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.

Comparison of PLA with AGID and ELISA results in serology diagnosis of bovine leukosis

The aim of this study was to assess the diagnostic value of Peroxidase Linked Assay (PLA) for detecting the bovine leukemia virus (BLV) infection. Two negative and two positive reference sera were applied to 204 serum samples from dairy cows from 3 different farms (I, II and III). The best results of serological testing were obtained in the herd infected with BLV for several years (I). Amongst 10 serum samples taken at random, all were positive in AGID, ELISA and PLA. Serological tests of samples from group II revealed: 34 (73.9%) positive results in AGID and 39 (84.7%) either in ELISA or PLA. In group III positive results in AGID occured in 81.8% of cases, and 91.9% and 92.9% in ELISA and PLA respectively. The mean OD value for positive samples in groups II and III ranged between 0.943 and 0.215. Immunoperoxidase PLA is a specific and sensitive test for detection of BLV infections.

The improvement of monitoring methods of cattle infection with bovine leukemia virus (BLV)

This study demonstrates the usefulness of PLA and nested-PCR methods for the detection of cattle infection with enzootic bovine leukemia virus. Serological control with PLA was by 1.7% more sensitive than reference ELISA examination. Both the DNA of env-BLV gene in NCR, V-NCR, FLK and in recombinated AG clone cells, as well as in the whole blood and in blood isolated leukocytes of dairy cattle, were detected with the nested-PCR.

The eradication of enzootic bovine leucosis in a large farm population

In the years 1992 to 2002 the ID and ELISA systemic serological examinations of infected cows from a large farm brought advantageous results. A total of 468 cows from three farms from Opole province were examined. In the years 1997 to 2002 there were four times more positive serological results obtained than in the years 1992 to 1996. The elimination of BLV infected animals from farms and watering of serologically negative calves with milk substitute feed were very useful methods. In the year 2002 the control of all cattle gave negative ELISA results based on anti-gp51 monoclonal antibodies. The farm demonstrated BLV-free status after 10 years as a result of regular laboratory testing and successful elimination of all positive animals.

Detection of bovine leukemia virus in blood and milk by nested and real-time polymerase chain reactions

Concerns about retroviruses in livestock and products derived from them have necessitated the development of tests to detect the bovine leukemia virus (BLV) in blood and milk from cattle. Dairy cattle (n = 101) from 5 different geographical areas were used for this study. A nested polymerase chain reaction (PCR) identified 98% of BLV seropositive cattle (n = 80) from blood and 65% from milk, whereas real-time PCR detected 94% of BLV seropositive cattle from blood and 59% from milk. Bovine leukemia virus was also detected by PCR in approximately 10% of seronegative cattle (n = 21), most likely because of early detection before seroconversion.

[Use of diagnostic DNA probes for detection of the provirus of bovine leukemia virus in infected cows]

A method of detection of BLV proviral DNA in the peripheral blood leukocytes of cattle is reported. Leukocytes were used without preliminary cultivation. Cell DNA was dot-hybridized with P-labeled plasmid containing a fragment of BLV proviral DNA. The sera samples taken from the cattle under study were also tested using immunodiffusion assay (ID). The results of comparison showed that dot-hybridization assay is a more sensitive diagnostic test than ID, because it detects BLV infection in apparently normal cattle, which was seronegative in ID.

Direct production losses and treatment costs from bovine viral diarrhoea virus, bovine leukosis virus, Mycobacterium avium subspecies paratuberculosis, and Neospora caninum

Our purpose was to determine direct production losses (milk loss, premature voluntary culling and reduced slaughter value, mortaliy loss, and abortion and reproductive loss) and treatmetn costs (veterinary services, medication cost, and extra farm labour cost) due to four infectious diseases in the maritime provinces of Canada: bovine viral diarrhoea (BVD), enzootic bovine leukosis (EBL), Johne's Disease (JD), and neosporosis. We used a partial-budget model, and incorporated risk and sensitivity analyses to identify the effects of uncertainty on costs. Total annual costs for an average, infected, 50 cow herd were: JD$ 2472; BVD$ 2421; neosporosis $ 2304; EBL$ 806. The stochastic nature of the proportion of infected herds and prevalence of infection within a herd were used to estimate probability distributions for these ex post costs. For all diseases, these distributions were right skewed. A sensitivity analysis showed the largest effect on costs was due to milk yield effects. For example, changing milk production loss from 0 to 5% for BVD increased the costs for the disease by 266%.

