Reemergence of yellow fever: detection of transmission in the State of Sao Paulo, Brazil, 2008

Introduction: Following yellow fever virus (YFV) isolation in monkeys from the Sao Jose do Rio Preto region and two fatal human autochthonous cases from the Ribeirao Preto region, State of Sao Paulo, Brazil, two expeditions for entomological research and eco-epidemiological evaluation were conducted. Methods: A total of 577 samples from humans, 108 from monkeys and 3,049 mosquitoes were analyzed by one or more methods: virus isolation, ELISA-IgM, RT-PCR, histopathology and immunohistochemical. Results: Of the 577 human samples, 531 were tested by ELISA-IgM, with 3 positives, and 235 were inoculated into mice and 199 in cell culture, resulting in one virus isolation. One sample was positive by histopathology and immunohistochemical. Using RT-PCR, 25 samples were processed with 4 positive reactions. A total of 108 specimens of monkeys were examined, 108 were inoculated into mice and 45 in cell culture. Four virus strains were isolated from Alouatta caraya. A total of 931 mosquitoes were captured in Sao Jose do Rio Preto and 2,118 in Ribeirao Preto and separated into batches. A single isolation of YFV was derived from a batch of 9 mosquitoes Psorophora ferox, collected in Urupes, Ribeirao Preto region. A serological survey was conducted with 128 samples from the municipalities of Sao Carlos, Rincao and Ribeirao Preto and 10 samples from contacts of patients from Ribeirao Preto. All samples were negative by ELISA-IgM for YFV. Conclusions: The results confirm the circulation of yellow fever, even though sporadic, in the Sao Paulo State and reinforce the importance of vaccination against yellow fever in areas considered at risk.