Enzootic Bovine Leukemia Research Articles

Chimeric provirus of bovine leukemia virus/SMAD family member 3 in cattle with enzootic bovine leukosis.

Bovine leukemia virus (BLV) is a member of the family Retroviridae that causes enzootic bovine leukemia (EBL). However, the association between BLV infection and EBL development remains unclear. In this study, we identified a BLV/SMAD3 chimeric provirus within CC2D2A intron 30 in monoclonal expanded malignant cells from a cow with EBL. The chimeric provirus harbored a spliced SMAD3 sequence composed of exons 3-9, encoding the short isoform protein, and the BLV-SMAD3 chimeric transcript was detectable in cattle with EBL. This is the first report of a BLV chimeric provirus that might be involved in EBL tumorigenesis.

Structural characteristics of the bovine leukemia virus genome: A mini review

Enzootic bovine leukemia is an infectious disease with a chronic course caused by an RNA‑containing virus of the genus Deltaretrovirus. Despite the implementation of various programs for the elimination of leukemia, the disease is still widespread on the planet and continues to cause significant economic damage. A large proportion of BLV‑infected cattle remain to be asymptomatic carriers of the virus, which complicates diagnosis and contributes to the spread of the disease in the herd. The structure of the BLV genome is generally typical of retroviruses. It consists of genes encoding structural proteins, viral enzymes and regulatory elements flanked on both sides by identical long terminal repeats. The enzyme and structural protein coding genes (gag, pro, pol, and env) play a crucial role in the life cycle of the virus, influencing its infectivity and virion production. The tax and rex regulatory genes regulate viral transcription, export of transcripts from the nucleus to the cytoplasm, and disease progression. The increase in the number of copies of proviral DNA occurs mainly not due to the functioning of the virus reverse transcriptase, but because of clonal reproduction of the affected subpopulations of B‑cells, mainly CD5+ IgM+. This feature provides increased genetic stability of the BLV virus. These properties of the viral genome allow the development of a variety of PCR test systems. The widespread implementation of such systems enables the detection of carriers of the disease at early stages, which should contribute to the effective implementation of national programs to eradicate bovine leukemia.

Effect of BLV Infection on the Immune Function of Polymorphonuclear Neutrophil in Dairy Cows.

Enzootic bovine leukemia is a late-onset, neoplastic infection caused by the bovine leukemia virus (BLV). BLV infection hinders the function of the immune system and induces other diseases, which negatively affects the performance and health of the infected cows. As the first line of defense against invading foreign pathogenic microorganisms, polymorphonuclear neutrophil (PMN) plays a vital role in the immune system of dairy cows. However, research on the effect of BLV infection on the immune function of PMN in dairy cows is scarce. Therefore, this experiment aimed to elucidate the effects and effect mechanisms of BLV infection on the immune function of PMN in dairy cows with different BLV provirus loads by detecting the chemotaxis, migration, adhesion, phagocytosis, respiratory burst function, and the formation of NETs. The experimental results showed that BLV infection had no significant effect on the phagocytosis of PMN but inhibited their migration and respiratory burst function, and the effects were closely related to the BLV provirus load. Under high BLV provirus load, PMN produced large amounts of NETs, chemokine CXCL7, adhesion molecule CD18, and pro-inflammatory factors IL-8 and TNF-α, triggering inflammatory responses, and tissue damage. The results of this study will help reveal the reason why BLV infection causes the high incidence of mammary gland inflammation in dairy cows.

Seropositivity for Bovine Viral Diarrhea and Enzootic Bovine Leukemia viruses in Blanco Orejinegro cattle in Colombia and infection associated-factors

Serological controls for diseases of viral origin in animal production systems and the identification of factors associated with infections are decisive elements to establish prevention and control measures. The aim of this study was to establish the serological status for Bovine Viral Diarrhea (BVD) and Enzootic Bovine Leukemia (EBL) viruses in Blanco Orejinegro (BON) cattle from Colombia, and to identify the factors associated with seropositivity. A cross-sectional study was conducted with a total of 498 animals of all age groups and physiological states of the BON breed were selected, belonging to 14 herds located in 6 states of Colombia, in which a survey with 27 questions was conducted. By means of the chi-square test, possible factors associated with seropositivity against the 2 viruses were identified. A sample of 4 ml of blood was taken from each animal to extract plasma and make indirect Elisa tests to detect antibodies against both pathogens. General seropositivity of 27,1% was obtained for EBL, finding as factors associated with seropositivity the inadequate disposition of placental tissues after delivery of the cows and the non-performance of serological tests on new animals entering the herd. For BVD, seropositivity obtained was 50,6%, and the factors associated with seropositivity identified were having had a history of the disease in the herd, and using semen from bulls that are not known to be free for the infection. We suggest establishing control measures considering the factors associated with each viral infection to limit their expansion in the BON cattle production systems of Colombia.

