Prevalence of bovine leukemia virus infection in Florida

A serologic study was undertaken to determine the prevalence of bovine leukemia virus (BLV) infection in dairy and beef cattle in Florida. Using the agar gel immunodiffusion test with a glycoprotein antigen 47.8% of 7,768 dairy cattle and 6.7% of 4,911 beef cattle were found to have antibodies to BLV. The prevalence of BLV antibodies increased significantly (P less than 0.0001) with increasing age. After data were adjusted for age, prevalence of BLV antibodies was significantly associated with dairy breed (P less than 0.05) but not with species (Bos taurus and B indicus) or sex.     

Seroprevalence of bovine immunodeficiency virus and bovine leukemia virus in dairy and beef cattle in hokkaido

Serological survey of bovine immunodeficiency virus (BIV) and bovine leukemia virus (BLV) infection was conducted in dairy cattle from 10 different regions of Hokkaido, Japan. Among 390 cattle, 11.0% of cattle were BIV-seropositive and 3.3% were BLV-seropositive. Moreover, in two dairy farms, where bovine leukosis has been reported, prevalence of BIV infections were 6.4 and 9.1%, respectively. In contrast, among 150 beef cattle, 16.6% were BIV-seropositive while none was BLV-seropositive. Dual infections with BLV and BIV in dairy cattle were tested by using 107 BLV-seropositive sera, and 20 sera were found BIV-positive (18.7%). These results indicate that BIV infection was widespread in Hokkaido.     

Host immune responses in the course of bovine leukemia virus infection

Bovine leukemia virus (BLV) is a type C retrovirus infecting bovine B cells and causing enzootic bovine leukosis. Since it takes long periods to develop the disease, it is believed that BLV and host immune responses are closely related. In this review, the accumulated data showing close relationship between BLV and host immune responses are summarized in 4 sections. First, we discuss the role of cell-mediated immunity in protecting hosts from BLV infection. Second, several reports showing the relationship between the disease progression and the change of cytokine profiles are summarized. In the third section, we have focused on tumor necrosis factor alpha (TNFalpha) and its two types of receptors, and the possible involvement of TNFalpha in the BLV-induced leukemogenesis is discussed. The expression of TNFalpha has been shown to be regulated by major histocompatibility complex (MHC) haplotype. The resistance to BLV infection is supposed to be established by some innate factors, which are closely related to MHC haplotype. Finally, we propose that a breeding strategy based on the MHC haplotype could be a good approach to control BLV infection. This review includes some recent data from us and other groups.     

大庆市某牧场牛白血病病毒感染情况调查

[目的]了解大庆市某牧场牛白血病病毒（BLV）感染情况。[方法]随机选取大庆市某规模化牧场泌乳期奶牛107头,采用ELISA方法进行BLV血清流行病学调查,并采用荧光定量PCR方法加以验证。[结果]ELISA检测结果阳性率为31.78%（34/107）,荧光定量PCR检测结果阳性率为37.38%（40/107）,两种检验方法的阳性重合率为85.00%;BLV高载量牛占总数的26.17%,低载量牛占总数的11.21%。[结论]调查结果表明,该牧场奶牛存在一定程度的BLV感染,在牛群中传播的风险较高。     

Seroprevalence of bovine leukemia virus (BLV) infection in dairy cattle in Isfahan Province, Iran

Bovine leukemia virus (BLV), the causative agent of enzootic bovine leukosis (EBL) is an exogenous C-type oncovirus in the Retroviridae family. It causes significant economic losses associated with the costs of control and eradication programs due to carcass condemnation at slaughter and restrictions of export of cattle and semen to importing countries. The main objective of this research was to determine the seroprevalence of BLV infection in cattle herds in central region of Iran (Isfahan province) using a commercial enzyme-linked immunosorbent assay (ELISA) to detect serum antibodies against BLV. Samples of blood serum were collected from 403 female dairy cattle (Holstein-Friesian) from 21 livestock farms and 303 animals (81.9%) were BLV seropositive. A significant association was found between age as a potential risk factor and BVL seroprevalence with animals ≥ 4 years (86.6%) having a significantly (χ(2) = 35.6, p < 0.001) higher seroprevalence compared to those < 4 years (54.2%). We found no significant statistical association between seroprevalence and pregnancy, lactation status and farming systems as potential risk factors in this study (p > 0.1). It is concluded that BLV infection is a very common problem in the study area. Hence, control measures should be instituted to combat the disease and further studies are required to investigate the impact of this disease on dairy production in the country.     

