Enzootic bovine leucosis.

Enzootic bovine leucosis is associated with infection by bovine leucosis virus. The incubation period is measured in years and a minority of infected animals develop clinical signs. The disease is widespread in Europe and elsewhere and can cause significant economic loss. The epidemiology is incompletely understood and findings from one cattle production system may not be directly applicable to another. Major control programmes exist in Denmark and West Germany and control schemes are being developed elsewhere. Eradication of enzootic bovine leucosis has been established as a goal in the EEC and research is revealing the ways in which this goal may be attained. To be effective, control and epidemiological monitoring must be interactive. Recently introduced serological tests, of improved sensitivity, provide a valuable tool.     

Lack of sequence variation in sporadic bovine leucosis in regions of tumour suppressor genes p53 and p16

Regions of the promoter and exons 5-8 of the tumour suppressor gene p53 were analysed in 25 cases of sporadic bovine leucosis. The study included 17 cases of juvenile leucosis, five cases of adult leucosis and three cases of skin leucosis. Exon 2 of tumour suppressor gene p16 was also investigated in the same samples. No sequence variations were present in the analysed areas of the genes. In p53, this fact represents a clear difference in comparison with enzootic bovine leucosis. In p16, no comparative data are available.     

用单抗研究T细胞与牛流行性白血病发生的关系

本试验对10头患流行性白血病病牛的不同器官的肿瘤组织，用8种单克隆抗体（McAb),TH14B、BAQ44A、PIg45A、BIg715A、PIg501E、cAct105、MM1A、AHCC125染色进行了观察。结果：病牛经临床病理学和免疫琼扩试验而诊断为EBL，通过免疫组织化学检测，在10个病例中发现有9个病例的肿瘤组织对B细胞属性的McAb有很强的染色反应，证明其来源于B细胞。仅有1个病例对B细胞属性的McAb着色很淡，而对T细胞属性的McAb着色很深，呈强阳性反应，说明其来源可能与T细胞有关。     

Results of veterinary tumor research and their significance for practice]

Enzootic bovine leucosis and Marek's disease of fowl are the most important tumour diseases of farm animals, with the greatest repercussions on the national economy, today. Experimental findings obtained from either disease in recent years are reported in this paper, and an assessment is made of their importance to practice. In the context of enzootic bovine leucosis, particular reference is made to those findings which helped to establish the presence of virus infection, results by which the pathogen could be characterised, and to studies undertaken with the view to devising methods for virologico-serological diagnosis. In the context of Marek's disease, reference is made to virological, epizootiological, and diagnostic aspects, however, with emphasis being laid on possibilities for immunisation and, in that connection, on known fundamental concepts for successful immunoprophylaxis against that tumour disease.     

The reasons for the occurrence of non-specific reactions in the immunodiffusion test for enzootic bovine leukosis

A batch of enzootic bovine leucosis antigen earmarked for immunodiffusion testing exhibited unspecific responses to cattle sera, which prompted an investigation of the underlying causes. Evidence was produced, for the first time ever, that such reactions were attributable to an antigen-antibody reaction caused by Mycoplasma arginini.     

A comparison of two ELISAs for the detection of antibodies to bovine leucosis virus in bulk-milk

OBJECTIVE: To estimate the sensitivity, specificity and detection limits for two bulk-milk enzyme-linked immunosorbent assays, the Svanovir BLV-gp51-Ab and the Lactelisa BLV Ab Bi indirect tank 250, for the detection of antibody to bovine leucosis virus in milk. PROCEDURE: Milk samples from 27 cows known to have enzootic bovine leucosis (EBL) were serially diluted with milk from a herd known to be free from the disease. The dilution at which antibodies could no longer be detected by each test was determined. A total of 1959 bulk-milk samples submitted to a laboratory for the Victorian (EBL) eradication program were tested with both the Svanovir and the Lactelisa assays. A Bayesian approach was used to calculate maximum-likelihood estimates of test sensitivity and specificity. An additional 660 bulk-milk samples were tested with both the Svanovir and the Lactelisa assays. Herds that had positive results on either or both of the assays were subjected to blood or milk testing of individual cattle. RESULTS: The dilution of milk at which the Svanovir assay failed to detect enzootic bovine leucosis antibody in half of the samples was 1 in 40, whereas the comparable value for the Lactelisa was 1 in 200. Computer modeling of the operating characteristics of the Svanovir assay indicated that the sensitivity of that assay would be considerably lower than that for the Lactelisa, and the specificity was estimated to be higher. Evaluation of the assays using 660 bulk-milk samples showed that the Lactelisa assay detected four infected herds that were not detected by the Svanovir test. No false positive results were recorded for either assay. CONCLUSION: Use of the Lactelisa assay in the Victorian EBL eradication program will enhance disease detection and eradication, but may also result in an increased frequency of false positive bulk-milk test results.     

