Abstract
Viral infections are common clinical problems in aged individuals often affecting both mortality and morbidity. The pathogenic mechanisms of the various viruses are not universal in aged individuals, i.e. the clinical disease may be caused by the reactivation of a virus which has stayed in the body in a latent form, or alternatively, the virus is exogenous, derived from the environment. However, it is now evident, that this concept is too simple. Recent data have shown that in our body, even in the blood of healthy individuals, there are large amount of various viruses, which seem to live in balance with our immune defense mechanism (viral normal flora?). Moreover, there is now data suggesting that remnants of ancient retroviral infections in our genome can be activated and show virus-like activities. The possible significance of these findings in immunosenescence is discussed.