Bovine Leukemia Virus (BLV) isolates genetic analysis in perinatally infected cattle at young age

Abstract

The purpose of the research is to identify perinatal infection in the dynamics, and assess the number and genetic status of bovine leukemia proviruses isolated from young animals, and correlations between some indicators of the infectious process based on gene diagnostics methods.Materials and methods. We used the material from cattle of different age groups: 1, calves (30–40 minutes after birth before colostrum and 15 to 45 days); and 2, heifers (not older than two years). Radial immunodiffusion (RID), real-time polymerase chain reaction (PCR), and phylogenetic analysis were used. Results and discussion. An assessment is given for perinatal infection of the young cattle. The detection rate of the infection in the calves was 4.15% (PCR) and 1.09% (RID); and 1.1% (PCR) and 0.88% (RID) in the heifers. A 36-fold decrease of the infection was found in positive dynamics (2013–2022) from 14.5 to 0.4% with passing through 0% (2020) and being at the level of 0% (2022). The proviral load ranged from 2.02 × 104 to 8.38 × 106 GE/mL in the blood of the examined animals. The BLV isolates obtained were shown to belong to two genotypes, GIV and GVII (env), and clade 1 (pol). We assessed an overestimation of the number of the proviruses by a factor of three in the animals under two years of age (3.83 × 106GE/mL) relative to that in the 1-month-old calves (1.3 × 106 GE/mL), and by a factor of nine for GIV relative to GVII. It is important to develop gene diagnostics algorithms to increase the effectiveness of routine tools to prevent the spread of this retrovirus infection in young animals at an early stage, which is confirmed by a decrease to 0% of detected retrovirus infection in young animals over time. The provirus number was higher in the heifers than the calves; the proviral load level was higher in the multiparous dairy cows than the nulliparous animals, and quantitative indicators were higher in the animals’ blood with the GIV genotype relative to those with the GVII genetic variant of the BLV.