Download or read book Study of Prevalence Risk Factors and Lifetime Impacts of Infection with Bovine Leukemia Virus in the Canadian Dairy Industry written by Omid A. Nekouei and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The overall goal of the research described in this thesis was to lay a proper foundation for designing and conducting efficient control and eradication programs for infection with bovine leukemia virus (BLV) in the Canadian dairy industry. The objective in Chapter 2 was to identify potentially important risk factors for BLV infection in Canadian dairy herds. Of 272 study herds, from 8 provinces of Canada and tested during 1998-2003, 78% were BLV-positive. Over 15 management determinants for the infection were evaluated. Herds with clinical cases of leukosis during the 12 months prior to sampling, as well as herds which purchased animals with unknown BLV infection status in the last five years, had a significantly increased proportion of BLV-positive cows. Herds from eastern provinces and those not purchasing cows in the last five years were more likely to be free from BLV compared to western provinces and farms purchasing cows in the last five years. The objective in Chapter 3 was to determine the lifetime effects of BLV infection on milk production and longevity of dairy cows in Canada. Overall, 4052 cows from 348 herds were enrolled in a historical cohort study, based on test results from 1998-2003 and lactation and culling records post-testing until 2013. Positive cows to BLV had consistently greater probability of being culled (or dying) than the negative cows (over lifetime lactations 2-7). Only BLV-positive cows with short longevity (2 and 3 lifetime lactations) had a significantly lower lifetime milk production compared with their negative counterparts. As the cows lived longer (> 3 lactations), the difference in milk production between the two cohorts was no longer significant. The objectives of Chapter 4 were: 1) to assess the potential for carryover of antibodies against BLV in milk samples obtained from shared meters; and 2) to determine if adjustment of the diagnostic test cut-off value would improve the test characteristics for meter-collected milk ELISA results. The study included 236 paired milk samples from 8 dairy farms in Prince Edward Island collected in 2013. Two simultaneous milk samples, one hand-collected at the beginning of milking, and the other from the corresponding milk meter, were taken from all lactating cows that were milked at the selected meters. The sequence of cows using each meter was recorded. Carryover of BLV antibodies at shared milk meters was significant. For low-titer cows, the carryover effect was positively associated with the titer of the preceding cows. This could result in generating false-positive results in the BLV antibody-ELISA test on meter-collected samples from dairy herd improvement (DHI) procedures. Based on a new optimal cut-point, a suspicious category on the ELISA titers was defined, and a retest on the samples falling within this range was recommended to reduce the false positive rate. The objectives for Chapter 5 were: 1) to determine the prevalence of BLV infection at the herd level using a bulk-tank milk (BTM) antibody ELISA in the Maritime region of Canada ; and 2) to develop applied statistical models for predicting within-herd prevalence of BLV infection using the BTM antibody levels. To detect BLV infection and the antibody levels, a census was implemented on BTM samples from all dairy farms in the Maritime region in 2013 (3 monthly rounds of sampling on 623 farms). Another round of BTM sampling was coincided with individual cow sampling (all cows that contributed milk to the fourth BTM) in 90 selected herds. Herd-level prevalence of BLV in the Maritime region was 90.8%. In the individual testing, 30.4% of cows were positive. The statistical models developed in this study were able to predict true within-herd prevalence of BLV reasonably well based only on the BTM results. The model including all BTM tests (4 rounds of sampling) as the predictor had the best fit, although the models using 2 and 3 BTM tests provided similar results to 4 repeated tests. The focus for Chapter 6 was to assess the diagnostic performance of a commercially available ELISA for detecting BLV antibodies in BTM samples collected from dairy herds in Eastern Canada in 2013. Of 133 tested herds, 108 herds were found to be truly infected. At the resulting optimal cut-point, sensitivity and specificity of the BTM ELISA were estimated at 0.972 (0.921 - 0.994) and 1 (0.863 - 1), respectively. With the high prevalence of BLV infection across Canada and its detrimental economic impacts, pursuing broad-based control programs is necessary. All of the findings in the present research could contribute to designing and conducting efficient BLV control programs.

