Bovine leukemia virus (BLV) causes enzootic bovine leukosis (EBL), the most common neoplastic disease in cattle worldwide. The first EBL outbreak in Egypt was reported in 1997. To date, there are few studies regarding BLV diagnosis using only serological detection and no studies investigating the distribution of BLV provirus, which is the retroviral genome integrated into the host genome, in Egypt. The genetic characteristics of Egyptian BLV strains are also unknown. Therefore, we aimed to detect BLV provirus and determine BLV genetic variability among dairy cattle in Egypt. We collected 270 blood samples of dairy cattle from 24 farms located in five provinces in Egypt. Out of the 270 samples, 58 (21.5%) were positive for BLV provirus. Phylogenetic analysis based on 18 420-bp selected sequences out of 50 isolates of the BLV env-gp51 gene demonstrated that Egyptian BLV isolates were clustered into genotype-1 and-4, among 11 genotypes detected worldwide. Furthermore, phylogenetic analysis and alignment of the 501-bp sequence of the env-gp51 gene revealed that at least six genetically different strains are present in Egypt. Genotype-1 isolates comprised four different strains (G1-a, G1-b, G1-c, and G1-d) and genotype-4 isolates included two different strains (G4-x and G4-y). Moreover, in one farm with 100% infection rate, we identified three isolates of G1-a strain, 35 isolates of G4-x strain, and two isolates of G4-y strain. Overall, this study provides the new report on molecular prevalence of BLV in Egypt and records the coexistence of BLV genotype-1 and-4 in Egyptian cattle.

牛白血病病毒（BLV）引起动物性牛白血病（EBL），这是全世界牛中最常见的肿瘤性疾病。埃及于1997年首次爆发EBL。迄今为止，很少有关于仅使用血清学检测进行BLV诊断的研究，而没有研究BLV前病毒（整合到宿主基因组中的逆转录病毒基因组）分布的研究。埃及BLV株的遗传特征也未知。因此，我们旨在检测BLV前病毒，并确定埃及奶牛中BLV的遗传变异性。我们从埃及五个省的24个农场收集了270头奶牛血样。在270个样本中，有58个（21.5％）的BLV前病毒呈阳性。系统进化分析基于BLV的50个分离株中的18 420-bp选定序列环保-gp51基因表明，在全世界检测到的11种基因型中，埃及BLV分离株聚类为基因型1和4。此外，该系统的501-bp序列的系统发育分析和比对环保gp51基因显示埃及至少存在6种遗传上不同的菌株。基因型1分离株包含四个不同的菌株（G1-a，G1-b，G1-c和G1-d），基因型4分离株包含两个不同的菌株（G4-x和G4-y）。此外，在一个感染率为100％的农场中，我们鉴定出3株G1-a菌株，35株G4-x菌株和2株G4-y菌株。总体而言，这项研究提供了有关埃及BLV分子流行的新报告，并记录了埃及牛中BLV基因型1和4的共存。