Bovine Leukemia Virus Research Articles

In 2017, the Commission Implementing Decision (European Union [EU]) 2017/1910 officially declared Italy to be enzootic bovine leukosis (EBL)-free. The Commission Delegated Regulation (EU) 2020/689 laid criteria to maintain an official disease-free status. While some infection clusters persist in restricted areas, specific measures are being implemented to eliminate pockets of viral persistence. This updated analysis of current data, concerning epidemiological trends of EBL in Italy from January 2022 to December 2024, aimed to analyze the status of infection clusters in terms of risk factors associated with bovine leukemia virus (BLV) seropositivity to evaluate the effectiveness of the eradication measures. Our findings highlighted an improvement in EBL eradication; however, the Latium region lags behind in terms of disease eradication while the situation in Apulia is being resolved. Campania, which has implemented restrictive and consistent health measures, has the lowest prevalence and incidence rates compared with previous years. Identifying and assessing risk factors that favor EBL persistence in infection clusters is essential as is implementing specific measures to eliminate such clusters, thereby enabling disease eradication and the adoption of targeted prevention strategies.

The effect of bovine leukemia virus infection on health and growth of nonreplacement dairy calves.

BackgroundBovine leukemia virus (BLV) is an oncogenic deltaretrovirus that induces enzootic bovine leukosis. A defining feature of BLV is its viral miRNA cluster, which is transcribed atypically by RNA polymerase III via internal type 2 promoters rather than through the canonical Pol II pathway. These miRNAs accumulate to high levels within infected lymphocytes and can alter expression of a variety of host genes involved in lymphocyte proliferation and impose leukemogenic processes.ResultsHere, we present a comprehensive in silico characterization of new A-box and B-box promoter motifs within the BLV miRNA-coding region. As the first step, a taxonomically diverse dataset of small non-coding RNAs (tRNAs, SINEs, and other ncRNAs) was assembled to derive position-weight matrices and corresponding IUPAC consensus sequences for type 2 internal Pol III promoter motifs. Using these models, all available BLV miRNA cluster sequences were scanned to identify and map A-box-like and B-box-like elements and to reconstruct the underlying promoter architecture. Our analyses reveal a noncanonical BLV promoter organization: overlapping degenerate A-box variants—most frequently three distinct elements—reside within the pre-miRNA hairpin region, whereas B-box elements were positioned downstream of the Pol III termination signal, effectively excluded from the mature transcript.ConclusionsDespite motif degeneration, critical nucleotide positions remained strongly conserved, indicating evolutionary pressure to preserve Pol III recruitment while accommodating viral genome constraints. These findings fill a crucial gap in understanding of BLV Pol III promoter architecture and provide a foundation for future studies on how unconventional promoter configurations regulate viral miRNA expression and virus–host interactions.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12864-025-12074-y.

Bovine leukemia virus (BLV), an oncogenic retrovirus of the genus Deltaretrovirus, causes enzootic bovine leukosis (EBL), the most prevalent neoplastic disease in cattle and a major source of economic loss. While BLV prevalence has been studied in commercial breeds, data on native Latin American cattle remain limited. This study assessed BLV infection and proviral load in 244 animals from six native breeds: Argentine Creole (CrAr), Patagonian Argentine Creole (CrArPat), Pampa Chaqueño Creole (CrPaCh), Bolivian Creole from Cochabamba (CrCoch), Saavedreño Creole (CrSaa), and Siboney (Sib), sampled across Argentina, Bolivia, Paraguay, and Cuba. BLV-CoCoMo-qPCR-2 assay detected BLV provirus in 76 animals (31.1%), with a mean load of 9923 copies per 105 cells (range: 1–79,740). Infection rates varied significantly by breed (9.8% in CrAr to 83.8% in CrPaCh) and country (15.6% in Argentina to 83.8% in Paraguay) (p = 9.999 × 10−5). Among positives, 57.9% exhibited low proviral load (≤1000 copies), and 13.2% showed moderate levels (1001–9999), suggesting potential resistance to EBL progression. This is the first comprehensive report of BLV proviral load in Creole cattle across Latin America, offering novel epidemiological insights and highlighting the importance of native breeds in BLV surveillance.

