Bovine Leukemia Virus Ribozymes

Bovine leukemia virus (BLV) is a retrovirus structurally related to human T-cell leukemia virus-I and -II and simian T-cell leukemia virus. It infects principally B-lymphocytes (1 ), causing a persistent expansion of B-cells, termed persistent lymphocytosis, in approx 30% of infected cattle; about 5–10% of these animals eventually progress to leukemia or lymphoma (2 ). The disease is common in the United States, where economic losses as a result of the condemnation of carcasses with lymphoma cause an annual estimated loss of $44 million (3 ) and reduced milk and milkfat production in lactating cows with persistent lymphocytosis causes another $42 million annual loss (4 ,5 ). Loss of trade to countries which prohibit importation of BLV infected cattle is also a significant loss (3 ).