The recent prevalence of bovine leukemia virus (BLV) infection among Japanese cattle

A seroepidemiological survey of bovine leukemia virus (BLV) infection was conducted in Japan in 2007 using an enzyme-linked immunosorbent assay (ELISA) and an agar gel immunodiffusion (AGID) test. A total of 5420 cattle (dairy, 3966; breeding beef, 797; fattening beef, 657) from 209 farms in seven prefectures in Japan were tested. The overall prevalence of BLV infection was 28.6%. The prevalence of BLV infection in dairy cattle (34.7%) was higher than for both fattening beef cattle (7.9%) and breeding beef cattle (16.3%). Age-specific prevalence showed that BLV prevalence increased with age in all types of cattle and was notably different between dairy and beef cattle under 1 year of age. Among 207 farms, 141 herds (68.1%) had one or more positive animals. The proportion of these positive farms was significantly higher among dairy farms (79.1%) than among beef breeding farms (39.5%) and beef fattening farms (51.9%) (P < 0.001). Dairy farms (40.5%) also showed a significantly higher within-herd prevalence than beef breeding (27.4%) and fattening (14.9%) farms (P = 0.001). This study indicated that BLV is more widely spread in dairy cattle than in beef breeding cattle in Japan. Given the prevalence of BLV infection in dairy and beef cattle was 8- and 1.7-fold higher, respectively, than rates previously found in 1980–1982, BLV appears to be spreading particularly among the dairy cattle population during the last two decades. Further investigation is required to determine the risk factors necessary to control BLV infection that take into account the different farming practices that exist between dairy and beef sectors.     

Horizontal transmission and phylogenetic analysis of bovine leukemia virus in two districts of Miyazaki,Japan

Horizontal transmission is recognized as a major infection route for bovine leukemia virus (BLV), and cattle with high viral loads are considered to be a major infectious source in a herd. However, a correlation between viral loads and the risk of infection has been insufficient to use as a foundation for BLV control strategies. In this report, we examined the epidemiology of BLV infection and the infectious source in a local area. In 2013–2014, BLV infection was investigated in 1,823 cattle from 117 farms in two adjacent districts, Miyazaki, Japan. Seropositive samples for BLV were detected with 88 cattle and in 14 farms. Phylogenetic analysis revealed that 94% of the isolates clustered into genotype I and the remaining isolate into genotype III. Among genotype I, genetically distinct strains were spread at each farm, and cattle infected with less than 3 copies/100 cells did not transmit BLV to other cattle for more than thirty months. This is the first report of concrete data of viral load in relation to viral horizontal transmission under the field condition. The data facilitate farmers and veterinarians understanding the status of BLV infected cattle. This research contributes to BLV infection control and the development of effective BLV eradication programs.     

Lack of TNF alpha supports persistence of a plasmid encoding the bovine leukaemia virus in TNF(-/-) mice

Tumour necrosis factor (TNF) is well recognised for its role in mediating innate immune responses. However, the mechanisms of TNF that influence the adaptive immune response to viral infections are poorly understood. Over recent years, there has been evidence to suggest a role for TNF in the early phase of infection of ruminants with bovine leukaemia virus (BLV). In this study, we infected TNF(-/-) mice with a plasmid encoding infectious BLV to further elucidate the role of TNF in BLV infection. TaqMan quantitative PCR showed that proviral DNA was present in genomic DNA isolated from spleen cells of TNF(-/-) mice 4 weeks post-infection, whereas it was not detected in wild-type mice. We were not able to detect differences in serum IgM or IgG levels between the TNF(-/-) and wild-type mice, or antibodies to BLV after this short period. In showing that the lack of TNF enables the plasmid encoded BLV to persist longer, and therefore rendering the mice more susceptible to an infection with BLV, the data suggest an important defence function of TNF in the early phase of BLV infection.     