The article presents up-to-date information on the etiology, epizootiology, and pathogenesis of bovine leukemia virus (BLV). The structure and functions of the main viral genes are considered, with emphasis on their role in replication, integration into the host genome, and the formation of persistent infection. Particular attention is paid to the regulatory proteins Tax and Rex, which play a crucial role in viral persistence and tumor development. The main routes of virus transmission are described, including horizontal, vertical, and iatrogenic pathways, as well as clinical manifestations such as asymptomatic infection, persistent lymphocytosis, and tumor form (lymphosarcoma). Data on the spread of BLV in Kazakhstan from its first registration to the present are summarized, and the dynamics of the epizootic situation across different regions of the country are analyzed. It is emphasized that the virus continues to circulate in several areas, which necessitates enhanced monitoring, the application of molecular diagnostic methods, and the development of comprehensive preventive measures. In addition, the scientific analysis of the article examines the economic consequences of bovine leukemia virus for farms, including decreased milk productivity, herd reduction, limited export potential, and expenses for veterinary and sanitary measures.

Effect of colostrum replacer containing bovine leukemia virus antibodies on infection and antibody level in young calves

Relationship between bovine leukemia virus (BLV) infection and shedding provirus from milk in cows.

Vultures have suffered a drastic population decline mainly due to poisoning and traumatic lesions; neoplastic diseases in these birds are rarely documented. Here we describe the clinical and pathologic findings of lymphoma in 2 free-ranging black vultures (Coragyps atratus). Upon initial evaluation, both birds were severely emaciated; vulture 1 had proptosis of the right eye and vulture 2 swelling of the left wing. The vultures died shortly after presentation and were autopsied. In both birds, the thymus and many other organs were expanded by poorly demarcated, white, soft masses that were composed histologically of proliferating lymphocytes of monomorphic appearance. In vulture 2, thickening of the left-wing bones appeared to be caused by periosteal reaction, associated with bone invasion by the same type of lymphocytes, and granulomatous osteomyelitis. By immunohistochemistry, neoplastic cells were reactive for CD3 and negative for PAX5. The final diagnoses were multicentric T-cell lymphoma. PCR assays for Marek disease, avian leukosis, reticuloendotheliosis, and bovine leukemia viruses were negative in both cases. To our knowledge, lymphoma has not been reported previously in vultures.

The bovine leukemia virus (BLV) and bovine foamy virus (BFV) are retroviruses that encode microRNAs (miRNAs) and infect cattle. While the role of BFV-derived miRNAs remains unclear, BLV miRNAs have gained attention for their potential involvement in oncogenesis. BLV-BFV co-infections are common, and given foamy viruses' potential to cross species barriers, it is essential to prevent their presence in the food chain. We reported the co-expression of three BFV-derived miRNAs and seven BLV-derived miRNAs in naturally infected cattle. A protein-protein interaction graph analysis of genes targeted by viral and host-derived miRNAs revealed key metabolic pathways associated with tumorigenesis, immune response regulation, and chromatin remodeling. Although BLV- and BFV-derived miRNAs target different genes, these targets participate in shared biological processes, suggesting a functional convergence that may influence disease progression and BFV dissemination. These findings offer opportunities for developing diagnostic and therapeutic strategies to control viral persistence and tumor development in cattle.