Experimental and natural infection with the enzootic leukosis virus of cattle

A trial was performed with heifers at the age of six to seven months. The animals were experimentally infected with the lymphocytes of a virus-productive donor. Infection was produced in all the nine cases, as demonstrated by means of the positive syncytial test. As indicated by the results of the trial, the antibodies to the enzootic bovine leucosis virus (BLV) were produced soon after experimental infection. A high sensitivity of the serum-neutralization test and the ELISA method was demonstrated in this connection: by these methods, the antibodies were identified already two to three weeks after experimental infection whereas by the immunodiffusion test they could be detected only after five weeks. Twenty-four animals were exposed to natural contact infection. Within 270 days of the trial, the disease after contact was recorded only in one heifer out of the four that were in close contact with the experimentally infected animals. In this case, as compared with experimental infection, the antibodies were produced much later--after 85 to 93 days. Leucosis was recorded in none of the remaining animals. The reasons why such a favourable result was obtained were the thorough disinfection of the stables after blood collections and the strict observance of the aseptic conditions. The results of experimental infection in three cows were identical with those obtained in young cattle. In the experimentally infected dairy cows, antibodies in milk were determined by the ELISA method. As found, in milk the antibodies to BLV appear two to three weeks later than they do in serum. The ELISA method of BLV antibody detection can be used for the identification of infected animals in herds where enzootic bovine leucosis occurs.     

Cost-effectiveness of bulk-tank milk testing for surveys to demonstrate freedom from infectious bovine rhinotracheitis and bovine enzootic leucosis in Switzerland

In Switzerland, annual surveys to substantiate freedom from infectious bovine rhinotracheitis (IBR) and enzootic bovine leucosis (EBL) are implemented by a random allocation of farms to the respective survey as well as blood sampling of individual animals at farm level. Contrary to many other European countries, bulk-tank milk (BTM) samples have not been used for active cattle disease surveillance for several years in Switzerland. The aim of this project was to provide a financial comparison between the current surveillance programme consisting of blood sampling only and a modified surveillance programme including BTM sampling. A financial spreadsheet model was used for cost comparison. Various surveillance scenarios were tested with different sample sizes and sampling frequencies for BTM samples. The costs could be halved without compromising the power to substantiate the freedom from IBR and EBL through the surveillance programme. Alternatively, the sensitivity could be markedly increased when keeping the costs at the actual level and doubling the sample size. The risk-based sample size of the actual programme results in a confidence of 94,18 % that the farm level prevalence is below 0,2 %. Which the doubled sample size, the confidence is 99,69 % respectively.     

The economic value of a protective vaccination against enzootic bronchopneumonia of cattle

The bovine enzootic bronchopneumonia is a multi-causal determined and by several factors triggered general factor-disease. Since therapy is mostly disappointing, prophylaxis is the most advantageous way to curb the disease. Vaccination with combined vaccines has been very promising. A cost-benefit-analysis shows that the decrease in morbidity from 72% to 7.3% and in mortality from 5.1 to 0.9% results in a benefit-cost-relation between 5 to 1 and 7 to 1. That means preventive vaccination against crowding associated enzootic bronchopneumonia saves approximately 180,- DM per animal and 250,- DM per animal in case of seasonal enzootic bronchopneumonia.     

Bovine leucosis virus contamination of a vaccine produced in vivo against bovine babesiosis and anaplasmosis

Contamination of a batch of tick fever (babesiosis and anaplasmosis) vaccine with bovine leucosis virus (BLV) was detected when a herd, in the final stages of an enzootic bovine leucosis (EBL) accreditation program, developed a large number of seropositive cattle following use of tick fever vaccine. Investigations incriminated a single calf used to produce Anaplasma centrale vaccine from which 13,959 doses were distributed. The failure of this calf to give a positive agar gel immunodiffusion (AGID) test before use was not fully explained. A total of 22,627 cattle from 111 herds receiving contaminated vaccine was tested to validate claims for compensation. Results showed infection rates of 62% and 51.8% in vaccinated dairy and beef cattle, respectively, compared with 6.1% and 1.5% in non-vaccinated cattle in the same herds. The results also indicated that infection did not spread from vaccinated to non-vaccinated in-contact cattle. Heavy reliance is now placed on purchase of calves for vaccine production from EBL accredited-free herds and on transmission tests from the calves to sheep to prevent a recurrence of contamination. The need for a BLV antigen detection test, with the sensitivity of the sheep transmission test but simpler and faster to perform, is evident.     