Increase of cells expressing PD-L1 in bovine leukemia virus infection and enhancement of anti-viral immune responses in vitro via PD-L1 blockade

ABSTRACT: The inhibitory receptor programmed death-1 (PD-1) and its ligand, programmed death-ligand 1 (PD-L1) are involved in immune evasion mechanisms for several pathogens causing chronic infections. Blockade of the PD-1/PD-L1 pathway restores anti-virus immune responses, with concomitant reduction in viral load. In a previous report, we showed that, in bovine leukemia virus (BLV) infection, the expression of bovine PD-1 is closely associated with disease progression. However, the functions of bovine PD-L1 are still unknown. To investigate the role of PD-L1 in BLV infection, we identified the bovine PD-L1 gene, and examined PD-L1 expression in BLV-infected cattle in comparison with uninfected cattle. The deduced amino acid sequence of bovine PD-L1 shows high homology to the human and mouse PD-L1. The proportion of PD-L1 positive cells, especially among B cells, was upregulated in cattle with the late stage of the disease compared to cattle at the aleukemic infection stage or uninfected cattle. The proportion of PD-L1 positive cells correlated positively with prediction markers for the progression of the disease such as leukocyte number, virus load and virus titer whilst on the contrary, it inversely correlated with the degree of interferon-gamma expression. Blockade of the PD-1/PD-L1 pathway in vitro by PD-L1-specific antibody upregulated the production of interleukin-2 and interferon-gamma, and correspondingly, downregulated the BLV provirus load and the proportion of BLV-gp51 expressing cells. These data suggest that PD-L1 induces immunoinhibition in disease progressed cattle during chronic BLV infection. Therefore, PD-L1 would be a potential target for developing immunotherapies against BLV infection.     

Characterization of immune responses caused by bovine leukemia virus envelope peptides in sheep.

To study the immunomodulative activity caused by bovine leukemia virus envelope (BLV Env) peptide, sheep were immunized with two kinds of Th-epitope peptides, peptide 98 (BLV Env 98-117), and 61 (BLV Env 61-78). Four of eight immunized sheep showed specific proliferative responses against both of the peptide stimulations. To characterize the cells responding to the peptides, peptide-specific cells were established from the responding sheep by the continuous stimulation of peripheral blood mononuclear cells (PBMCs) with either peptide 98 or 61 in vitro. The peptide 98-specific cells consisted of CD4-positive cells, whereas the peptide 61-specific cells consisted of CD8-positive cells and MHC class II-positive cells. In addition, cytokine profile analysis indicated that the peptide 98-stimulated cells expressed IFN-gamma but not IL-10, although the peptide 61-stimulated cells expressed IL-10 but not IFN-gamma. These results show that BLV envelope peptides 98 and 61 can modulate immune responses of sheep lymphocytes in different ways and may contribute to the pathogenesis of BLV infection.     

Effects of bovine leukemia virus infection on milk neutrophil function and the milk lymphocyte profile

The effects of bovine leukemia virus (BLV) on the immune response have been extensively investigated; however, its effects on mammary gland immunity are only speculative. Although BLV has a tropism for B cells, it can affect both adaptive and innate immunities because these systems share many effector mechanisms. This scenario is the basis of this investigation of the effects of BLV on mammary gland immunity, which is largely dependent upon neutrophilic functions. Thus, the present study sought to examine neutrophilic functions and the lymphocyte profile in the milk of naturally BLV-infected cows. The viability of the milk neutrophils and the percentage of milk neutrophils that produced reactive oxygen species (ROS) or phagocytosed Staphylococcus aureus were similar between BLV-infected and BLV-uninfected dairy cows. Furthermore, the expression of CD62L and CD11b by the milk neutrophils and the percentage of milk neutrophils (CH138⁺ cells) that were obtained from the udder quarters of the BLV-infected cows were not altered. Conversely, the median fluorescence intensity (MFI) representing intracellular ROS production and the phagocytosis of S. aureus, the expression of CD44 by the milk neutrophils and the percentage of apoptotic B cells were lower in the milk cells from BLV-infected dairy cows, particularly those from animals with persistent lymphocytosis (PL). The lymphocyte subsets were not different among the groups, with the exception of the percentage of CD5⁻/CD11b⁻ B cells, which was higher in the milk cells from BLV-infected cows, particularly those with PL. Thus, the present study provides novel insight into the implications of BLV infection for mammary gland immunity.     

