Nakamura Laboratory, Baton Zone Program, RIKEN Cluster for Science, Technology and Innovation Hub, Wako, Saitama, Japan.
Department of Pathology and Microbiology, University of Veterinary Science, Yezin, Nay Pyi Taw, Myanmar.
PLoS One. 2020 Feb 21;15(2):e0229126. doi: 10.1371/journal.pone.0229126. eCollection 2020.
Bovine leukemia virus (BLV) is the etiological agent of enzootic bovine leukosis, which is the most common neoplastic disease of cattle. BLV infects cattle worldwide and causes serious problems for the cattle industry. In this study, we examined the prevalence of BLV infection and the distribution of BLV genotypes in cattle in the northern, central, and southern parts of Myanmar. The prevalence of BLV infection among Myanmar cattle (37.04%) in this study was markedly higher than the prevalence (9.1%) observed in our earlier study in which BLV was detected from the limited number of cattle only from a small area of Myanmar. Phylogenetic analysis of partial env-gp51 sequence of the isolated BLV strains revealed that there are at least three BLV genotypes (genotype-1, genotype-6, and genotype-10) in Myanmar, which have also been detected in the neighboring countries. We performed this study to estimate the BLV proviral load, which is a major diagnosis index for determining the virus transmission risk. The cattle of the three test regions with warm, wet, and humid climatic conditions (upper Sagaing, Yangon, and Kayin) exhibited a high mean proviral load, while cattle of three other regions with low annual rainfall and very high temperature (Mandalay, Magway, and upper Bago) exhibited a low mean proviral load. Further, the level of proviral load and the prevalence of BLV infection in Myanmar native cattle (N = 235) were lower than that in the hybrid cattle (Holstein Friesian × Myanmar native) (N = 62). We also observed that the cattle with high risk for BLV transmission, which have high proviral load, may enhance the BLV infection rate. Hence, to control BLV transmission, it is necessary to eliminate these cattle with high-risk for BLV transmission and to diagnose BLV provirus in cattle in the remaining regions/states of Myanmar sharing a boundary with neighboring countries.
牛白血病病毒 (BLV) 是地方性牛白血病的病原体，这是牛最常见的肿瘤性疾病。BLV 感染全世界的牛，并给牛养殖业带来严重问题。在本研究中，我们检查了缅甸北部、中部和南部地区牛 BLV 感染的流行率和 BLV 基因型分布。本研究中缅甸牛 BLV 感染的流行率（37.04%）明显高于我们之前的研究（仅从缅甸小面积的有限数量的牛中检测到 BLV，流行率为 9.1%）。从分离的 BLV 株的部分 env-gp51 序列进行的系统进化分析表明，缅甸至少存在三种 BLV 基因型（基因型-1、基因型-6 和基因型-10），这些基因型也在邻国中检测到。我们进行这项研究是为了估计 BLV 前病毒载量，这是确定病毒传播风险的主要诊断指标。在上萨高、仰光和克钦等三个气候温暖、潮湿和湿润的测试地区的牛表现出较高的平均前病毒载量，而在年降雨量和温度非常低的三个其他地区（曼德勒、马圭和上勃固）的牛表现出较低的平均前病毒载量。此外，缅甸本地牛（N=235）的前病毒载量水平和 BLV 感染率低于荷斯坦弗里生牛与缅甸本地牛的杂交牛（N=62）。我们还观察到，具有高 BLV 传播风险、高前病毒载量的牛可能会增加 BLV 感染率。因此，为了控制 BLV 传播，有必要消除这些具有高 BLV 传播风险的牛，并对与邻国接壤的缅甸其余地区/邦的牛进行 BLV 前病毒诊断。
