Detection and molecular characterization of bovine leukemia virus in various regions of Iran

Bovine Leukaemia Virus: Current Epidemiological Circumstance and Future Prospective

Bovine leukaemia virus (BLV) is a deltaretrovirus that is closely related to human T-cell leukaemia virus types 1 and 2 (HTLV-1 and -2). It causes enzootic bovine leukosis (EBL), which is the most important neoplastic disease in cattle. Most BLV-infected cattle are asymptomatic, which potentiates extremely high shedding rates of the virus in many cattle populations. Approximately 30% of them show persistent lymphocytosis that has various clinical outcomes; only a small proportion of animals (less than 5%) exhibit signs of EBL. BLV causes major economic losses in the cattle industry, especially in dairy farms. Direct costs are due to a decrease in animal productivity and in cow longevity; indirect costs are caused by restrictions that are placed on the import of animals and animal products from infected areas. Most European regions have implemented an efficient eradication programme, yet BLV prevalence remains high worldwide. Control of the disease is not feasible because there is no effective vaccine against it. Therefore, detection and early diagnosis of the disease are essential in order to diminish its spreading and the economic losses it causes. This review comprises an overview of bovine leukosis, which highlights the epidemiology of the disease, diagnostic tests that are used and effective control strategies.

Genetic analysis of the pX region of bovine leukemia virus genotype 1 in Holstein Friesian cattle with different stages of infection

The pX genetic region of bovine leukemia virus (BLV) includes four genes with overlapping reading frames that code for the Tax, Rex, R3, and G4 proteins. These proteins are involved in the regulation of transcriptional and post-transcriptional viral expression, as well as having oncogenic potential. Our goal was to investigate the pathogenicity of the pX region of BLV genotype 1 in terms of lymphocytosis, lymphomas, and proviral DNA load. We screened 724 serological samples from mixed-age Holstein Friesian cattle from six states in Mexico. Peripheral blood leukocytes (PBLs) were isolated from whole blood with anticoagulant, and genomic DNA was extracted from the PBLs using a commercial kit. Then, a set of primers that hybridize in conserved regions of the BLV pX region were used, which allowed for PCR standardization to detect proviral DNA in infected cells. Positive amplicons were sequenced using the Sanger method, resulting in 1156-nucleotide-long final sequences that included the four pX region genes. The experimental group consisted of 30 animals. Twelve of these had lymphocytosis, six had lymphoma, and 12 were apparently healthy cattle without any signs of lymphocytosis or lymphoma. The presence of lymphoma was detected in six bovine tumor tissues using histopathology, and the presence of BLV was detected by in situ hybridization. Phylogenetic analysis demonstrated that the 30 sequences were associated with genotype 1, and the genetic distance between the sequences ranged from 0.2% to 2.09%. We identified two sequences in the G4 gene: one with a three-nucleotide deletion resulting in the loss of a leucine (AGU_7488L, in a cow with lymphocytosis), and one with a nine-nucleotide deletion resulting in the loss of leucine, proline, and leucine (AGU_18A, in a cow without lymphocytosis). Analysis of the PX region indicated that positive selection had occurred in the G4, rex, and R3 genes, and we found no difference in proviral DNA load between the studied groups. We were unable to establish an association between variations in the pX region and the development of lymphocytosis, lymphoma, asymptomatic status, or proviral DNA load in BLV-infected cattle.

Seroprevalence, Risk Factors and Molecular Identification of Bovine Leukemia Virus in Egyptian Cattle

Simple Summary

Bovine leukemia virus (BLV) is distributed worldwide and affects dairy cattle causing significant economic losses. This study’s objective was to assess the risk factors associated with BLV infection and identify the Egyptian BLV strain’s genetic diversity. The overall seroprevalence of BLV infection in Egyptian dairy cattle was 18.2%, and the grazing cattle in the losing house system had a higher probability of getting BLV infection. The sequencing and phylogenetic analysis for one Egyptian BLV strain was performed, and the obtained results confirmed the clustering of Egyptian BLV strain into genotype-1.

Abstract

Bovine leukemia virus (BLV) is distributed worldwide and affects dairy cattle causing severe economic losses. The BLV has been serologically reported in Egypt, but few studies have evaluated its associated risk factors and genetic classification. Therefore, this study assessed risk factors associated with BLV infection and identified the genetic diversity of the Egyptian strain. The study was conducted on 500 dairy cattle distributed in four Governorates located in Northern Egypt. Overall, the seroprevalence of BLV infection among Egyptian dairy cattle was 18.2%. The grazing cattle in the losing house system had higher odds for BLV seropositivity, and bad practice such as the use of a single needle or one plastic glove for more than one animal was considered a significant risk factor for BLV infection. Besides, the sequencing and phylogenetic analysis for one Egyptian BLV strain was performed, and the obtained results confirmed the clustering of Egyptian BLV strain into genotype-1. The assessment of associated risk factors for BLV infection and determination of its genetic classification are essential to implement an effective control program.