Suppression of immunological responses in rabbits experimentally infected with bovine leukemia virus

Ten 2- to 4-month-old rabbits were inoculated subcutaneously with bovine leukemia virus (BLV)-infected bovine or sheep cells. By 6 weeks after inoculation all ten rabbits had converted to BLV antibody-positive, and BLV or BLV antigen was detected in lymphocytes from most of the rabbits tested, although there were few antigen-producing cells. Three rabbits showed continuous respiratory symptoms after infection and one died with pneumonia. Humoral immune responses against mouse serum were significantly suppressed in BLV-infected rabbits compared with non-infected control rabbits. The lymphocyte blastogenesis response was also suppressed in BLV-infected rabbits. At the time of necropsy, six rabbits showed pulmonary lesions; however, none of the BLV-infected rabbits had tumors during an observation period of over 1 year.     

Seroprevalence of bovine immunodeficiency virus in dairy and beef cattle herds in Korea.

Infection of bovine immunodeficiency virus (BIV), a lentivirus, is thought to sporadically occur throughout the world, but seroepidemiological surveys concerning the incidence of BIV are limited and have not been undertaken in Korea. A total of 266 sera from different twenty dairy (Holstein) and twenty-six Korean native beef (Hanwoo) farms of the south-western part of Korea was analyzed for the presence of anti-BIV antibodies by Western blotting. Thirty five percent and 33% of dairy and beef cattle, respectively, were BIV-seropositive. By nested polymerase chain reaction, it was confirmed that these seropositive cows had provirus in the peripheral blood mononuclear cells. To demonstrate the correlation with BIV and bovine leukemia virus (BLV) infection, these sera were also analyzed for anti-BLV antibodies by immunodiffusion test, resulting in high prevalence of BLV infection but relatively a few dual infections. We report herein the first serological detection of antibodies to BIV in Korea.     

Transmission of bovine leukemia virus by Tabanus fuscicostatus

Bovine leukemia virus (BLV) was transmitted by horse flies, Tabanus fuscicostatus, from a cow with a lymphocyte count of 31,500/mm3 to goats and dairy calves. As few as 10 and 20 flies transmitted BLV to goats and calves respectively, but the minimal number of flies required to transmit the infection was not established. Groups of 150 and 100 T fuscicostatus transmitted BLV to beef calves from a cow with a lymphocyte count of 14,600/mm3. These results support a role for horse flies in the horizontal transmission of BLV.     

Antioxidant status and biomarkers of oxidative stress in bovine leukemia virus-infected dairy cows

Bovine leukemia virus (BLV) is among the most widespread livestock pathogens in many countries. Despite advances in understanding the pathogenesis of this disease, little is known about the involvement of oxidative stress. Therefore, this study examined the antioxidant status and the markers of oxidative stress in BLV-infected dairy cows. BLV infection was associated with an increase in triacylglycerol levels, a decrease in glutathione peroxidase (GSH-Px) activity and a tendency toward lower superoxide dismutase activity in the infected animals. No significant difference was observed in other markers of oxidative stress (i.e., conjugated dienes, hydroperoxides and malondialdehyde) in the infected animals compared to controls. A novel method for the analysis of oxidative stress, Z-scan based on the measurement of the mean-value of θ in low density lipoprotein indicated that the infected animals had low-density lipoprotein particles that were slightly less modified than those from the healthy group. Thus, we conclude that BLV infection is associated with a selective decrease in GSH-Px activity without any alteration in the common plasma markers of oxidative stress.     

