Viruses and the immunocompromised

Individuals with natural or artificially induced immunosuppression are at risk of more severe clinical disease from a range of viral infections. For example, infants with the genetic disorder severe combined immunodeficiency (SCID) develop recurrent infections early in life (e.g. rotavirus in the gut, which induces prolonged diarrhea). In particular the Herpesviridae (such as HSV, CMV, and VZV), which are responsible for latent infections, show far more frequent reactivation and recurrence and severe recrudescence in immunocompromised individuals. Immune suppression is induced by medication following transplant surgery and may lead to generalized shingles (recurrence of VZV), CMV pneumonia or genital warts (HPV). Individuals with little or no antibody production (hypogammaglobulinemia) often harbor and excrete viruses for many years (e.g. poliovirus from the gut).

Some viruses induce immunosuppression in various ways, and to various levels.  For example, HBV suppresses the  induction of  interferon in  some hosts (which in  turn reduces  the   CTL  response),  while   the   measles  virus   transiently  suppresses  T-cell responses during replication. Severe immunosuppression results from HIV infection of CD4 T-helper cells and macrophages. The virus persists in the host for months or years, eventually progressing to high levels of replication within CD4 cells, seriously depleting the T-helper cell population. This results in serious immunosuppression (acquired immunodeficiency syndrome, AIDS) and susceptibility to a wide range of pathogens (that normally are readily eliminated by the immunocompetent host), which are usually the cause of death in such patients.