Autotransporter-based surface expression and complementation of split TreA fragments utilized for the detection of antibodies against bovine leukemia virus

Bovine Leukemia Virus (BLV) is an oncogenic virus which is the etiological agent of a neoplastic disease in infected cattle called enzootic bovine leukemia (EBL). The most common and sensitive diagnostic methods for EBL like enzyme-linked immunosorbent assay (ELISA) is time-consuming and requires manual handling which makes it unsuitable as an on-farm diagnostic test. Hence, there is a need for an alternative test with rapid detection and reduced manual labour. We have previously reported the use of E. coli periplasmic trehalase (TreA) in a split enzyme sensor diagnostic technology to detect immunoglobulins and antigen-specific antibodies. In the current study, a more sensitive detection was attempted by bacterial surface display of split TreA fragment by fusion with the autotransporter AIDA-I. The split TreA fragments fused to antigens require antigen-specific antibodies for complementation and to trigger trehalase activity. This surface complementation strategy was used to detect anti-BLV antibodies in clinical serum by incorporating the antigenic BLV capsid protein in the fusion proteins. To validate this assay, a panel of serum samples obtained from BLV positive and negative cattle were tested in comparison with ELISA results. Evaluation of this panel resulted in positive detection of all true positive samples. We further demonstrated that this assay can be enhanced by pre-adsorption of clinical serum samples using E. coli cells to increase the specificity and help reduce nonspecific binding. In conclusion, the p24 antigen specific BLV assay is a potential tool for simple and rapid diagnosis of BLV infection, which is compatible with both lab-based and a more user friendly on-farm format.

Prediction of B cell and T-helper cell epitopes candidates of bovine leukaemia virus (BLV) by in silico approach.

The bovine leukaemia virus (BLV) is a retrovirus responsible for enzootic bovine leukaemia (EBL) disease, the most common cattle disease leading to high annual economic losses to the cattle breeding industry. Virus monitoring among the sheep and cattle herds is usually done by vaccination. Inactivated virus vaccines can partially protect the livestock from viral challenge. However, vaccinated animals are likely to be infected. So, there is an essential need for producing vaccine by other methods. Gp60 SU, encoded by Env gene, is the surface glycoprotein of BLV detected to be the major target for the host immunity against the virus. Different stages were performed to predict the potential B and T‐helper cell epitopes. The general framework of the method includes retrieving the amino acid sequence of gp60 SU, conducting the sequence alignment, getting the entropy plot, retrieving the previously found epitopes, predicting the hydropathy parameters, modelling the tertiary structure of the glycoprotein, minimizing the structure energy, validating the model by Ramachandran plot, predicting the linear and discontinuous epitopes by various servers and eventually choosing the consensus immunogenic regions. Ramachandran plot scrutiny has demonstrated that the modelled prediction is accurate and suitable. By surveying overlaps of various results, 4 and 2 immunogenic regions were selected as linear and conformational epitopes respectively. Amino acids 35–53, 67–97, 288–302 and 410–421 and those of numbers 37–58 and 72–100 were the regions selected as linear and conformational epitopes respectively. The tertiary structure of the final epitope was modelled as well. A comparison of the predicted epitopes structure with that of gp60 SU envelope, illustrated that the tertiary structure of these epitopes does not change after being separated from the primary complete one. The present achievements will lead to a better interpretation of the antigen–antibody interactions against gp60 in the designing process of safe and efficient vaccines.