Download or read book Field Studies on the Control of Bovine Leukemia Virus in Dairy Cows written by Vickie J. Ruggiero and published by . This book was released on 2019 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt: Bovine leukemia virus (BLV) is an oncogenic deltaretrovirus of cattle that is estimated to infect more than 40% of U.S. dairy cows and cost the dairy industry hundreds of millions of dollars per year. BLV inserts a DNA copy (provirus) into the host genome and can cause leukemia and lymphoma in 1-5% of infected animals, while around 30% develop a non-malignant lymphocytosis, often coupled with high proviral load. BLV infection in dairy cows has also been associated with a number of economically important effects, such as decreased milk production, longevity, and immune function. The primary goal of this dissertation was to develop management protocols that can be implemented on U.S. dairy operations. We also aimed to further characterize in vivo immunologic effects of BLV infection, especially at mucosal junctions, hypothesizing that BLV+ cows would have lower concentrations of IgA antibody. To test the effect of BLV infection on total IgA concentrations, we analyzed the milk, saliva, and serum of BLV+ cows with varying lymphocyte count and proviral load profiles for comparison with BLV- herd mates. We found that BLV+ cows exhibited numerically lower concentrations of IgA in both milk and saliva, but not serum, in comparison to BLV- cows. Although the observed decreases were not statistically significant, the biological effects remain unknown. We also observed that the lowest concentrations of IgA were seen in the milk and saliva of BLV+ cows without lymphocytosis or high PVL, and these differences were trending toward significance. Our data, if confirmed, suggests that BLV may be disruptive to the immunology of mucosal junctions. We developed and implemented three field trials to evaluate management protocols for control of BLV in dairy herds. The first trial investigated the frequently suggested management intervention of improved medical hygiene by changing from shared needles and reproductive sleeves to single-use items. In this field trial, BLV- herd mates were assigned to control (re-use) or intervention (single-use) groups and the incidence risk was calculated semi-annually. Although we saw no difference in the risk of new infections in our study, medical hygiene may still play a role in the transmission of BLV as well as other diseases. This study also identified an increase in incidence risk in the summer exposure period. Meanwhile, our second field trial was a novel intervention which used milk ELISA screening to identify BLV+ cows for further characterization of their lymphocyte count (LC) and proviral load (PVL). In this manner, we identified cows thought to be the most infectious to their susceptible herd mates, and worked with herd managers to create a priority removal plan to consider when culling cows or implementing segregation measures. Overall, the three enrolled herds significantly reduced both BLV prevalence and incidence risk over a 2 to 2.5 year period. In this study, no significant associations with season were observed. Our final field trial aimed to demonstrate that milk ELISA testing could be used in herds with low BLV prevalence in order to identify and remove the few remaining BLV+ animals and achieve eradication of the virus. Two herds that were able to remove all BLV+ adult cows were generally successful, though the young stock (first lactation heifers) were a reservoir for reintroduction. In addition, we observed 5 first lactation heifers in one herd which had previously tested negative on serum ELISA but later tested positive on milk ELISA after entering the milking herd. This agrees with reports of latent BLV infections, and provides further evidence that long-term surveillance and further research on the infection dynamics of BLV are needed.

