Enzootic bovine leukosis in a 21-month-old Japanese Black cow with high susceptibility

Abstract

A 21-mo-old Japanese Black beef cow had swollen mandibular and superficial cervical lymph nodes. Fine-needle aspiration cytology of the superficial cervical lymph node revealed large lymphoblasts with mitoses present. The bovine leukemia virus (BLV) proviral load was relatively high, and phylogenetic analysis of the whole BLV genome classified the BLV strain as one with high viral replication activity. Genotyping of bovine leukocyte antigen genes indicated that the cow was susceptible to enzootic bovine leukosis (EBL). The bone morphogenetic protein 6 (BMP6) gene promoter region was hypermethylated. Monoclonal proliferation of B cells and monoclonal integration of the BLV provirus in the bovine genome were detected by a clonality test of B cells and an inverse PCR assay, respectively. At autopsy, generalized swelling of lymph nodes and spinal canal invasion by tumor tissue at vertebrae L5-6 were observed. Histologic analysis revealed diffuse proliferation of large round neoplastic cells that were positive for BLA36 and negative for CD3. The cow was definitively diagnosed with EBL based on these findings. Infection with a highly pathogenic strain of BLV, susceptibility of the BoLA-DRB3 alleles, and hypermethylation of the BMP6 gene may have contributed to the development of EBL in our case.

Keywords: BoLA; Japan; bovine leukemia virus; cattle; enzootic bovine leukosis; methylation.

Figure 1.

Swelling of parotid (arrow) and prescapular (arrowhead) lymph nodes on day 12 in a Japanese Black cow with enzootic bovine leukosis.

Figure 2.

Phylogenetic analysis of the whole bovine leukemia virus (BLV) genome sequence in our case. A maximum-likelihood phylogenetic tree was constructed from whole BLV genome sequences of our case and 28 reference sequences. The BLV strains were divided into A–C based on a previous study. The bar denotes distance.

Figure 3.

Histopathology and immunohistochemistry of superficial lymph node. Neoplastic cells had a round nucleus with nuclear atypia and granular patterned chromatin. These cells stained positive for BLA36 and negative for CD3. A. H&E. B. BLA36 and C. CD3 with Mayer hematoxylin counterstain. Bars = 20 μm.