Epidemiological study of neosporosis in Uruguayan dairy herds

Neosporosis is one of the leading causes of abortion in cattle worldwide, posing a great economic burden on cattle producers. The aim of this study was to determine the national seroprevalence and putative risk factors of Neospora caninum (N. caninum) in dairy cattle in Uruguay. A cross-sectional study was carried out. Herds were stratified by size (1-50, 51–250, and >250 cattle) and up to 60 dairy cows per herd were randomly selected. Four thousand two hundred twenty-three serum samples from 102 dairy herds were analyzed by indirect ELISA test, under the manufacturer's recommendations. In addition, the herdsman was surveyed and a population study was carried out. The in degree data, geographical coordinates, and seroprevalence of bovine viral diarrhea, enzootic bovine leukemia and infectious bovine rhinotracheitis were available for each herd. A sampling design was used to estimate population seroprevalence of N. caninum. In order to determine the factors associated with the disease, herds with an intra-herd seroprevalence over 20% were considered as case herds. Seroprevalence of N. caninum was 22.3% (95% CI: 18.7-25.9 %) and 96.0% (95% CI: 92.1-99.8%) at the animal and herd level, respectively. The number of dogs on the dairy farms were associated with infection levels (OR: 1.43, 95% CI: 1.02 to 2.03). It was concluded that N. caninum is endemic in the country, and is spreading over dairy herds. Although this study showed evidence that the number of dogs were associated with high levels of infection, more studies should be conducted, to better understand the epidemiology of the disease and thus develop efficient control measures.

Risk assessment for interspecies transmission of enzootic bovine leukemia

Conducted three series of infecting the rabbits with bovine leukemia virus (BLV) using milk and blood from cows having enzootic leukemia with different doses of infecting material and different mode of administration showed a high degree of repeatability of the experiment. The obtained results testify to the ability of BLV to successfully overcome the interspecific barrier when ingested by an alimentary pathway with milk, as well as by the direct injection of infected lymphocytes into the bloodstream.

Detección molecular y serológica del virus de la leucosis bovina en una población de vacas Holstein, de Colombia

La leucosis bovina enzoótica (LBE) es una enfermedad maligna, sistémica, de alta morbilidad (70 %) y baja mortalidad, ocasionada por la infección con el virus de la leucosis bovina (BLV). La LBE afecta principalmente los bovinos de leche, disminuyendo la producción de leche de 2.5 a 5 % respecto al hato; además, causa inmunosupresión, permitiendo que otros patógenos afecten la producción y reproducción de los animales. El objetivo fue determinar la presencia o ausencia del BLV a través de dos metodologías de diagnóstico: una técnica serológica (ELISA) y una técnica molecular (PCR). Se tomaron 1,000 muestras de sangre de vacas Holstein distribuidas en 10 municipios lecheros del Departamento de Antioquia. Se realizó una PCR para obtener un producto de PCR de 444 pb correspondiente a una región altamente conservada del gen env viral, que codifica para la proteína de envoltura gp51. Se realizó un ELISA indirecta contra la proteína gp51 para estos mismos animales. La PCR detectó un número menor de muestras positivas (474) que la prueba ELISA (546). La sensibilidad de la PCR fue de 74.91 % y su especificidad fue de 85.68 % respecto al ELISA. El grado de concordancia entre pruebas fue moderado (kappa=0.59). El municipio con la mayor prevalencia molecular fue Rionegro (73.91 %), mientras que la mayor seroprevalencia se registró en el municipio de El Retiro (85.19 %). El BLV ha aumentado su presencia en la región; la detección de este patógeno no solo permitirá determinar la prevalencia, sino también usar los datos obtenidos en programas de prevención y control de la enfermedad.

SEROPREVALENCIA DE LEUCOSIS ENZOÓTICA BOVINA EN ANIMALES ENTRE 6 A 24 MESES EN LAS PROVINCIAS DE MANABÍ, PICHINCHA Y CHIMBORAZO - ECUADOR

La Leucosis Enzoótica Bovina (LEB o LVB) es una enfermedad vírica, manifestada por la presencia de neoplasiasy también presentándose de forma asintomática en bovinos de cualquier edad. Su trascendencia socioeconómicaradica en las pérdidas por disminución de la productividad lechera, pérdidas reproductivas y decomisos en camales,impidiendo también la exportación de ganado o derivados del mismo. El objetivo de esta investigación fue determinarla seroprevalencia de LEB en animales menores de dos años en las provincias de Pichincha, Manabí y Chimborazo,las cuales reportan gran producción lechera en Ecuador. Se analizaron 3 307 muestras de suero sanguíneo bovinomediante la técnica serológica ELISA indirecto, de las cuales 480 fueron de Pichincha, 2 348 de Manabí y 479 deChimborazo. Pichincha presentó una seroprevalencia de 8.13%, con el mayor porcentaje de animales enfermos enla principal cuenca lechera del país, el cantón Mejía. En Manabí se observó 0.89% de seroprevalencia de LEB y enChimborazo 3.13%. Utilizando chi cuadrado para determinar la relación entre las variables evaluadas y la apariciónde LEB, se reveló que no existe asociación, mostrando un resultado de 105.14, 7.48, 140.91 y 38.87 frente a valores dep de 11.34 (clima), 9.21 (altitud), 18.48 (edad) y 9.21 (propósito del ganado). Sin embargo, se observó mayor tendenciaa enfermar en clima templado y mayor altitud, lo que pudo explicarse por la similitud en las prácticas de manejoy la explotación tipo intensivo. Los datos obtenidos significan una línea base de estudio de la cual se puede partirpara elaborar un plan de control sanitario de LEB desde edades tempranas del ganado bovino y emprender en otrasinvestigaciones.