Seroprevalence of Mycobacterium avium subspecies paratuberculosis, Neospora caninum, Bovine leukemia virus, and Bovine viral diarrhea virus infection among dairy cattle and herds in Alberta and agroecological risk factors associated with seropositivity

A province-wide, cross-sectional seroprevalence and agroecological risk factor study of Mycobacterium avium subspecies paratuberculosis (MAP), Neospora caninum (NC), Bovine leukemia virus (BLV), and Bovine viral diarrhea virus (BVDv) genotypes 1 and 2 (BVDv1 and BVDv2) infection in dairy cattle herds in Alberta was conducted. Among adults, the seroprevalence of MAP, NC, and BLV was 9.1%, 18.5%, and 26.9%, respectively. For MAP, based on a herd test cutpoint of 2 or more seropositive cows, 58.8% of herds were infected. Herd-level seroprevalence for NC and BLV was 98.7% and 86.7%, respectively, based on a herd-test cutpoint of 1 seropositive cow. Among unvaccinated dairy heifers, the seroprevalence for BVDv1 and BVDv2 infection was 28.4% and 8.9%, respectively, while herd-level infection was 53.4% and 19.7%. Seroprevalence for MAP varied moderately by agroecological region, whereas that for NC, BLV, and BVDv1 and BVDv2 did not. For MAP, aridity and soil pH (correlated features of the region) were also important.     

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.     

Economic implications of bovine leukemia virus infection in mid-Atlantic dairy herds

OBJECTIVE: To determine the baseline costs of bovine leukemia virus (BLV) infection, including costs of clinical disease and subclinical infection, in a dairy herd representative of the mid-Atlantic region and compare these costs with the cost of a test-and-manage BLV control program. DESIGN: Stochastic spreadsheet model. SAMPLE POPULATION: A commercial Holstein dairy herd with 100 milking cows. PROCEDURES: A spreadsheet model was developed. The overall cost of infection included the cost of clinical disease (ie, lymphosarcoma [LS]) and the effects of subclinical infection on milk production and premature culling. Model input values and distributions were designed to reflect economic conditions in the mid-Atlantic region. Relative costs of infection and control were calculated for infection prevalences of 20, 50, and 80%. RESULTS: Estimated mean cost to the producer per case of LS was 412 dollars; for a herd with a 50% prevalence of BLV infection, annual incidence of LS was 0.66. Mean annual cost of subclinical infection at a 50% prevalence of infection was 6,406 dollars. Mean annual cost of a test-and-manage control program was 1,765 dollars. The cost of clinical disease and subclinical infection varied substantially with the prevalence of infection, whereas the cost of control varied with herd size. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that a basic BLV control program may be economically beneficial in herds in which the prevalence of BLV infection is > or = 12.5%. Farm-specific considerations may factor prominently when weighing the costs and benefits of an individual BLV control program.     

Increased bovine Tim-3 and its ligand expressions during bovine leukemia virus infection

ABSTRACT: The immunoinhibitory receptor T cell immunoglobulin domain and mucin domain-3 (Tim-3) and its ligand, galectin-9 (Gal-9), are involved in the immune evasion mechanisms for several pathogens causing chronic infections. However, there is no report concerning the role of Tim-3 in diseases of domestic animals. In this study, cDNA encoding for bovine Tim-3 and Gal-9 were cloned and sequenced, and their expression and role in immune reactivation were analyzed in bovine leukemia virus (BLV)-infected cattle. Predicted amino acid sequences of Tim-3 and Gal-9 shared high homologies with human and mouse homologues. Functional domains, including tyrosine kinase phosphorylation motif in the intracellular domain of Tim-3 were highly conserved among cattle and other species. Quantitative real-time PCR analysis showed that bovine Tim-3 mRNA is mainly expressed in T cells such as CD4+ and CD8+ cells, while Gal-9 mRNA is mainly expressed in monocyte and T cells. Tim-3 mRNA expression in CD4+ and CD8+ cells was upregulated during disease progression of BLV infection. Interestingly, expression levels for Tim-3 and Gal-9 correlated positively with viral load in infected cattle. Furthermore, Tim-3 expression level closely correlated with up-regulation of IL-10 in infected cattle. The expression of IFN-γ and IL-2 mRNA was upregulated when PBMC from BLV-infected cattle were cultured with Cos-7 cells expressing Tim-3 to inhibit the Tim-3/Gal-9 pathway. Moreover, combined blockade of the Tim-3/Gal-9 and PD-1/PD-L1 pathways significantly promoted IFN-γ mRNA expression compared with blockade of the PD-1/PD-L1 pathway alone. These results suggest that Tim-3 is involved in the suppression of T cell function during BLV infection.