Enzootic bovine leukosis in New Zealand--a case report and update

Enzootic bovine leukosis was diagnosed in an 8-year-old Friesian cow which had lost condition and was milking poorly. The cow had a severe nonregenerative anaemia, panhypoproteinaemia and lymphoid leukaemia. At necropsy there was widespread lymphoid infiltration of many organs, including the abomasal mucosa, myocardium, uterus, kidney, lymph nodes and bone marrow. Antibodies against bovine leukaemia virus were detected in the serum. Although clinical enzootic bovine leukosis is rare in New Zealand, having been confirmed on only five properties, infection with the causative agent, bovine leukaemia virus, is more widespread. The results of a recently completed survey of bulk milk samples using an enzyme-linked immunosorbent assay for bovine leukaemia virus antibodies suggest that there are about 300 dairy herds in the country with a bovine leukaemia virus infection level of at least 5-10%. The economic impact of enzootic bovine leukosis on the productivity of New Zealand's dairy cattle population is probably still negligible but the introduction of control or eradication schemes in Europe and North America could sooner or later lead to restrictions on the export of live cattle and genetic material from New Zealand.     

Does control of bovine viral diarrhoea infection make economic sense?

AIM: To provide an economic analysis of the costs of control or eradication of bovine viral diarrhoea (BVD) against the estimated costs of the disease. METHODS: A decision-tree approach was adapted to an analysis of the costs of bovine viral diarrhoea virus (BVDV) infection and that of three main control options (vaccination, test-and-cull, and increased biosecurity) and their combinations, to the dairy industry in New Zealand. The model was based on an average herd of 322 milking cows. Endemic, epidemic and sporadic effects of BVDV infection were modelled in the herd, to derive an estimate of costs. RESULTS: The cost of BVDV infection to an infected average-sized dairy herd in New Zealand was estimated to be NZ $11,334 (or NZ $35.19 per cow) per annum, and NZ $48,311 over 10 years. Based on these calculations, the estimate of the annual cost of BVDV infection to the dairy industry in New Zealand was in excess of NZ $23 million per annum. While all of the control options required financial input, the rate of return compared with the cost of BVD, when viewed over a 10-year term, was as high as 123%. CONCLUSIONS: All control options offered considerable savings compared with the cost of BVD infection, and control is economically favourable. Uncertainty over the likely efficacy of the control options under field conditions in New Zealand would not allow a firm choice of one option over another at this stage, and more work on determining the efficacy of those control options in New Zealand is needed.     

Improved test for the detection of reverse transcriptase of bovine leukosis virus

The revertase test with exogenous matrix, poly-(rA) . oligo-(dT), for the detection of bovine leukemia virus from crude virus sediments was standardised and miniaturised. An amount of 10 ml of cell culture supernatant of short-term cultured lymphocytes (5 . 10(6) cells/ml) is quite sufficient for testing one cattle sample. The lower sensitivity limit of the test was found to be 10(6) virus particles. The test is properly reproducible, within tolerance limits of +/- 20--30 per cent, provided that optimum lysis conditions be maintained (0.01 per cent triton X-100, 20 minutes, 0--4 degrees C incubation) and under the condition that the protein quantity in 100 microliter test solution does not exceed the threshold of 3--15 micrograms. The specificity of the test is based on the use of free viruses from cell culture supernatant, the optimum temperature of the revertase reaction at 25 degrees C, which actually deviates from that for cellular DNA polymerases, that is 37 degrees C, and magnesium ion concentration which has to be optimum for bovine leucosis virus revertase. Two-hundred heads of cattle, differing by haematological status, were examined, and 56 per cent of them were, clearly, virus producers, among them 95 per cent of all animals with positively established leucosis and 36 per cent of the haematologically intact animals. Examinations of individuals have shown that in repetitive checks, carried out in intervals between two months and one week, the revertase activities varied by something between 0.5 and two magnitudes.     

The control of bovine leukosis in denmark, Epidemiologic and diagnostic aspects.

The Danish programme to control bovine enzootic leukosis was initiated in 1959 and intensified in 1969. The programme has resulted in a sharp decline in total and relative numbers of leukotic tumor cases in adult animals. However, total eradication of bovine leukosis has not yet been achieved, and the statistics from recent years seem to indicate that the present programme based on haematological and histological examinations will control but not eradicate the disease. An immunodiffusion test based on an internal protein (p 24) antigen has been used experimentally. This test is a valuable tool in herd diagnosis, but it is not sensitive enough for accurate single animal diagnosis.     

