The effectiveness of colostral antibodies for preventing bovine leukemia virus (BLV) infection in vitro

The Global Epidemiology of Bovine Leukemia Virus: Current Trends and Future Implications

Bovine leukemia virus (BLV) is a retrovirus that causes enzootic bovine leucosis (EBL), which is the most significant neoplastic disease in cattle. Although EBL has been successfully eradicated in most European countries, infections continue to rise in Argentina, Brazil, Canada, Japan, and the United States. BLV imposes a substantial economic burden on the cattle industry, particularly in dairy farming, as it leads to a decline in animal production performance and increases the risk of disease. Moreover, trade restrictions on diseased animals and products between countries and regions further exacerbate the problem. Recent studies have also identified fragments of BLV nucleic acid in human breast cancer tissues, raising concerns for public health. Due to the absence of an effective vaccine, controlling the disease is challenging. Therefore, it is crucial to accurately detect and diagnose BLV at an early stage to control its spread and minimize economic losses. This review provides a comprehensive examination of BLV, encompassing its genomic structure, epidemiology, modes of transmission, clinical symptoms, detection methods, hazards, and control strategies. The aim is to provide strategic information for future BLV research.

Anti-BLV antibodies in whey correlate with bovine leukemia virus disease progression and BoLA-DRB3 polymorphism

Introduction

Bovine leukemia virus (BLV) belongs to the family Retroviridae and is a causative agent for enzootic bovine leucosis, the most common neoplastic disease affecting cattle worldwide. BLV proviral load (PVL) is associated with disease progression and transmission risk but requires blood collection and quantitative PCR testing. Anti-BLV antibodies in whey have been used as a diagnostic tool for BLV infection; however, quantitative utilization has not been fully investigated. Furthermore, bovine leukocyte antigen (BoLA)-DRB3 is a polymorphic gene associated with BLV infectivity and PVL, but its effect on anti-BLV antibody levels in whey from BLV infected dams is unknown. Therefore, we aimed to investigate whether it is possible to correctly predict PVL in the blood and milk based on the amount of anti-BLV antibodies in milk, and whether the BoLA-DRB3 alleles associate with the amount of anti-BLV antibodies in milk.

Methods

We examined whey from 442 dams from 11 different dairy farms located in 6 prefectures in Japan, including susceptible dams carrying at least one BoLA-DRB3^* 012:01 or ^* 015:01 allele related with high PVL, resistant dams carrying at least one BoLA-DRB3 ^* 002:01, ^* 009:02, or ^* 014:01:01 allele related with low PVL, and neutral dams carrying other alleles.

Results

First, our results provided compelling evidence that anti-BLV antibody levels in whey were positively correlated with the anti-BLV antibody levels in serum and with BLV PVL in blood and milk, indicating the possibility of estimating BLV PVL in blood and milk by measuring anti-BLV antibody levels in whey. Thus, our results showed that antibody titers in milk might be effective for estimating BLV transmission risk and disease progression in the field. Second, we demonstrated that anti-BLV antibody levels in whey from BLV resistant dams were significantly lower than those from susceptible and neutral dams.

Discussion

This is the first report suggesting that the BoLA-DRB3 polymorphism affects anti-BLV antibody levels in whey from BLV-infected dams. Taken together, our results suggested that anti-BLV antibody levels in whey, measured by enzyme-linked immunosorbent assay, may be a useful marker to diagnose the risk of BLV infection and estimate PVL in blood and milk.

BoLA-DRB3 Polymorphism Controls Proviral Load and Infectivity of Bovine Leukemia Virus (BLV) in Milk

Bovine leukemia virus (BLV), which causes enzootic bovine leukosis, is transmitted to calves through the milk of BLV-infected dams. Bovine leukocyte antigen (BoLA)-DRB3 is a polymorphic gene associated with BLV infectivity and proviral load (PVL). However, the effect of BoLA-DRB3 polymorphism on the infectivity and PVL of milk from BLV-infected dams remains unknown. This study examined milk from 259 BLV-infected dams, including susceptible dams carrying at least one BoLA-DRB3*012:01 or *015:01 allele with high PVL, resistant dams carrying at least one BoLA-DRB3*002:01, *009:02, or *014:01:01 allele with low PVL, and neutral dams carrying other alleles. The detection rate of BLV provirus and PVL were significantly higher in milk from susceptible dams than in that from resistant dams. This result was confirmed in a three-year follow-up study in which milk from susceptible dams showed a higher BLV provirus detection rate over a longer period than that from resistant dams. The visualization of infectivity of milk cells using a luminescence syncytium induction assay showed that the infectious risk of milk from BLV-infected dams was markedly high for susceptible dams compared to resistant ones. This is the first report confirming that BoLA-DRB3 polymorphism affects the PVL and infectivity of milk from BLV-infected dams.

