Thèses (M.Sc.)--Université de Sherbrooke (Canada), 2000. / Titre de l'écran-titre (visionné le 20 juin 2006). Publié aussi en version papier.

Johne’s disease is a chronic and debilitating disease of cattle caused by infection with Mycobacterium avium subsp. paratuberculosis (Mptb). This disease affects both dairy and beef cattle, though it is more commonly recognized in dairy cattle. Mptb is able to persist in the environment of cattle for extended periods of time; therefore the distribution of the disease depends on the presence of infected animals and environmental conditions. Three surveillance systems were used to describe the spatial distribution of Johne’s disease seropositivity in Texas cattle. These three systems were hypothesized to describe different spatial patterns. These systems involved sampling, 1) herds throughout Texas, 2) market cattle from four markets each month (one each from northern, southern, eastern, and western regions of Texas) and 3) sick animals submitted by veterinarians throughout Texas. Samples were tested for Johne’s disease at the Texas Veterinary Medical Diagnostic Laboratory using serum ELISA. Spatial distributions were estimated by kriging the sample-to-positive control ratios (S/P). Sera were evaluated for Mptb antibodies from 2358 cattle with 1084 animals in system 1, 1200 from system 2 and 74 from system 3. Total number of positive ELISA results was 51, with 25, 19 and 7 positve ELISA results for systems one, two and three, respectively. Results showed an overall prevalence of 2.16%, and prevalence’s of 2.31%, 1.58% and 9.46% for systems one, two and three, respectively. Differences in the spatial distribution of Johne’s disease seropositvity, based on the three surveillance systems, confirmed our hypothesis that estimation of disease distribution is dependant upon the source of surveillance samples.

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A novel approach to control Boophilus microplus is to disrupt the physiological function of an endogenous myokinin receptor of this tick that was previously cloned in our laboratory. To test the hypothesis that this myokinin receptor might be a suitable target for development of a novel acaricide, this target was validated by immunological disruption. A mixture of peptides, corresponding to the sequence of the extracellular loops of this receptor which were synthesized and linked to a carrier protein, was injected into Hereford cattle to induce an immunological response. Immunological tests (ELISA) were developed to test the sera of these animals for antibody titers. The data were analyzed using a randomized block split plot design and were compared between the control (calves numbers 407, 408, 427, 436, and 438) and peptide-injected calves (calves numbers 417, 420, 421, 426, and 435). A gradual increase of antibody production was observed with the peptide-injected calves with bleed 4 showing the highest absorbances. Control calves and peptide-injected calves with high antibody titers were challenged with approximately 20,000 tick larvae at the USDA Cattle Tick Research laboratory. The tick challenge test determined that disruption of the receptor function produces a detrimental effect on tick physiology (development, feeding and reproduction) by looking at percentage of molting, time of survivorship, number of ticks dropped, weight of fed females, weight of egg masses, and blood meal conversion. The results, which were analyzed by a contingency table and a 2 sample T-test, did not support the hypothesis that the sera ingested from the peptide-injected cattle would cause a detrimental effect on tick physiology. There was no statistical significance in the percentage of metanymphs molting from peptide-injected calves versus control calves (p = 0.282) and in the time of adult survivorship. A statistical inference could be made about the number of ticks that dropped since four calves died of bovine babesiosis after the metanymphal collection. There was no statistical significance in the weight of fed females (p = 0.061), weight of egg masses (p = 0.885), and bloodmeal conversion (p = 0.312) from peptide-injected calves versus control calves.

A novel approach to control Boophilus microplus is to disrupt the physiological function of an endogenous myokinin receptor of this tick that was previously cloned in our laboratory. To test the hypothesis that this myokinin receptor might be a suitable target for development of a novel acaricide, this target was validated by immunological disruption. A mixture of peptides, corresponding to the sequence of the extracellular loops of this receptor which were synthesized and linked to a carrier protein, was injected into Hereford cattle to induce an immunological response. Immunological tests (ELISA) were developed to test the sera of these animals for antibody titers. The data were analyzed using a randomized block split plot design and were compared between the control (calves numbers 407, 408, 427, 436, and 438) and peptide-injected calves (calves numbers 417, 420, 421, 426, and 435). A gradual increase of antibody production was observed with the peptide-injected calves with bleed 4 showing the highest absorbances. Control calves and peptide-injected calves with high antibody titers were challenged with approximately 20,000 tick larvae at the USDA Cattle Tick Research laboratory. The tick challenge test determined that disruption of the receptor function produces a detrimental effect on tick physiology (development, feeding and reproduction) by looking at percentage of molting, time of survivorship, number of ticks dropped, weight of fed females, weight of egg masses, and blood meal conversion. The results, which were analyzed by a contingency table and a 2 sample T-test, did not support the hypothesis that the sera ingested from the peptide-injected cattle would cause a detrimental effect on tick physiology. There was no statistical significance in the percentage of metanymphs molting from peptide-injected calves versus control calves (p = 0.282) and in the time of adult survivorship. A statistical inference could be made about the number of ticks that dropped since four calves died of bovine babesiosis after the metanymphal collection. There was no statistical significance in the weight of fed females (p = 0.061), weight of egg masses (p = 0.885), and bloodmeal conversion (p = 0.312) from peptide-injected calves versus control calves.

The first objective of this study was to evaluate the utility of bulk tank tests to detect the presence of Mycobacterium avium subspecies paratuberculosis (MAP) antibody in dairy herds for the purpose of Johne’s disease surveillance. Individual cow milk samples were collected by CanWest Dairy Herd Improvement customer service representatives in herds across Ontario, Canada. These samples, along with bronopol preserved bulk tank samples were collected from herds participating in the Ontario Johne’s Education and Management Assistance Program (OJEMAP), a producer funded Johne’s control scheme. Overall, there were 309 farms tested, with herd size from 15 to 986 milking cows. The relative sensitivity and specificity of the bulk tank ELISA test when a positive herd was defined as 1 or more positive cows was 54.7% and 90.6%, respectively. The second objective was to determine the effect of milk storage temperature and duration on the Johne’s milk ELISA test result. When herd level factors were considered in a logistic model, average monthly protein (%) and the percent of positive milk contributed to the bulk tank by milk ELISA positive cows were found to be significantly (p<0.05) associated with the probability of a herd testing positive on the bulk tank Hyper ELISA protocol. Positive and negative MAP milk samples were stored for varying times and under different temperature conditions. In a mixed linear model, time was found to be significantly (<0.001) associated with the log transformed ELISA optical density. When the results were dichotomized into positive and negative by the cut-off of 0.10 and cross classified, the amount of misclassification was considered biologically negligible.

Thèses (M.Sc.)--Université de Sherbrooke (Canada), 2000. / Titre de l'écran-titre (visionné le 20 juin 2006). Publié aussi en version papier.