Natural transmission and detection of Mycoplasma hyopneumoniae in a naïve gilt population

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Dr. Alyssa Betlach, member of the Maria Pieters Myco Lab, recently published a study on the natural transmission of Mycoplasma hyopneumoniae in Veterinary Microbiology. The study evaluated transmission rate in a naïve gilt population and compared various sample types to detect infection.

Methods

Researchers created a natural seeder by putting a naïve gilt in contact with two experimentally infected gilts. Once infection was confirmed, the natural seeder gilt was put in contact with a new population of 29 naïve gilts. This naïve population was then monitored for eight weeks. Multiple sample types were collected at 0, 1, 2, 4, 6, and 8 weeks post-contact with the natural seeder:

  • blood samples
  • laryngeal swabs
  • deep tracheal catheters
  • oral fluid sample for each pen

Indirect ELISA was used on blood samples while the remaining sample types were tested via PCR. At the end of the study, lungs were collected to evaluate gross and microscopic lesions as well as collect bronchial swabs, also tested by PCR.

Results

All the pen oral fluid samples remained negative throughout the duration of the study. Laryngeal swab and deep tracheal catheter samples from one gilt were positive six weeks post-contact with the natural seeder while the other 28 gilts remained negative. Eight weeks post-contact, one gilt had positive results for laryngeal swab, deep-tracheal catheter and bronchial swab; four gilts had both deep-tracheal catheter and bronchial swab positive results; three gilts only had a positive bronchial swab and the remaining 21 gilts were negative. One gilt was found seropositive in this study, at eight weeks post-contact. Therefore, from one infected animal, an average of 5.84 secondary infections in a group of naïve gilts, at 8 weeks post-contact.

This work confirms that the Mycoplasma hyopneumoniae spreads slowly and that the transmission rate is low. Additionally, it gives us more insight regarding the best sample type to detect this pathogen; deep-tracheal catheters being the most sensitive in this study.

Read the entire article to get more detail on transmission rate.

Abstract

Mycoplasma hyopneumoniae (M. hyopneumoniae) continues to be a prevalent and economically important swine respiratory pathogen. For M. hyopneumoniae surveillance, blood samples and/or oral fluids are commonly collected from incoming replacement gilts prior to entering sow farms. However, limitations to this approach exist, particularly due to low sensitivity during acute stages of natural infection, leading to diagnostic uncertainty. Therefore, the objective of this study was to evaluate the natural transmission and detection of M. hyopneumoniae based on the introduction of one infected gilt to a naïve population. Twenty-nine naïve gilts were housed with one M. hyopneumoniae naturally exposed gilt for 8 weeks. Deep tracheal catheters, laryngeal swabs, and blood samples were individually collected from each gilt at 0, 1, 2, 4, 6, and 8 weeks post-contact (wpc), along with one pen-based oral fluid sample. Blood samples were assayed by ELISA, while all other samples were tested by real-time PCR. The transmission rate of M. hyopneumoniae (ꞵ) was estimated using a Bayesian mixed-effects generalized linear model. At 8 wpc, 27 % (8/29) of the naïve gilts had become infected (ꞵ = 0.73 new infected gilts/gilt-week). Seroconversion was detected in 3% of contact gilts at 8 wpc. Oral fluids were negative for M. hyopneumoniae at all samplings. In this study, the natural transmission of M. hyopneumoniae was slow and detection varied based on sample type and timing. Thus, M. hyopneumoniae surveillance protocols should include lower respiratory tract samples that are tested by real-time PCR to avoid the introduction of potentially infected gilts into naïve sow farms.

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