Risk analysis and prediction of visceral leishmaniasis dispersion in São Paulo State, Brazil

Abstract

Visceral leishmaniasis (VL) is an important neglected disease caused by a protozoan parasite, and represents a serious public health problem in many parts of the world. It is zoonotic in Europe and Latin America, where infected dogs constitute the main domestic reservoir for the parasite and play a key role in VL transmission to humans. In Brazil this disease is caused by the protozoan Leishmania infantum chagasi, and is transmitted by the sand fly Lutzomyia longipalpis. Despite programs aimed at eliminating infection sources, the disease continues to spread throughout the Country. VL in São Paulo State, Brazil, first appeared in the northwestern region, spreading in a southeasterly direction over time. We integrate data on the VL vector, infected dogs and infected human dispersion from 1999 to 2013 through an innovative spatial temporal Bayesian model in conjunction with geographic information system. This model is used to infer the drivers of the invasion process and predict the future progression of VL through the State. We found that vector dispersion was influenced by vector presence in nearby municipalities at the previous time step, proximity to the Bolívia-Brazil gas pipeline, and high temperatures (i.e., annual average between 20 and 23°C). Key factors affecting infected dog dispersion included proximity to the Marechal Rondon Highway, high temperatures, and presence of the competent vector within the same municipality. Finally, vector presence, presence of infected dogs, and rainfall (approx. 270 to 540mm/year) drove the dispersion of human VL cases. Surprisingly, economic factors exhibited no noticeable influence on disease dispersion. Based on these drivers and stochastic simulations, we identified which municipalities are most likely to be invaded by vectors and infected hosts in the future. Prioritizing prevention and control strategies within the identified municipalities may help halt the spread of VL while reducing monitoring costs. Our results contribute important knowledge to public and animal health policy planning, and suggest that prevention and control strategies should focus on vector control and on blocking contact between vectors and hosts in the priority areas identified to be at risk.

Dispersion of Lutzomyia longipalpis and expansion of visceral leishmaniasis in São Paulo State, Brazil: identification of associated factors through survival analysis

“…Authors have associated the dispersion of the vector and the geographical expansion of VL with the destruction or modification of natural environments, irregular occupation of areas, lack of basic sanitation, poverty, big constructions and migratory flow, among other factors [ 6 , 9 – 15 ]. For example, studies in the states of Mato Grosso do Sul [ 11 ] and São Paulo (SP) [ 16 ] indicated the role of the BR-262 and Marechal Rondon highways (the first one crosses the state of Mato Grosso do Sul from the Bolivian border to the SP border and the second one is its continuation in SP) and the construction of the Bolivia-Brazil gas pipeline in the expansion of human VL in Brazil.…”

“…longipalpis and, consequently, on the occurrence of disease in dogs and humans. Several studies have reported an association between temperature, humidity, and precipitation and vector distribution [ 14 , 15 , 26 – 28 ], as well as with the distribution of canine and human VL [ 15 ].…”

Canine serological survey and dog culling ant its relationship with Human ­Visceral leishmaniasis in an endemic urban area.

“…In addition to the technical issues, the most controversial aspect of canine reservoir elimination has been the ethical question considering the emotional involvement of both the owners and the subjects involved in the culling procedure [33][34][35][36][37][38][39][40][41][42][43][44][45][46]. However, it is noteworthy that HVL is a disease with high lethality if untreated, and it is in the process of geographical expansion [3,47].…”

­Visceral leishmaniasis and control measures in an endemic urban area: space-temporal bayesian analysis

“…However, it is noteworthy that HVL is a disease with high lethality if untreated, and it is in the process of geographical expansion [3,41]. Thus, in order to stop canine reservoir control measures, it is first necessary that there is an efffective alternativepublic health programs.…”