Enzootic bovine leukosis (EBL) and recent prevalation and control measurement in Japan
2009
Murakami, K., National Inst. of Animal Health, Tsukuba, Ibaraki (Japan)
Enzootic bovine leukosis (EBL) is a disease of adult cattle caused by infection with a retrovirus, namely bovine leukaemia virus (BLV). BLV is classified into the genus Deltaretrovirus in the family Retroviridae. It is closely related to human T cell leukemia virus types 1 and 2 (HTLV-1 and -2). Approximately 30% of cattle infected with BLV have persistent lymphocytosis, and 1-5% develop B-cell lymphosarcoma. With a worldwide distribution, EBL is listed by the World Organization for Animal Health (OIE) as a disease of importance to international trade and is included in the national eradication program in Australia and some member states of the European Union (EU). EBL has been successfully eradicated from several EU countries: Belgium, Denmark, Germany, Spain, France, Ireland, Luxembourg etc. In contrast, 89% of dairy herds in the United States are reported to be infected with BLV, and the annual economic loss due to EBL is estimated at $525 million in decreased milk yield. Although EBL causes serious economic damage in the dairy industry, thus far only regional voluntary control programs have been implemented in the United States. In Japan, EBL is listed as a notifiable disease, but no nationwide control programs have been established yet. According to animal health statistics, EBL was reported in 159 cattle in 2000 and in 1,040 cattle in 2008. These data suggest that EBL is gradually spreading in Japan. In this review, the present situation of EBL in Japan is outlined with specific attention on virology, epidemiology, diagnosis, pathology and immunology, transmission of BLV and control of EBL.
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