Enzootic Bovine Leukosis and It’s Eradication Measures

Abstract

Enzootic Bovine leukosis (EBL) is an infectious disease caused by the bovine leukemia virus (BLV) and is an important livestock infectious disease of international concern. In Japan, it is designated as a notifiable infectious disease, and the economic damage is also serious. While many infected cows show no symptoms, approximately 30% show persistent lymphocytosis (PL), and a few percent develop EBL. There are two transmission routes: horizontal and vertical. In recent years, the infection rate has been rising rapidly in Japan, and there is particular concern about the onset of EBL in fattening cattle aged around 30 months.

In terms of BLV eradication measures, a highly sensitive quantitative PCR method was developed between 2006 and 2008 under contract from the Ministry of Agriculture, Forestry and Fisheries. This method has made it possible to implement ‘high-level BLV-infected cattle detection-type’ eradication measures using the amount of provirus as an indicator. Furthermore, with support from the JRA Livestock Industry Promotion, research and development was carried out on (1) a model for detecting and isolating highly infected cattle, (2) a model for establishing an infected calf rearing center, and (3) a comprehensive model that uses a regional BLV testing center and an infected calf rearing center in combination.

Future issues for BLV eradication measures include measures to deal with vertical transmission, particularly BLV-infected calves born from infected mother. In addition, the need for coordinated efforts across the entire region and the issue of cost-sharing to ensure the sustainability of eradication measures are also important. The resolution of these issues will be the next step towards BLV eradication.