Management factors related to seroprevalences to bovine viral-diarrhoea virus, bovine-leukosis virus, Mycobacterium avium subspecies paratuberculosis, and Neospora caninum in dairy herds in the Canadian Maritimes

Bovine viral-diarrhoea (BVD), enzootic bovine leukosis (EBL), Johne's disease (JD), and neosporosis lower on-farm productivity, reduce export competitiveness, and increase consumer concerns regarding safety. Our purpose was to examine the relationship between 27 control practices and the estimated true seroprevalences for these four diseases for 2604 cattle in 90 dairy herds in the Maritimes provinces of Canada. Overall, 37.8, 20.4, 3.4, and 19.2% of all sampled cattle were truly exposed to the agents of BVD, EBL, JD, and neosporosis, respectively. The median within-herd true prevalences were 0, 9.3, 0, and 12.3%, respectively. Factor analysis reduced the 27 control practices to two highly correlated factors. Tobit-regression analyses determined that vaccination practices were associated with reduced prevalence of exposure for Bovine viral-diarrhoea and EBL. Also, farms that tended to purchase their dairy animals were associated with higher seroprevalence for Johnes' disease. Neither of these two factors was associated with the seroprevalence of Neospora caninum infection. The few routine biosecurity measures that were investigated in this study were generally not related to the seroprevalences of these farms.

Partial sequencing of env gene of bovine leukaemia virus from Brazilian samples and phylogenetic analysis

Analysis of the partial bovine leukaemia virus (BLV) env gp51 gene sequences obtained from three BLV strains isolated in three different regions of Brazil was carried out. The Brazilian BLV env gp51 sequences were compared with seven other corresponding sequences of BLV strains isolated in different countries and with consensus sequence as well. The obtained data point on qualitative and quantitative differences among the analysed strains as far as the occurrence of single point mutations is concerned. Two Brazilian strains show significantly higher mutation rate than other analysed strains. Amino acid analysis did not show, however, any substantial changes of the primary protein structure coded by well conserved region of BLV env gp51 gene. Based on the obtained data, the putative dendogram image of possible phylogenetic relations among the studied BLV strains is presented as well.

Genetic heterogeneity among bovine leukemia virus genotypes and its relation to humoral responses in hosts

The existence of bovine leukemia virus (BLV) genotypes was investigated by restriction fragment length polymorphism (RFLP) analysis using bovine peripheral blood leukocytes collected from different geographical areas of Japan. For this purpose a nested polymerase chain reaction (PCR) for a 444 bp fragment of the envelope (env) gene was used because it was previously reported that this region might be responsible for the serological status in the host. The PCR products from 60 samples of BLV-infected cells were digested with endonucleases BamH I, Bgl I, Bcl I, Hae III and Pvu II. RFLP analysis demonstrated that there were six different genotypes of BLV present among cattle in Japan. In some herds PCR-positive animals were infected with only one genotype, but in other herds a few genotypes were found. One genotype was dominant throughout infected cattle and it was also detected in neoplastic cells from three of four animals with lymphosarcoma and three cell lines persistently infected with BLV. Production of antibodies to BLV in each cattle was surveyed by agar gel immunodiffusion and indirect hemagglutination tests, and the results were compared with those obtained from PCR. No genotype related to decreased immunoreactivity was detected. The difference in anti-viral immune responses of each animal appears to be related to the infection stage and other host factors, not to genetic heterogeneity of the envelope gene.

Relative sensitivity and specificity of agar gel immunodiffusion, enzyme immunosorbent assay, and immunoblotting for detection of anti-bovine leukemia virus antibodies in cattle

Three serologic methods for the detection of antibodies to bovine leukemia virus (BLV) were compared using the sera of 140 dairy cows. A widely used commercial agarose immunodiffusion screening assay and a commercial antibody capture enzyme immunosorbent assay were compared for sensitivity and specificity with immunoblotting as the standard. The immunoblot utilized the same antigen preparations that were provided in the commercial kits. The agarose immunodiffusion and the enzyme immunosorbent assay were comparable in the number of positive animals detected. However, the commercial screening kits failed to detect 39% (agarose immunodiffusion) and 35% (immunosorbent assay), respectively, of the animals determined serologically positive by immunoblot. These findings corroborate those of some other groups and emphasize the need for more sensitive tests to identify BLV positive cattle for culling or separation in order to create BLV-free herds.

