Eduardo N. Esteban
National University of Central Buenos Aires (FCV-UNCPBA),Brasil
Title: Bovine Leukaemia Virus (BLV) true resistant cattle truncate virus transmission
Biography
Biography: Eduardo N. Esteban
Abstract
Economic losses in Argentina and particularly in subtropical regions are high due to BLV-induced leukaemia/lymphoma mortality plus reduction of milk production by BLV-infected cows. BLV-prevalence in the Departamento Rivadavia (Santiago del Estero Province) by 2011-2012 was 84.1% in dairy cattle. Facing such a high prevalence, controlling the virus by serological detection of BLV-infected cattle and culling from the herd is no longer an economically feasible option. No vaccine or therapeutic procedures to avoid BLV dissemination is available so far and controlled breeding of BLV-naturally resistant cattle selected by marker assistance rises as a unique tool to fight BLV. The effectiveness of this procedure depends on the premise that BLV-resistant cattle should not be an infection source for BLV-negative animals. Some BLV-infected animals develop the infection phenotype known as Low Proviral Load (LPL). The BLV-infection phenotypes are associated with the polymorphism of the bovine MHC Class II BoLA-DRB 3.2*. Allele BoLA-DRB3*0902 has the strongest association with LPL-phenotype. More than 80% of cattle selected by BoLA DRB3*0902 genotyping develop LPL when infected with BLV. To test under natural conditions whether these cattle break the BLV-transmission chain, selected BLV-infected LPL-BoLA-DRB3*0902 heterozygous cows were incorporated into a BLV-negative dairy herd. An average ratio of 5.4 (range 4.17-6.37) BLV-negative cows per BLV-infected cattle was kept during 20 months of experiment. Under the same conditions, non-characterized BLV-infected cows were mixed with BLV-negative animals to estimate the BLV-incidence rate (Irate) which was 0.0654%. Predicted BLV-prevalence for the entire region through 9 years using the estimated Irate was just slightly higher than observed BLV-prevalence. Instead, while the Irate predicted 20 new BLV-positive cattle after 20 months in contact with selected BLV-infected LPL-BoLA-DRB3*0902 animals, no BLV-negative cattle became infected. Conclusion. These results confirm for the first time that LPL-BoLA-DRB3*0902 cattle are indeed BLV-resistant and a feasible approach to control the virus.