Insights into the Research Trends on Bovine Colostrum: Beneficial Health Perspectives with Special Reference to Manufacturing of Functional Foods and Feed Supplements

Bovine colostrum (BC) is the initial mammary secretion after parturition, which is nature's bountiful source consisting of nutritional and bioactive components present in a highly concentrated low-volume format. All mammalian newborns require colostrum to enhance physiological processes such as lifelong immunity, gastrointestinal development, and resistance to microbial infections. The genetic, environmental, and processing methods can all have an impact on the biochemical contents of BC and its supplements. BC and its derivatives have been intensively researched for their potential use in functional foods, medicines, and animal feed. Evidence from clinical studies suggests that BC products are well-tolerated, nontoxic, and safe for human ingestion. Functional foods, feed, and pharmaceutical formulations based on bovine colostrum are playing noteworthy roles in the development of innovative products for promoting health and the prevention of chronic illnesses. This systematic review sheds light on recent research on (a) the effects of processing techniques on BC components, (b) emerging techniques used in the isolation and identification of novel components, (c) BC-based functional foods for human consumption and animal feed supplements, and (d) the role of BC in current drug delivery, as well as future recommendations.

Mutations in the tumor suppressor gene p53 in cattle are associated with enzootic bovine leukosis

Enzootic bovine leukosis (EBL) is a B-cell lymphoma caused by the bovine leukemia virus (BLV). Although an association between EBL and mutations in the bovine tumor suppressor gene TP53 (bTP53) has been suggested, the substantive incidence rate of bTP53 mutations in EBL cattle is still unclear. In this study, we investigated the complete sequence (exons 2-11) of bTP53 in tissue and peripheral blood leukocyte (PBL) samples obtained from 154 EBL cattle and 117 cattle without EBL (non-EBL cattle) to elucidate the correlation between bTP53 mutations and EBL. The detection frequencies of non-synonymous (NS) and deletion mutations in bTP53 in EBL cattle were significantly higher than those in non-EBL cattle in both tissue and PBL samples (p < 0.05). Among these mutations in EBL cattle, 73.7 % (42/54) were homologous to those of human TP53 (hTP53), which were previously detected in various tumors. It has been reported that 95.2 % (40/42) of these hTP53 mutations induced complete or partial loss of the transactivating function of its encoding protein, P53. Moreover, the BLV proviral load in tissue samples was significantly higher in cattle harboring bTP53 NS and deletion mutations than in cattle without these mutations in both EBL and BLV-infected non-EBL cattle (p < 0.05). Although the activity of the mutant variants of bP53 must be further investigated, our findings revealed that bTP53 mutations are involved in tumorigenesis in BLV-infected cells and EBL-associated carcinogenesis.

Avoidance of Natural Suckling from Dams with Bovine Leukemia Virus Is a Low Priority Countermeasure against Postnatal Transmission

Although natural suckling from dams with bovine leukemia virus (BLV) has not been recommended in Japan, the frequency of BLV transmission through natural suckling under natural conditions is still unclear. The purpose of this study was to elucidate the risk of BLV transmission through natural suckling. Dams with BLV were classified into three groups (high, middle, low) based on the proviral loads (PVLs). PCR positivity of their colostrum and the correlations between the ratios of calves with BLV and types of feeding milk were analyzed. In dams with low PVLs, no colostrum or calves were confirmed to have BLV. In dams with middle and high PVLs, 17 out of 25 (68.0%) colostrum were PCR positive, and 10 out of 23 (43.4%) and 13 out of 29 (44.8%) calves with natural suckling and artificial rearing were infected with BLV, respectively. No difference was confirmed between the infection rates of natural-suckled and artificially reared calves. Thus, we concluded that the avoidance of natural suckling from dams with BLV and the introduction of artificial rearing were low priority countermeasures against BLV transmission.

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.

