engleski

Phylogenetic analysis of Croatian Bovine Leukemia virus strains confirms the existence of the genotype 7 and the new genotype 8

Bovine leukemia virus (BLV) infection of cattle has been present continuously in some parts of Croatia for more than ten years although several European countries have successfully eradicated the infection. To investigate the degree of genetic variability of BLV strains circulating in Croatia, isolates from the largest dairy farms together with those from small family farms were examined by PCR for a segment of the gp51 env gene, followed by DNA sequencing and phylogenetic analysis. Two phylogenetic models were used, the Tamura-Nei for Neighbour-Joining analysis and General-Time-Reversible + Gamma model for Bayesian inference analysis. The nucleotide sequences were compared with other previously characterized BLV strains from different geographical areas, comprising all known BLV genotypes. Croatian isolates did not clustered with any of genotype characteristic for European isolates but reveal six to eight nucleotide substitutions with two amino acid changes. All isolates from largest diary farms clustered separately from the other sequences, revealing a new genotype as published recently (Balic et al., 2012). But, interestingly, not all of the isolates from small family farms clustered with the new genotype, preliminary nominated as genotype 8. The four of them clustered into genotype 7, a genotype which for the three decades was comprised of only one strain, the S83530 isolate from Italy and recently with three Chilean isolates. Croatian Genotype 7 isolates had three nucleotide changes common with the Italian isolate, but without the influence on the aminoacid level. The results showed that delayed BLV eradication and control programme in Croatia led to virus adaptation by mutating some parts of its genome, which resulted in enough divergence to form a new genotype.

bovine leukemia virus

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