Seroprevalencia de infección por el virus de leucosis bovina durante 2015 en rodeos de cría de la Zona Deprimida del Río Salado, provincia de Buenos Aires, Argentina

La leucosis enzoótica bovina (LEB) es una enfermedad crónica, linfoproliferativa y altamente contagiosa producida por el virus de la leucosis bovina (VLB). La sangre es una fuente importante de infección, principalmente en la práctica veterinaria, considerando que solo 5 microlitros son suficientes para infectar a un bovino en forma experimental. La Zona Deprimida del Río Salado (ZDRS) está formada por poco más de 6 millones de hectáreas con una cantidad de terneros que representa el 16,05 % de las existencias nacionales y el 34,03 % de las provinciales, convirtiéndose, de ese modo,en la principal zona criadora de terneros de Argentina. Los últimos estudios sobre seroprevalencia de infección por el VLB en rodeos de cría en la provincia de Buenos Aires se realizaron hace poco más de 20 años, obteniéndose valores inferiores al 2 %. En este trabajo se analizaron un total de 1957 bovinos de cría provenientes de 90 establecimientos, representando poco más del 85 % de la superficie de la ZDRS, para determinar la presencia de anticuerpos contra el VLB mediante inmunodifusión en gel de agar, prueba utilizada en estudios epidemiológicos y en planes de erradicación de la enfermedad. La prevalencia en los establecimientos fue del 6,6 %, mientras que se obtuvo una seroprevalencia individual de 0,36 %. Debido a que la ZDRS es la de mayor productividad de terneros de cría en Argentina, es de sumo interés determinar la prevalencia de infección en esta región para establecer zonas libres de VLB.

Cytokine profiles of dendritic cells (DCs) during infection with bovine leukaemia virus (BLV).

BLV is an agent of enzootic bovine leukaemia (EBL), an infectious disease affecting cattle worldwide. BLV infection has been associated with immune system disorders and discrepancies in the cytokine network. The significance of dendritic cells in the pathogenesis of BLV infection is largely unknown, but considering their fundamental role in immune response it may be crucial. DCs precursors were isolated with the use of immunomagnetic beads from BLV-infected and BLV-free cows. From these precursors cultures of monocyte derived dendritic cells (MoDCs) were generated with the use of a cytokine cocktail (IL-4 and GM-CSF). Additionally, parallel DCs from BLV-negative animals were infected in vitro. The level of cytokines: IL-6, IL-10, IL-12(p40), IL-12(p70) was determined in DC cultures: infected in vitro, originating from naturally infected cattle and BLV-free cattle. The investigation showed significant changes in almost all analyzed populations of BLV-infected DCs. Cytokine profiles of blood MoDCs indicated activation of these groups during infection. In the case of spleen MoDCs and lymph node MoDCs a decrease in production of IL-12(p40) and IL-12(p70) in favour of IL-6 and IL-10 was noted, suggesting promotion of BLV infection development.

Intrauterine infection with bovine leukemia virus in pregnant dam with high viral load.

Enzootic bovine leukemia is caused by the bovine leukemia virus (BLV). BLV is transmitted vertically or horizontally through the transfer of infected cells via direct contact, through milk, insect bites and contaminated iatrogenic procedures. However, we lacked direct evidence of intrauterine infection. The purpose of this study was to confirm intrauterine BLV infection in two pregnant dams with high viral load by cesarean delivery. BLV was detected in cord and placental blood, and the BLV in the newborns showed 100% nucleotide identity with the BLV-env sequence from the dams. Notably, a newborn was seropositive for BLV but had no colostral antibodies. In this study, we presented a direct evidence of intrauterine BLV transmission in pregnant dam with a high proviral load. These results could aid the development of BLV control measures targeting viral load.

