Acyclovir-resistant herpes simplex virus causing pneumonia after marrow transplantation.

Three marrow transplant patients developed pneumonia due to acyclovir-resistant thymidine-kinase-deficient herpes simplex virus (HSV) type 1. In all three, pneumonia was evident at autopsy by both standard and immunohistology, and virus was recovered from culture of lung tissue. Two patients also had other pulmonary infections at death; one had only HSV pneumonia. All had received prophylaxis and repeated treatment courses with acyclovir, and all initially had acyclovir-sensitive virus. The acyclovir-resistant HSV strains were sensitive to foscarnet, and in at least one case to vidarabine, but as expected were resistant to ganciclovir. These cases represent potentially severe visceral infection in which acyclovir-resistant virus strains were primary or important copathogens. Although acyclovir-resistant HSV is generally considered less virulent, these cases illustrate the potential importance of infection due to acyclovir-resistant HSV in severely immunocompromised patients. They also highlight the need to test HSV strains for antiviral sensitivity and to consider alternative therapies to acyclovir in appropriate clinical situations.