Introduction: Bovine leukemia virus is a single-stranded RNA virus that targets B cell CD5+ lymphocytes in cattle. Only a tiny percentage of individuals develop malignant lymphoproliferative disorders, while most remain healthy carriers or experience persistent lymphocytosis. The exact mechanisms leading to lymphoma development are complex and not fully understood. RNA-seq analysis of cows’ peripheral blood leukocytes (PBLs) with and without Bovine leukemia virus (BLV) antibodies was conducted to gain a deeper understanding of molecular events beyond BLV infection. Method: Eighteen samples were selected, and their RNA was sequenced. For gene expression analysis and protein–protein network interactions, three groups were selected, including healthy negative samples (CT, n = 7), asymptomatic carriers (AC, n = 5), and persistent lymphocytosis (PL, n = 6), to provide the differentially expressed gene (DEG) and protein–protein interaction network (PPIN) outputs. Results: Our results demonstrated that in comparison to CT, ACs upregulated TLR7 and transcription activation factors. In the CT vs. PL group, MHC class II, transcription activation factors, and anti-inflammatory cytokines increased, while the acute-phase proteins, antiviral receptors, and inflammatory cytokines decreased. Additionally, antiviral receptors, acute-phase proteins, and inflammatory receptors were downregulated in the PL versus the AC groups. Moreover, PPINs analysis suggested that nuclear receptor corepressor 1 (NCOR1), serine/arginine repetitive matrix 2 (SRRM2), LUC7 like 3 pre-mRNA splicing factor (LUC7L3), TWIST neighbor (TWISTNB), U6 small nuclear RNA and mRNA degradation associated (LSM4), eukaryotic translation elongation factor 2 (EEF2), ubiquitin C (UBC), CD74, and heterogeneous nuclear ribonucleoprotein A2/B1 (HNRNP A2B1) are possible hub gene candidates in the PL group. Conclusions: Our results suggest that innate and cellular immune responses are more loose in severe BLV infectious conditions, while the PPINs revealed that new protein interactions are necessary for oncogenesis.

To determine the seroprevalence of infectious agents with reproductive implications in cattle from 3 districts of the high Andean region of Peru over 3,500 m above level sea. 361 blood samples were collected from cows in 3 districts of the Apurimac department using nonprobabilistic stratified sampling for an exploratory study. Antibodies against Brucella spp, Mycobacterium avium subsp paratuberculosis, bovine viral diarrhea virus, bovine leukemia virus, bluetongue virus, bovine herpesvirus 1 (BHV), and Neospora caninum (NC) were detected by ELISA. Analysis of independence, multiple correspondence, and logistic regression were performed for risk factors, with district, age, and phenotypic traits as predictors. The highest seroprevalences were 18.28% BHV and 6.93% NC, with a similar trend at the sector and herd levels. Bovine herpesvirus 1 was predominant in Cotaruse and Oropesa and NC in Oropesa and San Jerónimo. The multiple correspondence analysis explained 42.40% of the structural variability, with greater dispersion observed between seropositives for NC and BHV, without a significant association between seropositivities. The district was a risk factor for NC, with a 95% CI of 0.11 to 0.88 in Cotaruse, although the 95% CI for BHV was 7.33 to 630.75 in Cotaruse and 14.11 to 1,289.94 in Oropesa. BHV and NC are seroprevalent in cows from the sampled high Andean herds, and district location is the strongest risk factor. Environmental conditions and livestock management practices of the region could explain the seroprevalence rates; however, strengthening surveillance against BHV and NC is imperative to prevent risks of acute or subclinical infections.

Development of DNA technologies for genotyping Bovine leukemia virus

Effect of dietary supplementation with Saccharomyces cerevisiae fermentation product on clinical outcomes in dairy cows during challenge with Streptococcus uberis.

Enzootic bovine leukosis (EBL) caused by the bovine leukosis virus (BLV) disturbs the immune response in bovines, leading to severe economic losses, with a possible impact on public health. EBL has no treatment or vaccine available, making the identification of genetic polymorphisms related to BLV resistance in locally adapted breeds like Crioula Lageana cattle valuable perspectives. This study aims to determine the presence of the BoLA-DRB3 alleles associated with susceptibility or resistance to BLV in Crioula Lageana cattle. For that, 208 Crioula Lageana bovines, spanning various ages, categories, and sexes, were subjected to blood sampling for DNA extraction for genetic characterization. The PCR targeted the 440-bp fragment of the env gene of the BLV and 284-bp for the alleles of the BoLA-DRB3 gene. The alleles were identified using Sanger sequencing, and the allele amount and frequency were determined by direct counting. For the determination of resistance or susceptibility, firstly the association between each allele and infection by BLV was determined using the chi-square test (p < 0.05), and then it was followed by an odds ratio analysis. The occurrence of BLV was 38.46% (80/208). The DRB3*12:01 allele was associated with resistance to BLV infection (p = 0.035, O.R. = 0.000. The presence of alleles linked to resistance to disease incidence highlights the potential to enhance genetic approaches in formulating management and control strategies for EBL in diverse cattle populations, with potential implications for livestock production, food safety, and public health.