Seroprevalence and molecular evidence for the presence of bovine immunodeficiency virus in Brazilian cattle

Data on the worldwide distribution of bovine immunodeficiency virus (BIV) and bovine leukemia virus (BLV) is limited. A prevalence study of antibodies to BIV and BLV was conducted in six different cattle herds in Brazil. Out of a total of 238 sera analyzed, 11.7% were found positive for anti-BIV p26 antibodies as determined by Western blot analysis, 2.1% were positive for anti-BLV gp51 antibodies as detected by immunodiffusion test. Peripheral blood mononuclear cells from BIV seropositive cattle were found to have BIV-provirus DNA, as detected by nested polymerase chain reaction. A nucleotide sequence corresponding to a 298 bp fragment of the BIV pol gene was also analyzed. Amino acid sequences of these Brazilian pol gene products showed 98.0 to 100% homology to the American strain BIV R29, 97.0 to 99.0% to Japanese BIV isolates, and divergence ranged from 0 to 4.0% among Brazilian BIV isolates. This evidence of the presence of BIV and BLV infections in Brazil should be considered a health risk to Brazilian cattle populations and a potential causative agent of chronic disease in cattle.

The detection of bovine leukemia virus proviral DNA by PCR-ELISA

A sensitive non-radioactive microplate hybridization assay for the detection of proviral DNA of bovine leukemia virus (BLV)-specific polymerase chain reaction (PCR) product is described. The PCR products are labeled by adding digoxigenin-dUTP to the nested PCR reaction and are captured by a microtitre plate coated with oligonucleotide probe, which is complementary to the inner region of the amplification product. Captured products are reacted with an anti-DIG Fab fragment conjugated to peroxidase, and detected using a colorimetric reaction. The PCR-enzyme linked immunosorbent assay (ELISA), detecting as low as 10(-4) ng of proviral DNA in a background of 1 microg of BLV-negative DNA, was up to 100-fold more sensitive than ethidium bromide staining, and showed equal sensitivity to Southern blot hybridization. Using this method it was possible to monitor the presence of proviral DNA in four sheep infected experimentally with BLV, over a 10 months postinfection period, as well as in 29 cattle infected naturally. The test is rapid and highly sensitive and is a useful additional tool for the detection of BLV-infected animals.

Seroprevalence of bovine leukemia virus in dairy cattle in Argentina: comparison of sensitivity and specificity of different detection methods

Bovine leukemia virus (BLV) is a retrovirus that induces a chronic infection in cattle, which develop in three possible pathological forms: asymptomatic course, persistent lymphocytosis (PL) and lymphosarcoma. Once infected, cattle remain virus carriers for life and start to show a serological reaction within a few weeks after infection. Eradication and control of the disease is based on early diagnostic and segregation of the carriers. The agar gel immunodiffusion (AGID) test has been the serological test of choice for routine diagnosis of serum samples. Nevertheless, in more recent years, the enzyme-linked immunosorbent assay (ELISA) has replaced the AGID for large scale testing. Although Argentina has over 60 million cattle population, no nationwide studies have been conducted yet to determine the prevalence of the infection. To estimate the rate of BLV infection in dairy cattle in Argentina, a survey for specific antibodies in >10,000 serum samples from animals over 18 months old, belonging to 363 different herds from the largest dairy production areas of the country, was carried out in our laboratory, along 1999. For this purpose, we developed an ELISA to detect serum antibodies against the BLV virus. The cut-off of the ELISA was established over 339 serum samples, using polymerase chain reaction and southern blot (PCR-SB) as confirmatory test. The sensitivity and specificity of the ELISA was of 97.2 and 97.5%, respectively, while the local official AGID test showed a sensitivity of 79.7% and specificity of 99.0%. To know the seroprevalence of BLV on dairy herds, and also the incidence of the infection within the herd, the serological survey was based on individual serum samples. The results show that the prevalence of infected individuals is of 32.85%, while the percentage of infected herds, harboring one or more infected animals, is of 84%. These results indicate a medium level of seropositive animals when taken individually, but a high prevalence of infected farms, which has been notoriously increased in the last 15 years as shown when compared with previous data from particular geographic areas, indicating that BLV constitutes a serious sanitary problem for dairy producers in Argentina. They also indicate the poor sensitivity of the official AGID test used in the country.

