Viral Infections in Immunocompromised Patients

In Chapter 8 we discussed the role of the various arms of the immune response in controlling viral infections, and in Chapter 10 the reactivation of persistent infections by immunosuppression. Table 10-6 listed the viruses commonly reactivated in immunocompromised patients.

In the context of this final overview of viral disease it is sufficient merely to add that reactivation of latent herpesviruses, in particular, has become commonplace as a result of three advances in modern medicine: (1) organ transplantation, requiring as it does, profound immunosuppression to prevent rejection of the allograft, (2) chemotherapy of cancer using highly cytotoxic drugs and/or radiotherapy, (3) rescue of children with profound congenital immunodeficiency syndromes who would not previously have lived. To these three iatrogenic changes should be added two major naturally occurring immunosuppressive diseases, AIDS and cancer (particularly lymphomas). The dangers are enhanced by the fact that the massive blood transfusions (or hemodialysis), so often an integral part of the life-saving therapeutic regime, carry the risk of iatrogenic transmission of exogenous viruses such as cytomegalovirus or Epstein-Barr virus, which may overwhelm a patient already desperately ill; the once considerable danger of transmitting HIV, hepatitis B, and hepatitis C in this way has almost disappeared as a result of the introduction of universal screening of blood, blood products, and organ donors (not yet completely for hepatitis C). Severely burnt patients are also highly vulnerable to invasion by herpes simplex viruses.

The magnitude of the problem is dramatically illustrated by the observation that it is quite standard for more than one, and sometimes all six, of the herpesviruses (HSV-1 and HSV-2, VZV, CMV, EBV, and HHV-6) to be reactivated in bone-marrow transplant recipients; in some series, up to 25% of all such patients have died of CMV pneumonia alone! Similarly, AIDS patients characteristically suffer the consequences of successive reactivation, sometimes in a roughly predictable order as their CD4+ T cell count drops, of any or all of the herpesviruses, plus polyomavirus, papillomaviruses, adenoviruses, and hepatitis B virus (see Chapter 35). The pathogenesis, clinical manifestations, and management of immunocompromised patients by antiviral chemotherapy, active or passive immunization, and appropriate vir-ologic and immunologic screening were discussed for each of the herpesviruses individually in Chapter 20; reactivation of human polyomaviruses was addressed in Chapter 18 and that of adenoviruses in Chapter 19.

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