<qa>  What is the concept of co-pathogenesis?Recent observations from retrospective cohort studies indicate that HIV-associated tuberculosis TB is associated with reduced survival and increased rate of opportunistic infections compared to CD4-matched controls. Mounting evidence from immunologic and virologic studies supports the concept of co-pathogenesis, in which cytokines such as tumor necrosis factor alpha TNF alpha are over-expressed during the course of TB and stimulate viral replication in latently infected cells, possibly leading to greater viral load. 