Delayed emergence of bovine leukemia virus after vaccination with a protective cytotoxic T cell-based vaccine

In a previous study eight MHC class I-matched sheep were vaccinated with a minimal cytotoxic T lymphocyte (CTL) peptide epitope vaccine and were challenged with the retrovirus, bovine leukemia virus (BLV). Half the vaccinated animals remained PCR negative after challenge, whereas the remaining half and the placebo group became PCR positive within 4 weeks postchallenge (Hislop AD, Good MF, Mateo L, Gardner J, Gatei MH, Daniel RCW, Meyers BV, Lavin MF, and Suhrbier A: Nat Med 1998;4:1193). Here we show that neither epitope mutations nor processing differences explained why half the peptide-vaccinated animals failed to resist the BLV challenge. However, in these animals the development of BLV-induced lymphosarcomas was significantly delayed compared with the placebo group, suggesting a role for CTLs in preventing retrovirus-induced cancers. Importantly, two of the initially protected animals become PCR positive after approximately 1.5 years, indicating extended suppression but not elimination of challenge virus by vaccine-induced CTLs. The late emergence of virus could not be explained by epitope escape mutations or the loss of memory CTL responses. We speculate that high levels of effector CTL may be needed to protect animals from a postchallenge viremia and maintenance of such effector CTLs, rather than memory CTLs, may be required to prevent subsequent emergence of virus from latent pools.

Development and evaluation of a highly sensitive and specific blocking enzyme-linked immunosorbent assay and polymerase chain reaction assay for diagnosis of bovine leukemia virus infection in cattle

OBJECTIVE

To develop a blocking ELISA for detection of bovine leukemia virus (BLV) antibodies that is comparable to a radioimmunoprecipitation (RIP) assay, to evaluate use of this ELISA for identification of BLV-infected herds, and to develop a polymerase chain reaction (PCR) assay for direct diagnosis of infection with BLV.

SAMPLE POPULATION

Serum samples and pooled bulk-tank milk samples from cattle.

PROCEDURE

The blocking ELISA was developed, using BLV gp51 as antigen, captured by a selected bovine polyclonal serum. A nested PCR was conducted with primers specific for a segment of the pol region of the BLV genome.

RESULTS

Sensitivity and specificity of the ELISA were comparable to those of the RIP assay. Use of the ELISA on pooled milk samples allowed identification of herds in which prevalence of BLV infection among lactating cows was as low as 2.5%. Pooled milk samples from BLV-free herds did not react in the ELISA. All cattle that had positive results for the nested PCR had BLV antibodies, but cattle with consistantly low antibody titers required examination of sequential DNA samples to detect viral sequences. None of the 63 antibody-negative cattle had positive results for the PCR.

CONCLUSIONS AND CLINICAL RELEVANCE

This ELISA is a highly specific and sensitive assay for the detection of BLV antibodies in serum and milk samples of cattle. Examination of pooled milk samples with the ELISA provides a reliable, practical, and economic procedure for identification of BLV-infected herds. The nested PCR also constitutes a specific procedure for direct diagnosis of infection with BLV.

Comparative study of PCR as a direct assay and ELISA and AGID as indirect assays for the detection of bovine leukaemia virus

The choice of a diagnostic method depends on the characteristics of the herd to be analysed. Two herds with different prevalences of enzootic bovine leukaemia were chosen to study the concordance between agar gel immunodiffusion (AGID), enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) methods. PCR, an increasingly used virological method, was performed with four sets of primers, amplifying different genomic regions (env, pol and tax), from DNA extracted either from peripheral blood monocytes (PBMCs) or milk leucocytes. The highest percentage of positive animals was obtained using PCR performed with DNA extracted from PBMCs using primers which amplified either env or pol, followed by PCR using PBMCs and primers which hybridized with tax, then ELISA using serum and finally AGID. The results of PCR were more consistent with PBMCs than when milk leucocytes were used.

Seroprevalence of bovine immunodeficiency virus and bovine leukemia virus in draught animals in Cambodia

Since bovine immunodeficiency virus (BIV), known as bovine lentivirus, has been detected in dairy and beef cattle in various countries around the world, a prevalence study of antibodies to BIV and bovine leukemia virus (BLV) was conducted in draught animals in five provinces in Cambodia, where protozoan parasite infections were suspected in some animals. To clarify the status of draught animals including Haryana, Brahman, mixed-breed, local breed cattle and muscle water buffaloes, a total of 544 cattle and 42 buffaloes were tested, and 26.3 and 16.7%, respectively, were found positive for anti-BIV p26 antibodies determined by Western blotting. There were 5.3% positive for anti-BLV antibodies detected by immunodiffusion test among the cattle, but no reactors among buffaloes and no dual infection for both BIV and BLV was determined in this study. Peripheral blood mononuclear cells from BIV-seropositive cattle were found to have BIV-provirus DNA, as detected by polymerase chain reaction and subsequent Southern blot hybridization. This is the first evidence for the presence of BIV and BLV infections in draught animals in tropical countries such as Cambodia. This wide distribution of BIV suggests its association with problems in animal health as reported worldwide, and that a primary BIV infection can predispose death of affected animals by other aggressive pathogens or stresses.