Diagnostic Measures of Disease Progression in Cattle Following Natural Infection with Bovine Leukemia Virus

This study describes the longitudinal changes in bovine leukemia virus (BLV) ELISA antibodies, proviral load (PVL), and blood lymphocyte counts (LC) observed over a 2.5-year period in naturally infected cattle. The dataset utilized was from a BLV intervention field trial on three Midwestern dairy herds. Our analysis showed ELISA false negatives were more likely to occur in cattle with low PVL and normal LC. On average, negligible changes in LC were observed during six-month intervals. Periods of lymphocytosis, defined as >10,000 lymphocytes per uL of blood, were observed in 31.5% (68/216) of BLV test-positive cattle. In BLV test-positive cows, an average increase of 2900 to 3100 proviral copies per 100,000 cells was observed during each subsequent six-month sampling interval. The difference between the minimum and maximum PVL observed for an ELISA-positive cow with 3 or more observations ranged from 0 to 115,600 copies per 100,000 cells (median: 12,900; mean: 19,200). Therefore, following the identification of ELISA-positive cattle and the assessment of PVL and LC, subsequent semiannual tests to assess disease progression may not be needed. Further work is needed to determine how available diagnostic tests can be optimized to design cost-effective testing schemes for BLV control programs.

Influence of the kappa casein genotype on the technological properties of cow milk of Simmental and Alatau breeds

The main objective of dairy farming is to obtain highly productive animals that produce milk with high protein content and have good technological properties. Currently, with the development of molecular genetics and molecular biology, it is possible to identify genes directly or indirectly associated with the milk production of animals. The identification of variants of such genes that are preferable from the standpoint of selection will allow, apart from the conventional selection of animals, to perform selection at the level of deoxyribonucleic acid technologies, i.e. according to genotype. The paper includes the study of milk productivity indicators and physicochemical quality indicators of milk from cows of Simmental and Alatau breeds by loci of the kappa casein gene, and also determines the cheese suitability and technological properties of milk of cows of Simmental and Alatau breeds with different genotypic affiliations for kappa casein for the production of semi-hard cheeses. The determination of polymorphism by the kappa casein gene was carried out with the use of the polymerase chain reaction method for genotyping of the major milk proteins of kappa casein gene. In a comparative aspect, the interrelation of genotypes with milk productivity was studied, the frequencies of allelic polymorphism of cows of Simmental and Alatau breeds in the Republic of Kazakhstan were identified, the nature of milk productivity was determined for each genotype. Scientifically based data on the assessment of biological value, technological properties, cheese suitability of milk of cows of Simmental and Alatau breeds are obtained.

Prevalence of bovine leukemia in 1983-2019 in China: A systematic review and meta-analysis

Bovine leukemia is a chronic, progressive, contagious tumor disease characterized by malignant lymphoid cell hyperplasia and systemic lymphadenopathy, and is caused by bovine leukemia virus (BLV). The disease affects almost all countries and regions where livestock are raised, and may even be a potential zoonotic disease. Monitoring and early prevention of bovine leukemia is very important. Therefore, we conducted this meta-analysis, the first of its type in the country, to estimate the prevalence of bovine leukemia in 1983-2019 in China. We included a total of 35 publications reported in 1983-2019 from the PubMed, ScienceDirect, Chinese Web of Knowledge (CNKI), VIP Chinese, and Wan Fang databases. In those articles, a total of 34,954 cattle had been tested, of which 4701 were positive for BLV infection. The estimated pooled BLV prevalence was 10.0% (4701/34,954). Subgroup analysis showed that there were significant differences for sampling years, detection methods, and age. BLV prevalence was highest in the following subgroups: sampled before 1985 (38.5%, 437/1134), age 3-5 years (22.5%, 231/1044), and detected by PCR (17.9%, 1228/5100). Regarding geographic factors, there were significant differences in the latitude and elevation subgroups. BLV prevalence was lowest in the subgroups of 20-30° latitude (3.3%, 255/5069) 200-1000 m altitude (2.2%, 560/11,990). We also analyzed other subgroups such as region, variety, breeding method, precipitation, humidity, and temperature, however, the differences were not significant. Our research indicated that the BLV was still prevalent in some of areas in China. We recommend strengthening the testing of cattle aged >1 year and using flexible testing methods such as PCR to control the prevalence of bovine leukemia and to prevent persistent infection.

