Sporadic acute hepatitis E of a 47-year-old man whose pet cat was positive for antibody to hepatitis E virus.

We encountered a patient with sporadic acute hepatitis E who had not traveled to areas endemic for hepatitis E virus (HEV) infection and may have been infected in Japan. The patient was a 47-year-old male who had no history of blood transfusion or contact with travelers to hepatitis E-endemic regions or unspecified individuals. The disease presented with general malaise, fever, and brown urine as chief complaints in April 2002. Various hepatitis virus markers were negative, but IgM class antibodies to hepatitis E virus (anti-HEV) and HEV RNA were positive, and the patient was diagnosed with acute hepatitis E. The entire nucleotide sequence (7240 bases) of HEV (HE-JK4) isolated from this patient was determined and compared with known HEV strains. HE-JK4 belonged to genotype IV and exhibited higher similarities to genotype IV HEV strains previously isolated in Japan than to those isolated in China, Taiwan, and Vietnam. The patient's family members living with him were negative for anti-HEV IgG and IgM, but their pet cat was anti-HEV IgG-positive. This finding suggests a potential route of infection of sporadic cases of hepatitis E in Japan. Since the presence of HEV indigenous to Japan is predicted, HEV infection should be considered in the diagnosis of acute hepatitis of unknown cause, even for patients who have not traveled abroad.