Bovine leukemia virus (BLV) infects B cells in ruminants and causes lymphoma after an extended latency period. Previous studies have demonstrated T-cell exhaustion through the upregulation of immunoinhibitory molecules, including programmed death-ligand 1 (PD-L1) and T-cell immunoglobulin and mucin domain-3 (TIM-3), in BLV-infected cattle. However, studying T-cell exhaustion across all BLV infection stages remains challenging due to the virus's prolonged latency in cattle. Sheep provide a valuable model, as they develop lymphoma more rapidly than cattle. This study examined PD-L1 and TIM-3 expression kinetics and T-cell function in BLV-infected sheep. During persistent infection, PD-L1 expression was correlated with BLV proviral load. TIM-3 expression increased in CD4+, CD8+, and γδTCR+ T cells. Functional analysis revealed that TIM-3 blockade enhanced T-cell activation markers (CD25 and CD69) in cultured PBMCs from infected sheep and increased CD69+IFN-γ+ and CD69+TNF-α+ populations, particularly among CD4+ T cells. Combined PD-L1 and TIM-3 blockade significantly enhanced cytokine production in both CD4+ and CD8+ T cells, while PD-L1 blockade alone showed limited effects. These findings demonstrate the effect of TIM-3 blockade in restoring immune function during chronic BLV infection, effective both alone and in combination. This study validates sheep as a valuable model for investigating immune checkpoint dynamics and evaluating immunotherapies for BLV infection and other chronic diseases.

Bovine leukemia virus (BLV) is widespread globally and causes economic losses in the cattle industry. BoLA-DRB3 is a polymorphic gene associated with the BLV proviral load (PVL), which correlates with disease progression and transmission risk. However, the distribution of BoLA-DRB3 alleles in semen and their potential impact on the PVL of progeny remain unclear. Here, we investigated whether BLV susceptibility linked to BoLA-DRB3 alleles in semen is inherited by progeny. We analyzed 178 commercial semen samples from Japanese Black sires and identified 20 BoLA-DRB3 alleles and 70 genotypes. The susceptible allele DRB3*016:01 was the most frequent (26.4%), whereas resistant alleles DRB3*011:01 (5.3%) and DRB3*009:02 (0.6%) were rare. Subsequently, we collected blood samples from 200 progeny produced by artificial insemination using 36 of the 178 semen samples. Progeny derived from semen carrying at least one susceptible allele and no resistant alleles had significantly higher PVL in the blood than those derived from semen containing at least one resistant allele. These findings demonstrate that BLV susceptibility is inherited via BoLA-DRB3 alleles in semen and highlight the potential of BoLA-DRB3 alleles as valuable markers in breeding strategies aimed at mitigating BLV infection and transmission.

Coinfections can alter the adaptive immune responses to bovine tuberculosis (bTB) and hinder accurate diagnosis; however, their effect on host immunity to Mycobacterium bovis and disease progression is not well understood. In this study, we assessed the impact of natural coinfection with bovine leukemia virus (BLV) on immune responses to M. bovis. Among 108 cattle examined, those coinfected with BLV showed a significantly higher intragranulomatous mycobacterial burden and more severe pathological lesions compared to animals infected with M. bovis alone. Additionally, coinfected animals demonstrated a granulomatous response characterized by reduced lymphocyte populations, increased neutrophil infiltration, and diminished granuloma encapsulation, suggesting a compromised antimycobacterial immune response. Supporting this hypothesis, BLV-infected cattle exposed to mycobacterial antigens displayed impaired delayed-type hypersensitivity (type IV hypersensitivity) to a purified protein derivative of M. bovis as well as reduced antibody response. These findings indicate that BLV coinfection influences the immunopathogenesis of bTB, exacerbates disease progression in cattle naturally infected with M. bovis, and may reduce the predictive reliability of diagnostic methods used in bTB control programs.