Detection and molecular characterization of bovine leukemia virus in beef cattle presented for slaughter in Egypt

Bovine leukemia virus (BLV) is the etiological agent of enzootic bovine leukosis, the most common neoplastic disease of cattle worldwide and a serious problem for the cattle industry. Previous studies have shown the molecular prevalence of BLV and the coexistence of BLV genotype-1 and -4 in Egyptian dairy cattle; however, the molecular characteristics of BLV in Egyptian beef cattle are unknown. Therefore, we collected blood samples of 168 beef cattle from slaughterhouses in three governorates in Egypt. Based on BLV-CoCoMo-qPCR-2 targeting long terminal repeats and nested PCR targeting the env-gp51 gene, the BLV provirus infection rates were found to be 47/168 (28.0%) and 42/168 (25.0%), respectively. Phylogenetic analysis based on 501 bp of the BLV env-gp51 gene from 42 BLV isolates revealed that at least six distinctive strains (b, e, f, g, x, and z) were prevalent in cattle across the examined regions. Furthermore, phylogenetic analysis of the 420 bp sequence of the BLV env-gp51 region of the six strains against 11 known genotypes showed that the strains b, e, f, and g were clustered into genotype-1, and strains x and z were clustered into genotype-4. Our results also indicated that strains b and x exist in both dairy and beef cattle in Egypt. The present study is the first to detect and genotype BLV among beef cattle in Egypt.

Seroprevalence and risk factors associated with bovine leukemia virus (BLV) seropositivity in cattle herds from Ecuador

Background: Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukosis (EBL). This disease mainly affects cattle, causing severe economic losses to producers. Objective: To establish individual and herd seroprevalence and determine the risk factors associated with BLV seropositivity for dairy and dual-purpose cattle herds in Ecuador. Methods: A total of 2,668 serum samples from 386 herds were collected. A questionnaire, including variables related to cattle health, management and the environment was completed by each herd. A commercial blocking enzyme-linked immunosorbent assay (ELISA) test was used to determine seropositivity. A generalized estimating equation model (GEE) was developed to determine the factors associated with BLV seropositivity. Results: Individual seroprevalence of BLV infection in Ecuador was 17.3% (CI95% = 15.86-18.74%). Herd prevalence was 37.8% (CI95% = 33.0-42.6%), and intra-herd prevalence ranged between 12.5 and 100% (median: 37.5%). The risk factors associated with BLV seropositivity were artificial insemination (OR: 2,215; CI95% = 1.402-3.501), concrete floors (OR: 2.178; CI95% = 1.217-3.889), presence of wild ruminants (OR: 2.998; CI95% = 1.788-5.027), and sampling season (wet; OR: 1.996; CI95% = 1.140-3.497). Conclusions: Results indicate that BLV is widespread in cattle herds in Ecuador. In addition, the study suggests that a control program to fight BLV infection should focus on controlling the risk factors identified.

Development and implementation of a risk assessment and management program for enzootic bovine leukosis in Atlantic Canada

Over the past 30 yr, the prevalence of bovine leukemia virus (BLV) infection has increased in North America, including Atlantic Canada, at both the herd and individual cow levels. This has occurred despite increased awareness of the disease and its deleterious effects and despite implementation of management practices aimed at reducing disease transmission. Our objectives were to identify risk factors associated with the within-herd prevalence of BLV-infected cows by using a risk assessment and management program workbook, as well as to determine the current level of BLV prevalence in the Atlantic Canada region. We hypothesized that previously established risk factors, including management practices associated with calf rearing and fly control, would affect within-herd BLV prevalence. Bulk tank milk (BTM) samples were collected in January and April of 2016 and again during the same months in 2017 and 2018 from all dairy farms shipping milk in the region. Samples were tested with ELISA for levels of anti-BLV antibodies to estimate within-herd prevalence. Regional BLV prevalence at the herd level was 88.39% of dairy herds infected in 2016 and 89.30% in 2018. All dairy farms shipping milk and who had BTM samples collected in 2017 (n = 605) were eligible to participate in the risk assessment and management program questionnaire (RAMP), which was developed and distributed to all bovine veterinarians in Atlantic Canada. One hundred and six RAMP were returned, with representation from all 4 provinces. The RAMP results were combined with the mean BTM ELISA results, and univariable logistic regression followed by multivariable logistic regression was performed to investigate the association between RAMP risk factors and the estimated within-herd BLV prevalence. Factors in the multivariable model significantly associated with the odds of a herd being classified as >25% estimated within-herd prevalence included history of diagnosis of clinical BLV and calves receiving colostrum from cows with unknown BLV status. Differences in within-herd prevalence were not associated with hypodermic needle and injection practices, rectal sleeve practices, or using bulls for natural breeding, based on these 106 dairy farms.