Download or read book A Baseline Study to Determine the Prevalence of Infection with Bovine Leukemia Virus in Dairy Cows on Prince Edward Island written by Canada. Agriculture Canada and published by [Charlottetown, P.E.I.] : Agriculture Canada. This book was released on 1990 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Bovine Leukemia Virus in Beef Cattle written by Oscar Javier Benitez Rojas and published by . This book was released on 2019 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt: The chronic lymphoproliferative disorder, bovine leukosis, is caused by the deltaretrovirus bovine leukemia virus (BLV). Surveys indicate that 39% of the US beef cow-calf operations have at least one BLV-infected animal compared with 83% of dairy herds. Most BLV infected cattle remain asymptomatic and act as carriers of the virus while less than 5% progress to lymphosarcoma. There are limited studies on the impact of BLV in beef cattle. Understanding the impact as well as identifying important route of disease transmission in beef cattle enterprises is important to better design intervention strategies. The primary goals of the studies described in this this dissertation were to 1) further understand the risk of breeding bulls in the transmission of BLV and 2) to determine the effect of BLV on the survival of cattle in beef and dairy herds. We first determined BLV prevalence in breeding beef bulls and the presence of BLV provirus DNA in genital secretions (smegma and semen). In our study population, 44.6% of beef bulls were seropositive for BLV and 48.7% of herds had at least 1 BLV-infected bull. Bovine leukemia virus provirus DNA was detected in smegma samples of 4/54 (7.4%) BLV-seropositive bulls and represent a potential risk for the transmission of BLV from infected bulls to uninfected cows during natural service breeding programs. To evaluate this risk, we exposed BLV negative heifers to a BLV positive bull during a defined 38-day breeding period. Although BLV provirus was found in the smegma and blood of the BLV positive bull prior to and after the breeding period, we detected no evidence of seroconversion or presence of BLV provirus DNA in the blood of naive heifers. These results suggest that BLV infected bulls that are healthy and aleukemic may not be a significant risk of BLV transmission during a defined breeding season.We next evaluated the impact of BLV infection on beef and dairy cow' longevity within herds. The presence of BLV antibodies in blood was not associated with a change in beef cow longevity over 2 years monitoring period, but decreased survival was observed in cattle in which BLV infection had advanced clinically as indicated by a high BLV provirusload in blood. In dairy cows, we demonstrated that infected females lived significantly shorter than their negative herd mates and were at a 30% greater hazard of being culled compared with BLV negative cows. In summary, there is high prevalence of BLV in breeding beef bulls which could serve as a source of transmission both within and between herds. Based on our study results, the risk of transmission of BLV from healthy infected bulls to naive heifers is low when bulls are housed with heifers for a defined breeding period, but this scenario should not be considered without risk. BLV does not appear to have an impact on beef cow longevity, but in contrast, is associated with decreased longevity in dairy cows. These studies provide important information for supporting and designing risk based BLV control programs.

Download or read book Dynamics of Bovine Leukemia Virus Transmission on a California Dairy written by Marie-Liesse Lassauzet and published by . This book was released on 1988 with total page 386 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Surveillance and Control of Enzootic Bovine Leucosis in Atlantic Canada written by Emily Elizabeth John and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This research included four studies investigating bovine leukemia virus (BLV) in Atlantic Canada (New Brunswick, Newfoundland and Labrador, Nova Scotia, and Prince Edward Island). The current herd-level prevalence of BLV in dairy herds in Atlantic Canada was determined in the first study. The within-herd prevalence was estimated based on testing bulk tank milk for anti-BLV antibody levels. A risk assessment and management program workbook was designed and implemented using a subset of dairy herds in Atlantic Canada to investigate management factors associated with the BLV estimated within-herd prevalence. Herd-level prevalence for BLV was high with at least 88% of dairy herds in Atlantic Canada containing at least one BLV-seropositive cow. Farms with a history of diagnosing clinical disease associated with BLV infection, as well as farms where calves received colostrum from cows of unknown BLV status, were more likely to have an estimated within-herd BLV prevalence of at least 25% compared to herds without a history of clinical disease or herds where calves did not receive colostrum from BLV-unknown or BLV-infected cows. The second study investigated the variability between bulk tank milk samples from the same herd collected over different sampling intervals, as well as the variability between samples collected from different farms. Farms in the Canadian Maritimes (New Brunswick, Nova Scotia, and Prince Edward Island) participated. Samples from 2013 were collected at 1-month intervals and those from 2016 were collected at 3-month intervals. Samples were analyzed for the presence of anti-BLV antibodies and estimated within-herd prevalence was calculated for each herd. The most variability was seen in samples collected from different herds, and the least variability was seen in samples from the same herd collected at 3-month intervals. This information can help in designing sample collection intervals for disease monitoring or control programs. The third study investigated the age group of calves, heifers, and adult cows in which BLV was first identified. Most previous research has focused on adult cows, but calves and heifers are also able to become infected with BLV prior to entering the milking herd. Blood samples were collected from 6 pre-weaned calves, 6 weaned heifers, and 6 breeding-age heifers on 56 dairy farms in Atlantic Canada, and a questionnaire was administered to farmers asking about age-specific management factors for these three age groups as well as for adult cows. The majority of farms had BLV first identified in either the adult milking herd or in pre-weaned calves. Management factors associated with the age group where BLV was first identified included the number of times weaned heifers were regrouped after weaning, the type of fly control used in breeding-age heifers, the use of foot-trimming implements in breeding-age heifers, and whether the farm purchased bred heifers. The final study investigated the utility of commonly available, cost-effective diagnostic tests to predict proviral load (PVL) in BLV-seropositive cows. It is suspected that cows with a higher PVL are a higher infection risk to naïve cows than those with a low PVL. Currently there is no commercial test for PVL in cows, and so blood and milk were collected from 339 BLV-seropositive cows as well as basic demographic information. PVL was determined using qPCR, and blood was also used for determining anti-BLV antibody levels and for performing complete blood counts. Milk samples were analyzed for standard components by the regional dairy herd improvement agency, as well as having anti-BLV antibodies measured. The milk antibody level, as well as blood lymphocyte count, were significantly associated with increasing PVL.

