Progressive immunodeficiency and fatal pneumonitis associated with human herpesvirus 6 infection in an infant.

Human herpesvirus 6 (HHV-6), an important opportunistic pathogen in immunocompromised patients, causes fatal pneumonitis, encephalitis, and bone marrow suppression. Its ability to infect and destroy T lymphocytes may allow it to synergize with the human immunodeficiency virus in the destruction of lymphoid tissues in patients with AIDS. We describe herein an infant who had an immunodeficiency associated with thymic atrophy and severe T lymphocytopenia who developed fatal pneumonitis due to HHV-6. Dense and disseminated infection of T lymphocytes with HHV-6 was also documented. In the absence of any other documented cause of immunodeficiency, we hypothesize that congenital infection of this infant with HHV-6 may have caused progressive destruction of her cellular immune system, leading to the fatal pneumonitis. Thus, HHV-6 infection may have been the cause of both her immunodeficiency and her fatal opportunistic infection.