Human Cytomegalovirus Infections in Immunosuppressed Patients
Not all virus infections are increased following organ transplantation. The most common are infections by the herpesvirus group, papovavirus (warts and BK virus), hepatitis viruses, and perhaps adenoviruses (Ho, 1977; Rubin and Young, 1988). Symptomatic infections are most commonly caused by herpesviruses and warts (Spencer and Andersen, 1979). Infection with many other common viruses such as rhinoviruses, myxovirus, paramyxoviruses, rubella, enteroviruses, and arboviruses do not appear to be greatly increased, although there are reports of infection with one or another. The exception may be bone marrow transplant recipients, who may develop adenovirus, rotavirus, coxsackievirus, and respiratory synctial virus infections (Townsend et al., 1982; Englund et al., 1988). This may be related to the suppression of humoral as well as cellular immunity in these patients. A virus may be transmitted from the outside and infect de novo either a seronegative “nonimmune” subject (primary infection) or a seropositive “immune” subject (reinfection). The virus may also arise from a latent site within a seropositive patient and be activated (reactivation infection). Reinfections and reactivation infections are also called “secondary infections.” Primary infections cannot occur if there is no opportunity for exposure to the agent or if preexisting natural or acquired immunity of the patient obviates the risk of exposure. Such immunity may remain operative to some extent despite immunosuppressive measures after transplantation, particularly humoral immunity.