Molecular Characterization of Bovine Leukaemia Virus (BLV) Strains Reveals Existence of Genotype 6 in Cattle in India with evidence of a new subgenotype

Abstract

Bovine leukaemia virus (BLV) causes enzootic leucosis in cattle and is prevalent worldwide. Although recent studies have shown that BLV strains can be classified into 10 distinct genotypes, no information is available regarding the BLV genotype prevalent in cattle in India. To determine the genetic variability in BLV, in this study, 118 adult dairy cows from three states of India were screened for BLV infection by env gp51-specific ELISA and nested PCR. Of the 33 cows found positive by both PCR and ELISA, 10 selected BLV strains were subjected to molecular characterization. Phylogenetic analyses of partial and full-length env gp51 gene sequences of Indian BLV strains and other geographical diverse BLV strains representing all the 10 genotypes revealed that Indian strains belonged to BLV genotype 6. Although Indian strains showed close genetic proximity with the strains circulating in South America, they were classified into a new subgenotype within genotype 6. Alignment of deduced amino acid sequences in gp51 demonstrated substitutions mainly in conformational epitope G, neutralizing domain 2 and linear epitope D, with a novel mutation (threonine to alanine at residue 252) found in D-epitope of all the Indian BLV strains. Although serological evidence of BLV infection in India has been reported earlier, this study on molecular characterization of BLV strains established the existence of BLV genotype 6 in India. Additionally, the results of this study highlight the importance of genetic analysis of geographically diverse BLV strains to understand BLV global genetic diversity and further studies are required to determine BLV genetic diversity and extent of BLV infection in cattle in India.

Detection and Molecular Characterization of Bovine Leukemia Virus in Egyptian Dairy Cattle

“…Likewise, BLV infection rate reported in some of the neighboring countries include 20.2% in Saudi Arabia ( 42 ) 7.75% in Iraq ( 44 ), despite being high (48.3% in herd level) in Turkey ( 39 ). In contrast, the BLV infection rate among cattle of Egypt reported in this study was close to or lower than that in India (27.9%) ( 45 ). However, the BLV infection rate reported here compared with that reported in some other Asian countries was being higher than that reported in Philippines (4.8–9.7%) ( 29 ) and markedly lower that in Japan (40.9%) ( 46 ), Korea (42.16%) ( 47 ), and Myanmar (37.04) ( 36 ).…”

Detection and genotyping of bovine leukemia virus (BLV) in Vietnamese cattle

“…Phylogenetic analysis of the partial or complete sequence of the env-gp51 gene indicated the existence of six subgenotypes or subgroups within BLV genotype 6: G6a, G6b, G6c [ 32 ], G6d, G6e [ 13 , 20 ], and a recently designated subgenotype G6f [ 9 , 43 ]. Two Vietnamese BLV isolates (LC512450, LC512451) from the present research were clustered into subgroup G6f with the reported subgenotype G6f strains (GenBank accession numbers: KU764766, KU764759, KU764749 and MF817721) identified in the recent studies of Vietnam and China [ 9 , 43 ].…”

Molecular Characterization of the env Gene of Bovine Leukemia Virus in Cattle from Pakistan with NGS-Based Evidence of Virus Heterogeneity

“…The main reason for this was the consideration of too short fragments of the env gene in the phylogenetic tree. Indeed, the classification of sequences to a specific subgenotype depends on the fragment that was analyzed [30,42].…”

“…Since phylogenetic analysis based on 903 bp fragments provided the data on the existence of at least two subgenotypes within genotype G6, we attempted to classify possible subgenotypes in the G6 genotype by taking into account all the sequences known to date to be affiliated with this genotype. However, we found some inconsistency in classification of several sequences to a particular subgenotype of G6 in recently published data [30,42,43]. Most of sequences available from GeneBank and affiliated so far with genotype G6, had lengths shorter than 903 bp; therefore, this analysis included sequences of 501 bp length, which were previously used in other studies [43,44].…”