jeffery E

PROVIDER: S-EPMC6505121 | biostudies-literature | 2019 May

REPOSITORIES: biostudies-literature

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Spatio-temporal modelling of Leishmania infantum infection among domestic dogs: a simulation study and sensitivity analysis applied to rural Brazil.

Buckingham-Jeffery Elizabeth E Hill Edward M EM Datta Samik S Dilger Erin E Courtenay Orin O

Parasites & vectors 20190507 1

<h4>Background</h4>The parasite Leishmania infantum causes zoonotic visceral leishmaniasis (VL), a potentially fatal vector-borne disease of canids and humans. Zoonotic VL poses a significant risk to public health, with regions of Latin America being particularly afflicted by the disease. Leishmania infantum parasites are transmitted between hosts during blood-feeding by infected female phlebotomine sand flies. With a principal reservoir host of L. infantum being domestic dogs, limiting prevalen ...[more]

PMID: 31064395

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Project description:BackgroundThe sand fly Nyssomyia neivai is one of the most abundant species in Southern Brazil. It is frequently found in areas that are foci of visceral leishmaniasis in the state of Santa Catarina, caused by Leishmania infantum. In this region, the main vector of L. infantum, Lutzomyia longipalpis, has not been detected. In the absence of L. longipalpis, this study aimed to identify the sand fly fauna and diagnose any potential Leishmania spp. infection in sand flies and in dogs in a region of Southern Brazil that experienced a recent canine visceral leishmaniasis outbreak.MethodsThis report includes a survey of the sand fly fauna at the Zoonosis Control Center of the Municipality of Tubarão (Santa Catarina, Brazil). Molecular tests were conducted to investigate Leishmania spp. natural infection in sand flies using polymerase chain reaction (PCR). In positive females, in addition to morphological identification, molecular analysis through DNA barcoding was performed to determine the sand fly species. Additionally, the dogs were tested for the presence of Leishmania spp. using a non-invasive technique for the collection of biological material, to be assessed by PCR.ResultsA total of 3419 sand flies, belonging to five genera, were collected. Nyssomyia neivai was the most abundant species (85.8%), followed by Migonemyia migonei (13.3%), Pintomyia fischeri (0.8%), Evandromyia edwardsi (< 0.1%), and species of the genus Brumptomyia. (0.1%). Out of the 509 non-engorged females analyzed by PCR, two (0.4%) carried L. infantum DNA. The naturally infected females were identified as Ny. neivai, in both morphological and molecular analysis. In addition, two out of 47 conjunctival swabs from dogs tested positive for L. infantum, yielding an infection rate of 4.2%.ConclusionsThese results confirm the presence of Ny. neivai naturally infected with L. infantum in an area where dogs were also infected by the parasite, suggesting its potential role as a vector in Southern Brazil.

Project description: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.

Dataset Information

Spatio-temporal modelling of Leishmania infantum infection among domestic dogs: a simulation study and sensitivity analysis applied to rural Brazil.

Publications

Spatio-temporal modelling of Leishmania infantum infection among domestic dogs: a simulation study and sensitivity analysis applied to rural Brazil.

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