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.

Phylogenetic analysis based on whole genome sequence of bovine leukemia virus in cattle under 3 years old with enzootic bovine leukosis

“…Although almost all BLV-infected animals remain clinically asymptomatic throughout their lifespan, less than 5% of the infected cattle develop EBL [ 2 ]. Due to the lengthy latency period required by BLV, EBL is commonly seen in cattle older than 3 years [ 3 ], while onset of EBL in cattle under 3 years old has also been observed in Japan [ 4 – 6 ]. Although some factors related to onset of EBL in young cattle have been reported [ 6 – 8 ], the mechanism of early EBL onset is not fully understood.…”

“…Because proviral and disease progression were positively correlated, the pathogenicity might be different among groups. In addition, a case of EBL caused by BLV classified as group A in young cattle has been reported [ 6 ]. However, the relationship between early onset of EBL and BLV groups has been unclear.…”

“…Although almost all BLV-infected animals remain clinically asymptomatic throughout their lifespan, less than 5% of the infected cattle develop EBL [2]. Due to the lengthy latency period required by BLV, EBL is commonly seen in cattle older than 3 years [3], while onset of EBL in cattle under 3 years old has also been observed in Japan [4][5][6]. Although some factors related to onset of EBL in young cattle have been reported [6][7][8], the mechanism of early EBL onset is not fully understood.…”

Enzootic bovine leukosis caused by bovine leukemia virus classified as Group C based on viral whole genome sequencing in a 23-month-old Holstein-Friesian heifer

“…Enzootic bovine leukosis (EBL) is a B-cell lymphoma caused by bovine leukemia virus (BLV) in cattle older than 3 years of age [ 1 ], although early-onset EBL in cattle under 3 years of age has also been reported [ 7 , 12 ]. Enlargement of superficial lymph nodes and masses in the pelvic cavity are important clinical findings that can lead to a suspicion of EBL [ 1 , 2 ].…”

“…BLV in EBL cattle under 3 years of age is mainly classified as Group A or B-1 [ 5 , 11 ], and previous studies have reported no Group C strain in EBL cattle. In fact, Group C BLV has only been isolated from cattle without EBL [ 5 , 7 , 11 ]. Here we report a clinical case of EBL caused by BLV classified as Group C in a 23-month-old Holstein-Friesian heifer with no enlargement of lymph nodes or masses in the pelvic cavity.…”