An unusual presentation of enzootic bovine leukosis

A 6-year-old, Holstein x Simmental cow diagnosed with pyelonephritis had increasing difficulty rising and became recumbent, despite treatment with antibiotics. A serological test for the bovine leukemia virus was positive; at necropsy, the left kidney and ureter and the myocardium showed lesions of lymphosarcoma, confirmed by histology.

Assessment of bovine leukemia virus transcripts in vivo

Reverse transcriptase PCR (RT-PCR) consistently detected bovine leukemia virus transcripts in fresh cells, and competitive RT-PCR enumerated these transcripts. The detection of transcripts in limited numbers of tumor cells indicated that expression occurs in a minority of cells. The data suggest that individual cells contain hundreds of copies of the tax/rex transcript in vivo.

A case of an embryo transfer calf infected with bovine leukemia virus from the recipient cow

A case was discovered where the embryo transfer (ET) calf had been infected with bovine leukemia virus (BLV) from the recipient cow. The embryo was transferred from the BLV-uninfected donor cow to the recipient cow. However, the BLV test had not been performed to the recipient cow before ET was performed. The ET calf was raised in a calf hatch from birth to 1-month old and was given the recipient cow's colostrum and milk artificially. The ET calf was raised with the two other calves from a 1-month old to a 6-month old. The BLV test was performed to the ET calf by agar gel precipitation (AGP) and passive haemagglutination (PHA) assay when the ET calf was 6 months old. Because the ET calf was positive, the BLV test was performed to the recipient cow, the two other calves raised with the ET calf and the two dams of the two other calves. Because the recipient cow only was positive at the time of the first test, we judged that the ET calf had been infected with BLV from the recipient cow. The importance of the BLV test being carried out on the recipient cow for the prevention of enzootic bovine leukemia in a case of ET was recognised.

Rapid detection of specific polyclonal and monoclonal antibodies against bovine leukemia virus

ELISA and Western blot have been used for detecting specific antibodies or antigens for routine diagnostic laboratory tests and experimental protocols, as well as for screening hybridomas secreting antibodies. Although these techniques are sensitive, some slow growing hybridomas are identified as positive only when they are grown slowly long time. We standardized the dot-ELISA, a more sensitive technique, for the detection of antibodies against BLV. The main advantages of the dot-ELISA described in this study are (a) its sensitivity, detecting hybridomas which would otherwise be considered negative and discarded from the results of indirect ELISA and/or Western blot; and (b) the possibility of economizing reagents using as little as 1 microl of the antigen and 0.5 microl of antibody and conjugate. Different BLV-antigen preparations were bound to nitrocellulose membranes (NC), including cells lysed chemically (LYS) or by sonication (SOC), semi-purified virus (PV), and supernatant from infected cultures, either without treatment (SUP) or sonicated (SOS). The antigen preparations most adequate for detecting monoclonal antibodies against BLV and polyclonal antibodies in cattle sera were undiluted cell lysates (LYS) and semi-purified BLV (PV). When testing bovine sera, the supernatant (SUP) and sonicated supernatant (SOS) antigens gave a high background due to the presence of FCS which reacted with the anti-bovine labeled antibodies. In this study, 59 BLV specific antibody secreting hybridomas were identified using the dot-ELISA, compared to only 20 detected using iELISA, and doubtful reactions due to nonspecific binding to fetal calf serum (FCS) and cellular components were measured. The results of the improved dot-ELISA described may be stored at room temperature for future reference. Results were consistently reproducible in coated nitrocellulose membranes kept at different storage temperatures (-20 degrees C, 4 degrees C, and 25-30 degrees C) 48 h, 1 week and 5 months.

Up-regulation of tumor necrosis factor alpha mRNA is associated with bovine-leukemia virus (BLV) elimination in the early phase of infection

Protective immune responses were analyzed in eight sheep vaccinated with BLV envelope peptides and experimentally infected with bovine-leukemia virus (BLV). Five of eight peptide-immunized sheep showed a high T-cell proliferative response to the BLV peptides and all of these were protected from the infection. The other three peptide-immunized sheep showed no T-cell proliferative responses to any BLV antigens similar to control sheep, though they also exhibited resistance to BLV challenge. To investigate other mechanisms which suppress BLV expansion in these non-responding sheep, we measured the levels of the cytokine expressions before, and after, BLV challenge using competitive reverse-transcriptase polymerase chain-reaction systems. It was revealed that the expression of tumor necrosis factor alpha (TNFalpha) was higher in BLV-resistant sheep than in BLV-susceptible sheep. Thus, TNFalpha expression rather than specific T-cell activity may play an important role in the protective mechanism against BLV infection, at least during the primary viremia phase.