ABSTRACT. A disease characterized by papules, nodules, vesicles and, rarely, pustules and ulcers on teats was seen among cattle on a farm in Chiba Prefecture, Japan. A virus was isolated by inoculation of fetal bovine lung cell cultures from a vesicle on a teat of an infected cow. The virus was subsequently passaged in fetal bovine lung and muscle cells in which it produced complete cytopathic changes. The virus was identified by physicochemical examinations and electromicroscopic observation as a parapoxvirus. A seroepidemiological survey was performed on antibody to the isolated virus by the agar gel immunodiffusion test. The isolated virus formed a precipitation line which cross reacted with other parapoxviruses isolated previously in Japan. The positive rate was more than 50% among cattle in the Kanto district. The positive rate increased with age. It was suggested that parapoxvirus infection might have already been prevalent among cattle in Japan.-KEY WORDS: cattle, dermatitis, mammilitis, papula, parapoxvirus.J. Vet. Med. Sci. 61 (7): [749][750][751][752][753] 1999 48 hr and fresh medium was added. The cells were cultivated again for at least 12 days. The inoculated cell cultures were freeze-thawed three times and inoculated onto fresh FBL cells if a cytopathic effect (CPE) was not observed. The blind passage was repeated twice.Control viruses: Four strains of parapoxvirus isolated previously in Japan and vaccinia virus were used as controls for serological tests. The Aomori and Iwate strains were isolated from a cow with bovine papular stomatitis and a sheep with contagious pustular dermatitis, respectively, and preserved in the National Institute of Animal Health [7]. The Ishikawa-B strain and the Ishikawa-S strain were isolated from a cow and a Japanese serow with papular stomatitis, respectively, and kindly supplied by the Nanbu Livestock Hygiene Service Center in Ishikawa Prefecture. Vaccinia virus (Lc16mO strain), bovine herpesvirus type 1 (Los Angeles strain) and bovine viral diarrhea virus (Nose strain) were preserved in the National Institute of Animal Health [4,5,15]. All viruses were propagated in fetal bovine muscle (FBM) cells.Cell cultures: FBL cell cultures and FBM cell cultures were prepared by an original tissue-culture method. FBL cells were used within 5 passages for virus isolation and FBM cells were within 20 passages for physicochemical examinations of the isolated virus and viral antigen preparation. MDBK cells were employed for antigen preparation of the isolated virus for the agarose gel immunodiffusion (AGID) test. These cells were cultivated at 37°C in Eagle's MEM containing 5% fetal calf serum and 0.3% tryptose phosphate broth.Electron microscopic observation: Culture fluids collected from FBM cells infected with the isolated virus and induced CPE were centrifuged for 30 min at 10,000 g. The supernatant was then centrifuged for 2 hr at 110,000 g.