DETECCIÓN SEROLÓGICA DEL BLV EN MUESTRAS DE LECHE EN UNA POBLACIÓN DE VACAS HOLSTEIN, ANTIOQUIA

The Bovine Leukosis Virus (BLV) is the etiological agent of the Enzootic Bovine Leukemia (EBL), this disease is infectious, chronic and specifically cattle, presenting a low percentage of patients with clinical manifestations. Between 30-70% of infected animals can develop persistent lymphocytosis (LP) and between 0,1-10% of cattle over three years of infection suffers some form of lymphosarcoma (LS). The aim of this work was serologically detection of BLV in milk samples from Holstein cows in three dairy herds in the department of Antioquia. Were taken 133 milk samples from Holstein cows three dairy herds located in the municipality of Medellin and Belmira, was conducted an indirect ELISA against gp51 envelope protein of the virus. The ELISA test showed a seroprevalence of 79,69% (106/133) for all samples tested. The herd was the largest herd seroprevalence 1 (82,86%), followed by the herd 2 (80%) and finally the herd 3 (77,08%). The presence of the BLV has increased in recent years in Antioquia, so fast and efficient diagnosis through reliable methodologies allow control over the spread of the disease in dairy herds.

Detección molecular del virus de la leucosis bovina: un estudio por conglomerados en Colombia

La leucosis bovina enzoótica (LBE) es ocasionada por un virus de la familia Retroviridae, el virus de la leucosis bovina (VLB), que afecta bovinos de cualquier edad, sexo y raza y genera importantes pérdidas económicas. En Colombia, los pocos estudios moleculares se concentran en ganado de leche; por ello, el presente trabajo se dirigió a detectar el VLB mediante una prueba molecular de PCR en animales destinados a diferentes tipos de explotación ganadera y de diferentes regiones del país, con el propósito de evaluar la relación entre la presencia del VLB en los animales, la ubicación geográfica y el tipo de explotación bovina. De un total de 230 animales, organizados por conglomerados según la región de origen, el 22.6 % se detectó con el VLB; de estos la región Centro presentó el mayor número de animales infectados (50.7 %). En cuanto al tipo de producción, el ganado de leche fue el más susceptible a ser infectado por el VLB (50.7 %). Los resultados indican que existe una significativa relación entre la presencia molecular del virus, la ubicación geográfica de los animales y el tipo de explotación bovina, datos importantes para la planeación de programas de prevención y control de la LBE por los organismos gubernamentales de salud animal.

Genome-wide association study for host response to bovine leukemia virus in Holstein cows

The mechanisms of leukemogenesis induced by bovine leukemia virus (BLV) and the processes underlying the phenomenon of differential host response to BLV infection still remain poorly understood. The aim of the study was to screen the entire cattle genome to identify markers and candidate genes that might be involved in host response to bovine leukemia virus infection. A genome-wide association study was performed using Holstein cows naturally infected by BLV. A data set included 43 cows (BLV positive) and 30 cows (BLV negative) genotyped for 54,609 SNP markers (Illumina Bovine SNP50 BeadChip). The BLV status of cows was determined by serum ELISA, nested-PCR and hematological counts. Linear Regression Analysis with a False Discovery Rate and kinship matrix (computed on the autosomal SNPs) was calculated to find out which SNP markers significantly differentiate BLV-positive and BLV-negative cows. Nine markers reached genome-wide significance. The most significant SNPs were located on chromosomes 23 (rs41583098), 3 (rs109405425, rs110785500) and 8 (rs43564499) in close vicinity of a patatin-like phospholipase domain containing 1 (PNPLA1); adaptor-related protein complex 4, beta 1 subunit (AP4B1); tripartite motif-containing 45 (TRIM45) and cell division cycle associated 2 (CDCA2) genes, respectively. Furthermore, a list of 41 candidate genes was composed based on their proximity to significant markers (within a distance of ca. 1 Mb) and functional involvement in processes potentially underlying BLV-induced pathogenesis. In conclusion, it was demonstrated that host response to BLV infection involves nine sub-regions of the cattle genome (represented by 9 SNP markers), containing many genes which, based on the literature, could be involved to enzootic bovine leukemia progression. New group of promising candidate genes associated with the host response to BLV infection were identified and could therefore be a target for future studies. The functions of candidate genes surrounding significant SNP markers imply that there is no single regulatory process that is solely targeted by BLV infection, but rather the network of interrelated pathways is deregulated, leading to the disruption of the control of B-cell proliferation and programmed cell death.

