Genotyping bovine leukemia virus in dairy cattle of Heilongjiang, northeastern China

Abstract

Background: Bovine leukemia virus (BLV) causes enzootic bovine leukosis in cattle and leads to heavy economic losses in the husbandry industry. Heilongjiang Province, China, is rich in dairy cattle. However, its current BLV epidemiology and genotypes have still not been evaluated and confirmed. In this report, we investigated the BLV epidemiology in dairy cattle in the major regions of Heilongjiang Province via the nested PCR assay.

Results: A total of 730 blood samples were collected from nine different farms in six regions of Heilongjiang. The results showed that the infection rate of these regions ranged from null to 31%. With a clustering analysis of 60 published BLV env sequences, genotypes 1 and 6 were confirmed to be circulating in Heilongjiang. Importantly, a new genotype, 11, and a new subgenotype, 6E, were also identified in the Harbin and Daqing regions, respectively. An epitope analysis showed that a cluster of T-X-D-X-R-XXXX-A sequences in genotype 11 gp51 neutralizing domain 2 was unique among all currently known BLV isolates and was therefore a defining feature of this new genotype.

Conclusions: BLV epidemics and genotypes were initially investigated in dairy cattle of Heilongjiang. A relatively high infection rate was found in some regions of this province. A new genotype, G11, with a highly specific motif, was identified and thus added as a new member to the current BLV genotype family. This report provides an initial reference for future investigations and subsequent control of BLV transmission and spread in this region.

Keywords: Bovine leukemia virus; Cattle; Enzootic bovine leukosis; Genotyping.

Fig. 1

Map of dairy cattle distribution in China and HLJ Province territory. a Current dairy cattle distribution in China. Colors from light to dark indicate that the amounts of cattle gradually increased. Cattle amounts in the darkest region were more than 200,000, as in HLJ. b The map of HLJ Province territory. We collected samples from six major regions of HLJ. Each region is indicated with a black dot from left to right. Harbin is the capital of HLJ Province. Colors from light to dark indicate that the infection rate gradually increased. QQHR, Qiqihar; DQ, Daqing; SH, Suihua; HRB, Harbin; MDJ, Mudanjiang; JX, Jixi; and ND, not determined

Fig. 2

Polymorphism analysis of HLJ BLV isolates aligned with a Japanese strain, CAM69 (KJ668816.1). The sequences of our isolates were deposited in GenBank. The arrows indicate nonsynonymous nucleotide substitutions

Fig. 3

Deduced amino acid analysis of the 423-bp env gene of HLJ BLV isolates. The major epitope regions are shown. ND indicates the neutralizing domain. The ZB is also indicated

Fig. 4

Phylogenetic analysis of BLV env 423-bp nucleotide sequences from China and other countries. The phylogenetic tree was made using the maximum likelihood method. The ten known major genotypes are labeled G1 to G10. The new G11 and G6E are indicated as red circles and blue circles, respectively. HLJ BLV isolates were clustered into three genotypes, G1, G6, and G11