Swine Health and Production
Reviewer: Eileen L. Thacker
Mycoplasma hyopneumoniae continues to cause significant economic losses to the swine industry in spite of modern herd management strategies. Diagnosis and determination of time of infection caused by M. hyopneumoniae-induced respiratory disease remains problematic for veterinarians and producers. It is anticipated that new diagnostic techniques including the polymerase chain reaction and improved serological assays will aid in our ability to strategically time therapy and intervention strategies. Studies such as this need to be done to begin correlating the two assays to determine their potential uses for diagnostics as well as increasing our understanding of their strengths and weaknesses. This paper describes a study in which samples consisting of serum and nasal swabs were collected from pigs from five farms with varying M. hyopneumoniae disease problems. Profiles of seroconversions and detection of M. hyopneumoniae DNA by PCR were developed for each farm. This study found that M. hyopneumoniae DNA was detected by PCR earlier than serology. Utilizing farms with varying management styles and differing disease status demonstrated the temporal variation between that seroconversion and the presence of M. hyopneumoniae DNA. Sampling was begun when the pigs were approximately 5 weeks of age, at which time it would be anticipated that most pigs would be seronegative. At 5 weeks of age, between 10 and 50% of the pigs of the various farms had M. hyopneumoniae DNA as detected by the PCR assay. These levels increased to between 50 and 100% by time of slaughter.
It is well known that seroconversion to M. hyopneumoniae is slow process, usually taking a minimum of 4 weeks for antibodies to be detected by the Tween 20 ELISA used in this study. With the development of PCR assays to detect M. hyopneumoniae, our ability to evaluate the pattern of transmission is increased. However, while the use of a PCR assay to detect mycoplasmal DNA has advantages over serology, understanding of potential short-comings and expense needs to be considered. Due to the high sensitivity of the assay, false positive results can be a frequent concern. Research by Stark et al. (1998), detected M. hyopneumoniae in the environment and air.1 Thus, care must be taken when obtaining samples to avoid environmental contamination. In addition, few studies have been conducted on correlating the presence and timing of M. hyopneumoniae in the nasal cavity with clinical pneumonia. Quantitative assays will need to be developed to enable to better understand this process.
Several other limitations of the study include study design (cross-sectional vs. prospective), the lack of correlation between PCR and serological results were discussed by the authors, indicating their awareness of these potential shortcomings. The information provided in this article will contribute further information concerning the pathogenesis of M. hyopneumoniae. The information gained from this study may aid in improving the development of and determination of timing or appropriate intervention strategies.
1. Stark KD, Nicolet J, Frey J. Detection of Mycoplasma hyopneumoniae by air sampling with a nested PCR assay. Applied and Environmental Microbiology. 1998;64:543-548.