Visualizing bovine leukemia virus (BLV)-infected cells and measuring BLV proviral loads in the milk of BLV seropositive dams

Bovine leukemia virus (BLV) infects cattle and causes serious problems for the cattle industry, worldwide. Vertical transmission of BLV occurs via in utero infection and ingestion of infected milk and colostrum. The aim of this study was to clarify whether milk is a risk factor in BLV transmission by quantifying proviral loads in milk and visualizing the infectivity of milk. We collected blood and milk from 48 dams (46 BLV seropositive dams and 2 seronegative dams) from seven farms in Japan and detected the BLV provirus in 43 blood samples (89.6%) but only 22 milk samples (45.8%) using BLV-CoCoMo-qPCR-2. Although the proviral loads in the milk tended to be lower, a positive correlation was firstly found between the proviral loads with blood and milk. Furthermore, the infectivity of milk cells with BLV was visualized ex vivo using a luminescence syncytium induction assay (LuSIA) based on CC81-GREMG cells, which form syncytia expressing enhanced green fluorescent protein (EGFP) in response to BLV Tax and Env expressions when co-cultured with BLV-infected cells. Interestingly, in addition to one BLV-infected dam with lymphoma, syncytia with EGFP fluorescence were observed in milk cells from six BLV-infected, but healthy, dams by an improved LuSIA, which was optimized for milk cells. This is the first report demonstrating the infectious capacity of cells in milk from BLV-infected dams by visualization of BLV infection ex vivo. Thus, our results suggest that milk is a potential risk factor for BLV vertical spread through cell to cell transmission.

Simultaneous evaluation of diagnostic marker utility for enzootic bovine leukosis

BACKGROUND

Enzootic bovine leukosis (EBL) is a disease of cattle caused by bovine leukemia virus (BLV). More than 60% of BLV-infected cattle remain subclinical and are thus referred to as aleukemic (AL) cattle. Approximately 30% of infected cattle show a relatively stable increase in the number of B lymphocytes; these cattle are termed persistent lymphocytosis (PL) cattle. A small percentage of infected cattle develop BLV-induced B cell lymphoma (EBL) and are called EBL cattle. Due to the increase in the number of BLV-infected cattle, the number of EBL cattle has featured a corresponding increase over recent years in Japan. Several diagnostic criteria for EBL (e.g., enlarged superficial lymph nodes, protrusion of the eye, increased peripheral blood lymphocyte, etc.) are used for on-farm diagnosis and antemortem tests at slaughterhouses. Since the slaughter of EBL cattle for human consumption is not allowed, on-farm detection of EBL cattle is important for reducing the economic loss incurred by farms. Therefore, establishing new diagnostic markers to improve the efficiency and accuracy of the antemortem detection of EBL cattle is a critical, unmet need. To simultaneously evaluate the utility of candidate markers, this study measured the values of each marker using the blood samples of 687 cattle with various clinical statuses of BLV infection (EBL, PL, AL and non-infected cattle).

RESULTS

Sensitivity (Se) and specificity (Sp) were highest for the serum thymidine kinase (TK) followed by the serum lactate dehydrogenase (LDH) isozyme 2. The number of peripheral blood lymphocytes and proviral load in peripheral blood had the lowest Se and Sp. The values of all markers other than TK were influenced by the sex of the tested cattle.

CONCLUSIONS

Although tLDH and its isozymes (LDHs) may be influenced by the sex of the tested cattle, the high accuracy of TK and LDH2 as well as accessibility and simplicity of the protocol used to measure these enzymes recommend the utility of TK and LDHs for EBL cattle detection. Using these markers for screening followed by the application of existing diagnostic criteria may improve the efficiency and accuracy of EBL cattle detection on farms, thereby contributing to the reduction of economic losses in farms.

Transcriptional activation of long terminal repeat of bovine leukemia virus by bovine heat shock factor 1

Bovine leukemia virus (BLV) causes enzootic bovine leukosis (EBL). The BLV genome encodes Tax protein, a transcriptional activator of viral gene expression that binds to the BLV long terminal repeat (LTR). Heat shock factor 1 (HSF1) is a known regulator of the heat shock response proteins, including heat shock proteins. In the present study, the BLV LTR was investigated for interaction of heat shock element (HSE) with HSF1 and the viral Tax protein. It could be confirmed that a functional HSE is well conserved in different BLV strains. The LTR transcriptional activity, as measured by luciferase reporter assay, was upregulated by bovine HSF1 - without Tax expression - in feline CC81 cells. The HSF1 activated LTR transcription by binding to the HSE. LTR-activation was lost upon HSE removal from the LTR and upon expression of a mutant HSF1 lacking the DNA-binding domain. We conclude that BLV LTR is activated to a basal level by host transcriptional factor HSF1, but without Tax protein involvement.