This study critically reviews the literature on the prevalence and genotypic distribution of Bovine Leukemia Virus (BLV) in Asia, specifically targeting enzootic bovine leukosis, a chronic disease affecting cattle’s life and milk production along with reduced fat yield, that causing economic losses due to increased susceptibility to pathogens. European countries are eradicating BLV but Asia has a high prevalence, particularly in Asian cattle. Enzootic bovine leukosis (EBL) has distinct clinical stages: asymptomatic, persistent lymphocytosis, and lymphosarcoma. It typically occurs in adult animals, with 60% being asymptomatic during the aleukemic stage, 30% developing persistent lymphocytosis, and 5% developing lymphoma. Databases like PubMed and Google Scholar were used to search molecular and prevalence studies from 2000-2024, focusing on Asian countries. Prevalence of bovine leukosis (BL) in Asia varies significantly, with high rates in central and eastern regions. BLV is a global disease, has increased in Asia with highest prevalence in central Asia about 40.0–84.0% (Kazakhstan), 35% in Eastern Asia (Japan), and 58.3% in Southeast Asia (Thailand). BLV genotypes G1, G4, G6, G7, G12, G3, G4, G6, G7, and G10 are prevalent in various regions of Asia, with G1 being most prevalent globally. These genotypes might be spread due to animal trading, and animal domestication, affecting various countries. This review provides the current status of enzootic bovine leukosis in Asia, emphasising the need for a closed trading system to control the disease.

ABSTRACTBackground and Aim:Bovine leukemia virus (BLV) is a globally distributed retrovirus that causes enzootic bovine leu-kosis, a chronic infection associated with significant economic losses in cattle. Conventional serological diagnostic tools such as agar gel immunodiffusion and enzyme-linked immunosorbent assay detect anti-BLV antibodies but cannot identify proviral DNA, especially in early infections or in calves with maternal antibodies. This study aimed to develop a sensitive and specific duplex quantitative polymerase chain reaction (qPCR) assay targeting the env gene of BLV with β-actin as an internal control and apply it for molecular surveillance and genotyping of BLV in cattle from six regions of Kazakhstan.Materials and Methods:A total of 1,680 bovine DNA samples from cattle aged over 3 years were collected from six administrative regions of Kazakhstan. A duplex qPCR assay was developed using primers targeting a conserved region of the BLV env gene and bovine β-actin. Sensitivity was assessed using plasmid and genomic DNA dilutions, and specificity was tested against existing WOAH-recommended and commercial polymerase chain reaction (PCR) protocols. Positive samples with cycle threshold <28 were subjected to nested PCR and Sanger sequencing for genotyping. Phylogenetic analysis was conducted using the maximum likelihood method.Results:The developed qPCR assay demonstrated a sensitivity of 20 plasmid copies for the env gene and 6 genomic equivalents for β-actin per reaction, with high specificity comparable to international standards. The overall BLV infection rate was 38.9%, ranging from 13% in Pavlodar to 60.5% in East Kazakhstan. Among 149 sequenced positive samples, four genotypes (G1, G4, G7, and G8) were identified. Genotype G4 was predominant, comprising 79.2% of sequences and present in all six regions.Conclusion:The duplex qPCR assay is a robust, sensitive, and cost-effective diagnostic tool for detecting BLV provirus, including in animals with maternal antibodies or early-stage infections. The regional genotypic distribution underscores the need for tailored control strategies. This molecular surveillance provides essential baseline data for national BLV eradication programs and contributes to global BLV epidemiological mapping.

Bovine leukemia virus (BLV) is a globally prevalent pathogen that can cause enzootic bovine leukosis (EBL), which reduces dairy cows' immunity, interferes with mammary antimicrobial defense capabilities, and exacerbates clinical mastitis. However, the specific mechanisms by which these effects occur remain incompletely understood. Ferroptosis, an iron-dependent non-apoptotic cell death mechanism, exhibits dual roles in viral infections. In this study, wild-type BLV and a miRNA-deficient mutant strain (BLV-ΔmiRNA) were used to infect bovine mammary epithelial cells in vitro, combined with non-targeted metabolomics to investigate BLV-regulated ferroptosis evidence. The results shown that BLV significantly elevated levels of unsaturated fatty acid, interferes with vitamin B6 metabolism. Suggest that BLV promote ferroptosis in mammary epithelial cells through unsaturated fatty acid biosynthesis and vitamin B6 metabolism pathways, potentially involving BLV-encoded miRNAs. This research provides a theoretical foundation for identifying novel BLV pathogenic targets and prevention strategies.