Understanding the relationship between the presence of vegetation and the spread of canine visceral leishmaniasis in Camaçari, Bahia State, Northeastern Brazil

Leishmaniasis is a vector-borne disease spread by female phlebotomine sandflies ( Lutzomyia longipalpis ). The most severe form of the disease is visceral leishmaniasis (VL), which can cause fever, hepatosplenomegaly, weight loss and pancytopenia. Domestic canines are the main reservoir for human cases in Brazil because they live in close proximity and can remain asymptomatic for long periods of time. Consequently, sole treatment of human cases will not contain the spread of the disease. Current methods of control have been unsuccessful, and thus a better understanding of the canine transmission and the effect of their environment is required. Vegetation is one of the main risk factors for VL that affects the distribution of phlebotomine sandflies. Using geostatistical models, we aim to further understand the effect of vegetation on canine VL in the community of Camaçari, northeastern Brazil. The risk due to vegetation is quantified using the average of the normalised vegetation index (NDVI) for all pixels within each dog’s home range. We found that an increase in NDVI of 0.1 led to an 1.21-fold increase in the odds of canine visceral leishmaniasis, on average, suggesting that coastal vegetation has a particularly strong correlation with VL. Author summary Leishmaniasis is a disease spread by female phlebotomine sandflies when feeding from mammal blood. Visceral leishmaniasis (VL), the most severe form of the disease, causes fever, weight loss and swelling of internal organs. The vast majority of human VL cases in the Americas occur in Brazil, where domestic canines act as disease pools due to their close proximity to humans and high proportion of asymptomatic cases. Due to a lack of testing and reporting of canine VL cases, authorities have been unable to control transmission. Understanding how VL spreads to canines is imperative to develop new prevention and control strategies. Phlebotomine sandflies feed on plant sap and nectar, and lay eggs around tree roots, hence, we suspect that a mammal would be more likely to contract VL when living near vegetation. We investigated how a dog’s proximity to vegetation affects its chances of contracting VL. We used a geostatistical model that combined the measure of the vegetation with the spatial correlation of the sampled locations of the dogs. Our model estimated that, on average, an increase of 0.1 in the measure of vegetation led to an 1.21-fold increase in the odds that a canine contracted VL. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement Yes ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: All experiments involving animals were performed in accordance with the institutional review board of the Gonçalo Moniz Institute (IGM - Fiocruz - Bahia/Brazil), and were approved by the CEUA of Fiocruz - Bahia (protocol CEUA 017/2010 and 007/2013). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All relevant data are within the paper and its Supporting Information files.