Objective To investigate the effect of Lead (Pb) acetate exposure on Semliki forest vires (SFV) pathogenesis in mice. Methods Different doses (62.5, 125, 250 and 500 mg/Kg body weight) of Pb dissolved in normal saline were given to mice by oral intubation in a sub-acute (28 days) and sub-chronic (90 days) regimen followed by SFV infection. Morbidity, mortality, clinical symptoms, mean survival time (MST), changes in body and organ weight, accumulation of lead in soft tissues, virus titre in brain and histopathological alterations were compared between lead exposed and infected groups. Results Early appearance of virus symptoms, increased mortality, decreased MST, enhanced SFV titre and greater tissue damage were observed in lead exposed-SFV-infected mice. Conclusion Pre-exposure to lead increases the susceptibility of mice towards SFV infection. Further studies are suggested in view of the persistence of lead in the environment and the possibility of infection by microbial pathogens. Objective To investigate the effect of Lead (Pb) acetate exposure on Semliki forest vires (SFV) pathogenesis in mice. Methods Different doses (62.5, 125, 250 and 500 mg / Kg body weight) of Pb dissolved in normal saline were given to mice by oral intubation in a sub-acute (28 days) and sub-chronic (90 days) regimen followed by SFV infection. Morbidity, mortality, clinical symptoms, mean survival time (MST), changes in body and organ weight, accumulation of lead in early soft tissue, virus titre in brain and histopathological alterations were compared between lead exposed and infected groups. Results Early appearance of virus symptoms, increased mortality, decreased MST, enhanced SFV titre and greater tissue damage were observed in lead exposed-SFV-infected mice . Conclusion Pre-exposure to lead increases the susceptibility of mice towards SFV infection. Further studies are suggested in view of the persistence of lead in the environment and the possibility of infection by microbial pathogens.