Bovine Leukemia: Zoonosis Associated with Breast Cancer in Humans?

Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukemia. It is proposed that BLV is restricted to bovines, but there are some reports of its presence in humans and its possible relationship with breast cancer. Considering that any relation or association between this virus and breast cancer could be relevant to human public health and to cattle producers worldwide, it is crucial that several research groups keep investigating in the topic with the aim of confirming the role that this virus should have in breast cancer development. Due to the lack of a vaccine, prevention and control strategies should be implemented by governments where livestock is rising.

Distribution and characteristics of bovine leukemia virus integration sites in the host genome at three different clinical stages of infection.

Bovine leukemia virus (BLV) is an oncogenic retrovirus closely related to human T-cell lymphotropic virus. BLV-infected cattle are categorized as asymptomatic carriers or as having persistent lymphocytosis or enzootic bovine leukemia, depending on the clinical stage. We investigated the BLV integration site distribution at three BLV clinical stages and examined genome sequence features around the integration sites. In all, 264 BLV integration sites, at various locations on each chromosome, were identified in 28 cattle by inverse PCR and BLAST searches. Approximately one-third of BLV proviruses were independently integrated within transcriptional units, and approximately 10 % were integrated near transcription start sites. Moreover, less than 7 % of BLV integration sites were located near CpG islands. BLV did not preferentially integrate into transcriptionally active regions during any of the clinical stages. At the nucleotide level, regions around BLV integration points were significantly A/T rich with weak sequence consensus. BLV preferentially integrated within long interspersed nuclear repeat elements. Although BLV integration sites may not be associated with disease progression, integration is selective at the nucleotide level.

Analysis of the pX region of bovine leukemia virus in different clinical stages of Enzootic Bovine Leukemia in Argentine Holstein cattle

Bovine leukemia virus (BLV) infection in cattle causes Enzootic Bovine Leukemia (EBL). About 30% of infected cattle develop persistent lymphocytosis (PL), a 0.1–5% develops tumors, and a 70% remains asymptomatic in an aleukemic stage (AL). Regulatory genes of BLV (Tax, Rex, R3 and G4) are located in a region known as pXBLV. The variability of those genes had been postulated with the progression of the disease. The aim of this work was to compare the wild-type proviral pXBLV region at different stages of BLV natural infected cattle from Argentine Holstein. Pairs of primers were designed to amplify the proviral pX region of 12 cattle by PCR, and products were then sequenced, aligned and compared both with each other and with the reference sequence. Results show a divergence percentage from 0 to 6.1 for the Tax gene, from 0 to 9.4% for the Rex gene, from 0 to 12.1% for the R3 gene and finally from 0 to 6.5% for the G4 gene. Results obtained with hierarchical clustering showed two clusters well differentiated, where the members of each cluster are cattle that had tumor, PL and AL, not allowing differentiate those two cluster by clinical stage.

A Serological Study on Bovine Leukemia Virus Infection in Ten Provinces of Iran between 2010 and 2012

Background and Aims: Bovine leukaemia virus (BLV) is an oncogenic member of the genus Deltaretrovirus of the family Retroviridae. BLV is the causative agent of enzootic bovine leukaemia and infects cattle worldwide, imposing economic impact on the dairy cattle industry. The purpose of this study was to estimate the seroprevalence of BLV in cattle in some provinces of Iran. Materials and Methods: A total of 280 cows over 2 years old from 10 provinces of Iran in different regions and environments from industrial and less industrial herds were used in the study. Blood samples from all cows were taken both with and without EDTA. Serum separation for the ELISA test and leukocyte count, were performed upon receipt without delay. Cattle without fever that had lymphocyte numbers of more than 9,000/μl were suspected to have persistent lymphocytosis (PL). Sera samples were examined for antibodies against BLV by blocking ELISA. Results: The seroprevalence of BLV among animals was 32.8% and among provinces was 80%. Seropositive cattle had higher total leukocyte and lymphocyte count and lower neutrophil count than seronegative cattle (P<0.001). Among BLV seropositive animals, the rate of PL was 36.9%. None of the seronegative animals showed lymphocytosis. Conclusion: Comparing the data with previous studies on seroprevalence of BLV in different localities in Iran, the prevalence of the infection has been raised. These results suggest that promoting control programs in Iran are very important. Furthermore, it will be essential to conduct nationwide surveillance program and determine the major risk factors.