Download or read book Transmission and Progression of Bovine Leukemia Virus written by Holden Chase Hutchinson and published by . This book was released on 2020 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt: Bovine leukemia virus (BLV) is a deltaretrovirus which infects more than 40% of the United States cattle population and more than 85% of U.S dairy herds. Upon infection of a susceptible host, BLV reverse transcribes its viral RNA genome into a DNA provirus that integrates into the cellular DNA of the host, resulting in a lifelong infection. Clinical outcomes of BLV infection are the development of lymphocytosis in more than 30% of infected cattle and the development of lymphoma in less than 10%. Furthermore, BLV infected cattle have been shown to be immunocompromised, to produce less milk, and to have shortened lifespans when compared to their uninfected herd mates. Collectively, these impacts warrant the consideration of disease eradication from the U.S. cattle population. In fact, eradication has already been achieved in more than 21 countries, predominately within the European Union.One objective of our BLV research team has been to develop BLV management solutions that are both practical and economically feasible. The goal of this dissertation was to contribute to these efforts by providing a greater understanding of the routes through which BLV can be transmitted, by describing how BLV progresses over time to disease states associated with increased infection potential, and by understanding how newly available diagnostics can best be utilized to detect BLV infections.To contribute to the identification of BLV transmission routes, a statistical model was built to examine the association between herd management practices and the BLV incidence rate among Michigan dairy herds. This analysis estimated the marginal incidence rate in Michigan dairy herds to be 2.11 infections per 100 cow-months at risk. Herd management practices positively associated with herd-level rate of infection were herd prevalence, the frequency of needle reuse, housing post-parturient cows separately, and increased milking frequency. The use of sand bedding appeared to have protective effects and was negatively associated with the incidence rate. To describe how BLV progresses over time, longitudinal observations on proviral load, lymphocyte counts, and ELISA test results collected during an intervention field trial were analyzed. The results from this analysis indicated that negligible increases in lymphocytes and small increases of approximately 3,000 proviral copies per 100,000 cells occurred over a six-month interval. Additionally, infected cattle with low proviral loads and normal lymphocyte counts were the most likely to experience changes in ELISA status that may result in ELISA false-negatives. To determine our ability to detect BLV infections and to examine the role early infection plays in long-term disease progression, fifteen steers were experimentally infected with BLV and followed for 147 days. This study found that new infections are detected by PCR on average 24 days post infection prior to detection by ELISA at 36 days post infection. Furthermore, the observations on early viral kinetics suggest BLV proviral load and lymphocyte count levels may be established soon after initial infection. Overall, the results of this dissertation contribute to ongoing BLV control efforts by identifying new potential routes of transmission that can be explored in future intervention trials, finding that the development of PVL and LC may not be the result of gradual disease progression but may be established shortly after infection, and determining the relationships among the various BLV diagnostic tests.

Download or read book Bovine Leukemia Virus Zoonosis written by Kenneth Nathaniel Loyd and published by . This book was released on 2019 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this study is to test for the presence of bovine leukemia virus (BLV) in both pasteurized and unpasteurized dairy milk samples. During the course of the thesis, steps will be taken to identify the prevalence of this virus in dairy milk. Studies have shown that BLV DNA has been found in humans, with particles/DNA (depending on what found) in the secretory mammary epithelium within secretory mammary epithelium. However, the correlation of viral particle presence to BLV infection and prevalence in dairy milk is not completely understood. The overall goal of this thesis is to determine mode of BLV transmission through bovine dairy consumption.

