Browsing by Subject "Johne's disease"
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Item An Environmental Perspective to Decision-making for the Control of Johne's Disease on Beef Ranches(2010-10-12) Benjamin, Lisa A.Biosecurity practices for Mycobacterium avium subsp. paratuberculosis (Mptb), the etiologic agent for Johne's disease (JD), are predicated on the fact that fecal-oral is the major route of infection and that Mptb is present in the environment of affected farms. The objectives of these studies were to describe perceived benefits of testnegative Level 4 status in the Voluntary Bovine Johne's Disease Control Program (VBJDCP), describe producer and veterinarian attitudes towards JD relevant biosecurity practices, compare 5 JD control options using a Markov model, determine if tangential flow filtration (TFF) increases the detection sensitivity for Mptb and describe the distribution of environmental predictors for Mptb survival. Twenty-five percent and 39% of beef producers in the VBJDCP reported that they received substantial or marginal benefits (financial and non-financial), respectively, from program participation. Producers suggested increased marketing opportunities to improve the VBJDCP. Producers in a cross-sectional mailed survey of attitudes towards biosecurity practices were more likely than veterinarians to agree that separating JD clinical or suspects from calves or heifers; acquiring replacements or additions from JD low-risk herds, testing for JD every 10 to 14 months and test and culling clinical suspects only were useful for control of JD. A state transition Markov model, with the environment as the source of Mptb, was used to compare 6 alternative control strategies for JD. Management and the probability of Mptb surviving 1 year in the environment were important determinants of the prevalence of subclinical JD on beef farms under the analyzed control strategies. Heterogenous distribution of environmental predictors for Mptb survival was observed in spatial risk maps. In conclusion, although some beef producers experienced gains from participation in the VBJDCP, the perceived program benefits could be improved by increased marketing and education on the advantages of participation. Specific problem areas should be addressed. The length of time Mptb survived in the environment was an important parameter in the Markov chain model. Additionally, due to the heterogenous distribution of environmental predictors, a multiscale approach to sampling and analysis should be useful.Item Effects of seasonal heat stress on the diagnosis of Mycobacterium avium subsp. paratuberculosis in Texas dairy cattle(Texas A&M University, 2005-11-01) Strickland, Summer J.The validity of Johne??s disease herd status programs and on-farm disease control programs that rely on established ??cutpoints?? (e.g., S/P ratios) for ELISA serological tests such as the HerdChek?? (IDEXX Laboratories Inc., Westbrook, Maine) may be susceptible to varied seasonal test accuracy. An observed depression in the proportion of a large central Texas dairy herd classified as ??positive?? during the months of July and August led to our investigation. We hypothesized that there exists a seasonal variability in serological response to Mycobacterium avium subsp. paratuberculosis that is directly related to heat stress. We further hypothesized that a reciprocal response may occur during periods of heat stress that results in a greater risk of fecal shedding in subclinically-infected animals. Starting in October 2002, we invoked a testing regime that included multiple testing of 720 individual adult cows over each of four seasons including spring, summer, fall, and winter. We collected serum on a cyclic, monthly basis from three random groupings of cows, and, based on the ELISA results, collected fecal samples from the 20% of cows with the highest S/P ratios. We continued to sample in this manner for the period of one year and at the end of that period, analyzed the serum en masse. The ELISA outcome values were treated both as categorical and continuous variables (e.g., S/P ratio). The potential lagged effects of heat stress on S/P ratio, as well as the potential for a change in test result (negative to positive or vice versa) due to heat stress were assessed. The results for fecal culture were analyzed on a categorical scale and were compared to the ELISA results to explore the possibility of a reciprocal response. In the present study, we did not observe any of the significant seasonal effects of heat stress on S/P ratios and proportion seropositive to MAP that were observed in the historical (and less valid) cross-sectional time-series data conducted in 2001. In addition, we found no evidence to support a hypothesis linking seasonal heat stress to the risk of fecal culture positivity for the causative bacterium for Johne??s disease.Item Genetic analysis of mycobacterium avium subspecies paratuberculosis reveals sequence and epigenetic variation among field isolates(2009-05-15) O'Shea, Brian JamesPrevious research performed in 1999 by Harris et al. has shown that many varieties of ruminants serve as the host species for Mycobacterium avium subspecies paratuberculosis (MparaTb) infections. Gene sequencing has supported the contention that organisms isolated from different hosts harbor different gene sequences; this has been exemplified by Amonsin et al. in 2004 with the sequencing of the mfd (transcription-repair coupling factor) and by Motiwala et al. in 2005 through sequence analysis of phosphatidylethanolaminebinding proteins which reveal a host-specific correlation of isolates. Some contradicting reports from Bannantine et al. from 2003 have further claimed that MparaTb is a monogenic organism based upon sequence data from regions flanking the origin of replication and the 16s rRNA. One of the drawbacks to the techniques implemented in these reports is the extremely restricted region of the bacterial genome that was analyzed; furthermore, only a select number of isolates were analyzed. In the present studies, amplified fragment length polymorphism (AFLP) was used as a tool for a genome scale comparison of MparaTb isolates from differing isolation types as well as a comparison of MparaTb isolates to the genetically similar yet avirulent Mycobacterium avium subspecies avium isolates. AFLP data reveals the MparaTb genome to be much more plastic and polymorphic than previously thought. These polymorphic regions were identified and characterized and are shown to be unique to the organism when compared to an array of Mycobacterial isolates of differing species. These polymorphic regions were also utilized in polymerase chain reaction (PCR) based diagnostic as well as epidemiologic tests. Furthermore, AFLP comparative analysis of intracellular and fecal MparaTb isolates reveals polymorphic regions unique to each isolate type. While these genomic differences are not based upon differences in the genetic code, they are based upon epigenetic modifications such as DNA methylation. These DNA methylation patterns are unique to intracellular MparaTb isolates as opposed to isolates from fecal material. Furthermore, AFLP comparisons of fecal MparaTb isolates that were passaged through the bovine ileum revealed banding pattern differences as compared to the original inoculum.