To the Editor.
—We report herein evidence of human foamy virus (HFV) infection in patients with familial Mediterranean fever (FMF) in Japan. Although HFV was the first identified human retrovirus, no definite relationship to a specific disease has been reported to date. Therefore, HFV has been characterized as "a virus in search of a disease." Human foamy virus protein is recognized to act as a superantigen, and HFV transgenic mice develop neurological abnormalities.1 Thus, we hypothesized that HFV might be one of the putative pathogens for sarcoidosis, idiopathic pulmonary fibrosis, or other pulmonary diseases, and surveyed for HFV gene elements in the genomic DNA of peripheral blood leukocytes or mRNA of bronchoalveolar lavage fluid cells of 320 patients with various lung diseases including sarcoidosis, idiopathic pulmonary fibrosis, lung cancer, and chronic obstructive pulmonary disease. Among them were three cases of FMF. The presence of HFV gene elements in genomic