Download or read book An Introduction to Survival Analysis Using Stata Second Edition written by Mario Cleves and published by Stata Press. This book was released on 2008-05-15 with total page 398 pages. Available in PDF, EPUB and Kindle. Book excerpt: "[This book] provides new researchers with the foundation for understanding the various approaches for analyzing time-to-event data. This book serves not only as a tutorial for those wishing to learn survival analysis but as a ... reference for experienced researchers ..."--Book jacket.

Download or read book Toxicological Profile for Chlordane written by and published by . This book was released on 1994 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Human Retrovirology written by William A. Blattner and published by Raven Press (ID). This book was released on 1990 with total page 520 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Bibliography of Agriculture written by and published by . This book was released on 1992 with total page 1742 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Tolerable upper intake levels for vitamins and minerals written by European Commission. Scientific Committee on Food and published by . This book was released on 2006 with total page 478 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Zoonoses and Communicable Diseases Common to Man and Animals Bacterioses and mycoses written by Pedro N. Acha and published by Pan American Health Organization. This book was released on 2001 with total page 406 pages. Available in PDF, EPUB and Kindle. Book excerpt: In recent years, zoonoses and communicablediseases common to man and animals have gained increasing attention worldwide.Human diseases that have their origins in infected animals--such as AIDS, SARS, andCreutzfeldt-Jakob--have highlighted the need for a better understanding ofanimal diseases. The ease and speed of modern travel facilitatesthe spread of diseases once confined to specific geographic areas, as recentlyoccurred with the Covid-19 epidemic. Animal migration and trade pose a similarthreat, as was shown by the outbreaks in the United States of West Nile feverand monkeypox--two diseases not previously known in the Western Hemisphere. Eachof these examples highlights the need for accurate, up-to-date information, such as that presented here in the latest edition of Zoonoses and Communicable Diseases Common to Man and Animals. This edition, published for the first time inthree volumes, covers: I.Bacterioses and mycoses II.Chlamydioses, rickettsioses, and viroses III.Parasitoses The books provide a detailed overview of themost important historic and emerging zoonotic diseases, such as Ebolahemorrhagic fever, foot-and-mouth disease, influenza, giardiasis, Japaneseencephalitis, shigellosis, and spongiform encephalopathies, with informationranging from their first appearance and most important outbreaks to the latestscientific knowledge of the diseases and their causative agents. The chaptersprovide the following key information on each disease: etiology geographicdistribution symptoms and occurrence in man and animals source of infection andmode of transmission role of animals in its epidemiology diagnostic techniques, and prevention and control measures Numerous tables and figures diagrammingmodes of transmission complement the text. The book is an essential tool for biologists, parasitologists, virologists, veterinarians, doctors, epidemiologists, andworkers in public health and animal health institutions, as well as forteachers, researchers, and students in these fields. All of them will find valuablematerial to enrich their collection of reference works in the third edition ofZoonoses and communicable diseases common to man and animals. Volumes 2(Chlamydioses, rickettsioses, and viroses) and 3(Parasitoses) are also available.

Download or read book Veterinary Epidemiology written by Michael Thrusfield and published by John Wiley & Sons. This book was released on 2013-04-24 with total page 1046 pages. Available in PDF, EPUB and Kindle. Book excerpt: This successful book, now in its third edition, continues to provide a comprehensive introduction to the role of epidemiology in veterinary medicine. Since the publication of the second edition there has been considerable expansion in the application of veterinary epidemiology: more quantitative methods are available, challenges such as the epidemic of foot-and-mouth disease in Europe in 2001 have required epidemiological investigation, and epidemiological analyses have taken on further importance with the emergence of evidence-based veterinary medicine. In this edition: Completely revised and expanded chapters; Increased attention given to the principles and concepts of epidemiology, surveillance, and diagnostic-test validation and performance; Many examples are drawn from both large and small animal medicine, and from the developing as well as the developed world This paperback edition includes a new section on risk analysis. Veterinary Epidemiology is an invaluable reference source for veterinary general practitioners, government veterinarians, agricultural economists and members of other disciplines interested in animal disease. It will also be essential reading for undergraduate and intermediate-level postgraduate students of epidemiology.

Download or read book Toxicological Profile for Trichloroethylene written by and published by . This book was released on 1997 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Epidemiologic Basis of Tuberculosis Control written by Hans L. Rieder and published by . This book was released on 1999 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: