Strategies for Mycoplasma hyopneumoniae control, diagnostics, and surveillance

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Silva, Ana Paula
Major Professor
Clavijo, Maria
Zimmerman, Jeffrey J
Arruda, Bailey
Wang, Chong
Giménez-Lirola, Luis
Committee Member
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Veterinary Diagnostic and Production Animal Medicine
Mycoplasma hyopneumoniae (MHP) remains one of the most challenging pathogens in the swine industry. MHP infections burden swine populations through decreased efficiency in feed conversion, increased mortality, and increased use of antimicrobials. The beneficial effects of eliminating MHP from pig farms have intensified the search for effective control strategies and diagnostic tools. The general objective of this dissertation was to evaluate MHP control strategies and the application of different diagnostic procedures to MHP surveillance in pig populations. Gilt acclimation is the core of MHP control and prevention. The goal of gilt acclimation for MHP is to lessen shedding and create a robust sow immunity to then reduce the number of positive piglets at weaning, which is a predictor of MHP-associated disease in growing pigs. Thus, several field practitioners have exposed gilts to farm-based lung homogenate contaminated with MHP using intratracheal inoculations and aerosol exposure. In Chapter Two, three routes of MHP exposure, e.g., intratracheal, intranasal, and aerosol, were evaluated in terms of detection of antibody and DNA and impact on clinical signs under controlled conditions. All routes of exposure succeeded in reproducing disease-associated MHP, e.g., positive results in antibody and DNA detection along with clinical signs and lesions. Additionally, it was shown that aerosol exposure resulted in significantly later antibody response but had a lesser impact on average daily weight gain than intratracheal exposure. Diagnostic testing is an important component of agent monitoring and surveillance. Serum antibody by ELISA remains one of the most used tests to survey non-vaccinated, MHP-negative populations. Thus, it is critical to understand diagnostic performance of commercially available MHP serum ELISAs. In Chapter Three, the performance of six commercial ELISAs was evaluated under controlled and field conditions. Under controlled conditions, it was shown that three of six ELISAs resulted in no false positives and no cross-reactions with other mycoplasmas. When repeated under field conditions, these best performing ELISAs resulted in similar diagnostic sensitivity and specificity. Coughing is the predominant clinical sign of MHP-associated disease and can be used as a trigger for further investigation using diagnostic testing. In Chapter Four, the association between cough and MHP DNA detection in clinical and environmental specimens was evaluated under controlled conditions. The probability of detecting MHP DNA in pen-based oral fluids and drinker wipes increased as the frequency of coughing pigs in the pen increased. Pen-based oral fluids are a population-based sampling widely implemented in agent surveillance in the swine industry. Still, the effectiveness of oral fluid samples relies on the diagnostic capability of PCR tests. In Chapter Five, combinations of two nucleic acid extractions and three MHP PCRs were compared in terms of the probability of detecting DNA in pen-based oral fluid samples as a function of within-pen MHP prevalence. For all protocols, the probability of detection increased as within-pen MHP prevalence increased but one of the four protocols provided the highest probability of detection of MHP in pen-based oral fluids. Additionally, no false positive results were observed with any of the four protocols. In conclusion, the results from this dissertation highlight the necessity to consider the MHP biology and epidemiology when accurately selecting diagnostic testing. Further, intentional exposure to MHP can be an important tool in pathogen elimination and prevention.