The Reverse Path: New Cycle of Canine Visceral Leishmaniasis Transmission From the Urban Area to the Peri-Urban Area and Rural Area in a Vulnerable Region of the State of São Paulo

Visceral leishmaniasis (VL) is a zoonosis of public health relevance and is considered neglected. The municipality of Teodoro Sampaio (TS), known as the “capital of Pontal do Paranapanema,” in the west of São Paulo state, is located in one of the most vulnerable regions of the state. Recently, it was classified as high priority by the Ministry of Health (MS), indicating high risk of VL infection and need for intervention. In São Paulo, VL expansion occurs predominantly in urban areas, and its spread to rural areas is an event still in progress. This study evaluated the evolution of canine visceral leishmaniasis (CVL) in TS, focusing on the possible transition of the transmission cycle from the urban area to peri-urban and rural regions. Retrospective study using data from the Unidade de Vigilância em Zoonoses of the Secretaria Municipal de Saúde of TS and the Instituto Adolfo Lutz (Presidente Prudente), between 2012 and 2023. Surveillance was based on suspected cases or serological surveys. Confirmation followed MS guidelines, using concordance between the dual-platform rapid immunochromatographic test and the enzyme immunoassay. Systematic CVL surveillance in rural areas began in 2022. The estimated canine population was 5,754 animals (1 dog/4 inhabitants, 2020 reference). Data were expressed as mean ± standard error of the mean with 95% confidence intervals (95% CI). Between 2012–2023, 7,718 dogs were investigated (643 ± 105.4; 95% CI: 411.2–875.1; range: 174–1417). A total of 2,376 positive CVL cases were diagnosed (182.8 ± 93.7; 95% CI: 21.4–386.9; range: 1–1188), representing 130.7% of the estimated population. The years with the highest incidence were 2021 to 2023, with 1078/2376 (45.2%) of cases. In 2022/2023, the beginning of rural surveillance, 40/703 (5.7%) of positive dogs belonged to peri-urban or rural residents, with 11/40 (27.5%) residing in rural settlements. The high detection of CVL cases, including in peri-urban and rural areas, indicates the possible establishment of a new transmission cycle, with the disease shifting from the urban environment to rural zones, reversing the trend observed in the introduction of VL in the state.