In examining the hypothesis that PD could stem from an influenza virus infection that develops into encephalitis lethargica the role of bacterial and viral infections as a possible cause of Parkinsonism is questioned. The paper compares the clinical, histological, and structural features of Parkinsonism in infectious diseases and looks at the influenza virus and why and how it became associated with PD. Herpes Simplex Virus 1; Epstein-Barr Virus; Varicella-Zoster Virus; Hepatitis C; the Japanese Encephalitis Virus and the West Nile Virus are discussed in connection with PD. The review also examines the Human Immunodeficiency Virus (HIV) and Parkinsonism. In conclusion, the synergistic effect of infectious pathogens in inducing neuroinflammation leading to PD development has been observed. However, it cannot be established that all cases of PD are associated with increased inflammation and underlying chronic infection. Further research is necessary to examine the involvement and extent to which pathogens and inflammatory cytokines play in the pathomechanism of PD.

Source: Infectious Etiologies of Parkinsonism: Pathomechanisms and Clinical Implications