Simian virus 40 sequences in blood specimens from healthy individuals of Casale Monferrato, an industrial town with a history of asbestos pollution. 
Asbestos is considered the main agent in causing the onset of the malignant pleural mesothelioma (MM), a fatal cancer of increasing incidence worldwide.  Other factors may contribute to the onset/progression of MM, such as genetic predisposition and infection by oncogenic viruses, like simian virus 40 (SV40).  SV40 was administered to human populations mainly with SV40-contaminated anti-polio vaccines.  SV40 footprints have been detected in specific human tumours, including MM, and in healthy blood donors.  The aim of this study was to verify the presence of SV40 sequences in buffy coats of healthy blood donors, inhabitants of Casale Monferrato, where MM is 10 times more prevalent compared to other areas.  DNA from 148 buffy coats of healthy blood donors were qualitatively and quantitatively PCR analyzed for SV40 sequences.  SV40 sequences were detected in 24 out of 148 (16%) samples.  Quantitative real time PCR analyses carried out in SV40-positive samples indicated a viral copy number in the range of 10-10,000 per 100,000 cells.  SV40 sequences are present in blood samples of healthy donors from Casale Monferrato with a prevalence similar to that reported in previous investigations of healthy donors from asbestos-free areas.  Altogether these data suggest that SV40 is circulating in the human population.