Classification of 1,198 cases of bovine lymphoma using the National Cancer Institute Working Formulation for human non-Hodgkin's lymphomas.

A retrospective histologic study was made of 1,198 cases of bovine lymphoma using the National Cancer Institute Working Formulation for human non-Hodgkin's lymphoma. This classification scheme was found to be readily applicable to bovine lymphoma. Most of the cell types described in the National Cancer Institute Working Formulation occurred in this series of bovine lymphomas, but the distribution of cell types varied markedly compared to that of human beings. Eighty-nine percent (1,067/1,198) of bovine lymphomas were high-grade tumors. The diffuse large cell type and its cleaved variant comprised 65.9% of all bovine lymphomas. Similar to the dog, but in marked contrast to human beings where at least 34% of non-Hodgkin's lymphomas were follicular, follicular tumors were found to be extremely rare in cattle (0.3% or 4/1,198). The prevalence of cell types varied significantly between the enzootic and sporadic lymphomas. The cleaved variant of the diffuse large cell type constituted 38% (406/1,072) of enzootic lymphomas versus 14% (18/126) of sporadic lymphomas. The mitotic index (100 x oil immersion field, 175 microns in diameter) of enzootic lymphomas (3.72 +/- 0.06, mean +/- standard error) was significantly greater than the mitotic index of sporadic lymphomas (2.82 +/- 0.17). We concluded that the cleaved variant of the diffuse large cell type with high mitotic index is characteristic of enzootic lymphoma. This characteristic high-grade cell type may be a consequence of the viral etiology of the enzootic form of bovine lymphoma.     

Control and eradication programme of enzootic bovine leucosis (EBL) from selected dairy herds in Turkey

Serum samples of 15,909 cattle from 31 dairy herds located in various regions of Turkey were tested for the presence of antibodies against bovine leucosis virus (BLV) using Agar Gel Immuno-diffusion technique (AGID). 48.3% (15/31) of the herds had seropositive animals and positivity rates were detected from 0.5-34.4% in these herds. In an EBL control/eradication programme all seropositive animals were culled in the infected herds. Thereafter, a total of 74,347 sera were tested for the presence of BLV specific antibodies. The serological results and detail of EBL control/eradication programme were shown in this paper.     

Studies of Mycoplasma mastitis in cattle. 7. Mycoplasma mastitis in 3 dairy cattle herds

Reported in this paper is the occurrence of enzootic mastitis in three dairy cattle stocks. The outbreaks had been caused by Mycoplasma bovis, Acholeplasma laidlawii, Acholeplasma axanthum as well as by one unidentified strain of the family of mycoplasmataceae. All animals with positive response to mycoplasma tests were identified an selected by repetitive testing of cultures in milk samples which had been taken from all lactating and dry cows and heifers as well as by evaluation of organ samples obtained from slaughtered cows. Regular cleaning and disinfection of stands in cowsheds, cattle tracks, and milk parlours as well as disinfection of udders and milking cups worked extremely well throughout the action in control of those cases of enzootic mycoplasma mastitis.     

Enzootic pneumonia (EP): the partial curing of EP-reinfected swine herds as an alternative to total cure

Using a partial sanitation method "Enzootic Pneumonia" (EP) could be eradicated in 17 EP-reinfected pig breeding herds. Partial sanitation includes separation measures in form of a piglet and gilt free interval on one side and as an additional protection against reinfection the temporary feeding of a medicated diet on the other side. Frequent herd controls for several years as well as mixed fattening experiments with carcass examination combined with milk and blood serology served as criteria for the sanitation success. From these results it is concluded that the infection pathway of EP is mainly maintained by young animals in the herd. Contrary to total sanitation, which will amount to at least sFr. 720 per sow, partial sanitation will only cost between sFr. 40-170 per sow, depending on herd size. Therefore, partial sanitation may be regarded as a full alternative to total sanitation after an outbreak of EP.     

Bovine leucosis (lymphosarcoma): a clinical study of 60 pathologically confirmed cases

The clinical features of 60 pathologically confirmed cases of bovine leucosis (lymphosarcoma) are described. The majority of cases could be classified into one of four distinct clinical forms, ie, juvenile multicentric, thymic, skin and adult multicentric. Diagnosis of leucosis in animals with these forms was possible on clinical grounds alone. Five animals, four of which were adult, could not be thus classified and diagnosis required haematological and, or, pathological examinations. The clinical, epidemiological and serological findings would suggest that the cases were examples of sporadic bovine leucosis.