Understanding the relationship between the presence of vegetation and the spread of canine visceral leishmaniasis in Camacari, 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 Camacari, northeastern Brazil. The risk due to vegetation is quantified using the average of the normalised vegetation index (NDVI) for all pixels within each dogs 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 summaryLeishmaniasis 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 dogs 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.