Bovine leukemia virus can be classified into seven genotypes: evidence for the existence of two novel clades

Abstract

Previous studies have classified the env sequences of bovine leukemia virus (BLV) provirus from different locations worldwide into between two and four genetic groupings. These different studies gave unique names to the identified groups and no study has yet integrated all the available sequences. Thus, we hypothesized that many of the different groups previously identified actually correspond to a limited group of genotypes that are unevenly distributed worldwide. To examine this hypothesis, we sequenced the env gene from 28 BLV field strains and compared these sequences to 46 env sequences that represent all the genetic groupings already identified. By using phylogenetic analyses, we recovered six clades, or genotypes, that we have called genotypes 1, 2, 3, 4, 5 and 6. Genotypes 1-5 have counterparts among the sequence groupings identified previously. One env sequence did not cluster with any of the others and was highly divergent when compared with the six genotypes identified here. Thus, an extra genotype, which we named 7, may exist. Similarity comparisons were highly congruent with phylogenetic analyses. Furthermore, our analyses confirmed the existence of geographical clusters. INTRODUCTIONBovine leukemia virus (BLV) is a member of the family Retroviridae belonging to the genus Deltaretrovirus. This genus also includes Simian T-lymphotropic virus 1, 2, 3 and 5 (STLV-1, -2, -3 and -5) and Human T-lymphotropic virus 1, 2, 3 and 4 (HTLV-1, -2, -3 and -4). have not yet been associated with any pathology, likely due to their recent identification and to the low number of isolates. Therefore, BLV is considered a model of HTLV-1 and -2 . BLV is recognized as the aetiological agent of enzootic bovine leukosis, a disease that results in significant economic losses for the worldwide cattle industry. The most conspicuous clinical manifestation of bovine leukosis, which only develops in a small fraction of infected animals, is the clonal expansion and local accumulation of B cells that results in the development of lymphoid tumours (lymphosarcoma, LS) (Gillet et al., 2007). The majority of infections are not associated with any clinical signs (AL), and in approximately 30 % of infected cattle, the virus causes a persistent lymphocytosis (PL) (Burny et al., 1987;Mirsky et al., 1996).Analyses of the BLV envelope (env) gene of isolates collected in multiple geographical locations demonstrated significant sequence conservation (Camargos et al., 2002(Camargos et al., , 2007Coulston et al., 1990). Nevertheless, up to seven BLV genotypes can be identified by RFLP analysis (Asfaw et al., 2005;Coulston et al., 1990;Fechner et al., 1997;Kettmann et al., 1981;Licursi et al., 2002). Furthermore, the env sequences of the BLV provirus from different locations worldwide have previously been classified into between two and four genetic groupings (Camargos et al., 2002(Camargos et al., , 2007Felmer et al., 2005;Hemmatzadeh, 2007;Licursi et al., 2003;Mamoun et al., 1990;Monti et al., 2005;Zhao & Buehring, 2007), with similar results...

Identification of a new genotype of bovine leukemia virus

“…In recent years, several authors have tried to classify BLV strains into groups, clusters, or genotypes [8,11,23,33]. Initial phylogenetic analysis conducted with a 519-nt fragment of the BLV env gp51-encoding gene of 32 foreign and six domestic BLVs resolved all of the previously identified genotypes and clustered all Croatian sequences in a separate clade, revealing a new genotype.…”

“…Up to seven BLV genotypes can be identified by RFLP analysis [1,10,20]. A recent phylogenetic study on the BLV env gene of strains from different parts of the world has allowed these viruses to be classified into seven genotypes [27,33]. More recently, a [24] has indicated that BLV can be classified into at least eight genotypes.…”

“…Strains in the tree are indicated by accession numbers and the country of isolation. Genotypes according to Rodriguez et al[33] are indicated by numbers at the right of the figure. BLV isolates from Croatia are shown in bold italics.…”

Genetic diversity of bovine leukemia virus worldwide

“…Argentine (Dube et al 2000;Licursi et al 2003;Monti et al 2005;Dube et al 2009;Rodriguez et al 2009), genotype-1,…”

Metabolismo oxidativo de leucócitos em animais infectados pelo Vírus da Leucemia Bovina

“…Compartilhando arranjo estrutural e genético com os deltaretrovírus humanos 2 , associados a leucemia de células T e linfoma em adultos, ambos desenvolvem doença crônica e proliferação das células-alvo envolvendo células e mediadores imunitários. No mundo, apenas alguns países conseguiram sua erradicação 3 . No Brasil, todavia, sua ocorrência vem sendo relatada em quase todos os Estados 4 .…”