It should come as no surprise that Mycoplasma hyopneumoniae continues to frustrate swine producers and veterinarians. Herds infected with this bacterium develop chronic bronchopneumonia, referred to as enzootic pneumonia and on average results in losses of $0.63 to $10.12 per market pig. With such a high economic burden, the industry has begun to aggressively implement M. hyopneumoniae control and elimination programs. Removal of this agent from our herds results in healthier pigs, reduced use of antimicrobials and improved herd productivity.

This elusive pathogen lives in the lower respiratory tract, specifically the trachea. What this means for us, is that detecting this bacterium is not as straight forward as collecting a serum sample for porcine reproductive and respiratory syndrome virus polymerase chain reaction. Tracheal samples, laryngeal samples and oral fluids can be used to detect the presence of the pathogen, while serum samples can be used to detect exposure. There are costs and benefits to each of these sampling modalities (How-to video for tracheal sampling available here). 

In addition to tracheal samples, laryngeal samples can be also collected, however diagnostic sensitivity is compromised. As for oral fluids, detection of M. hyopneumoniae has been variable at a low prevalence. Serum is another common sample type for M. hyopneumoniae detection, however, we are targeting antibodies which are only produced at detectable levels about one month after exposure.

As with any pathogen, the success of control and elimination programs is directly correlated to how well we can detect disease. For M. hyopneumoniae, detection is complicated because of where this bacteria lives, how slowly its spreads in a herd and limitations of current diagnostics. In the words of veterinarian Michelle Sprague, "it feels like we are chasing a ghost."

To address part of this puzzle, a multi-institutional collaboration between academia, industry and a swine production system was formed to develop novel guidelines for M. hyopneumoniae surveillance based on different samples types, sample sizes and prevalence.

The study was conducted in one room (46 pens, ~28 pigs per pen, ~1250 pigs) of a wean-to-finish site sourced with 21-day-old MHP-negative barrows. A centrally located pen was selected and 10 seeder pigs were intratracheally inoculated with M. hyopneumoniae. After inoculation, all pens were sampled (tracheals, serum and oral fluids) every two weeks, for 98 days. The field data (7 sampling points, 315 tracheals, 315 oral fluids, 1258 sera collected) was used to model probability of detection estimates by sample type, sample size and prevalence at the herd and pen level. To evaluate detection of M. hyopneumoniae, we focused on two scenarios. Scenarios estimated probability of detection over time, given one or five positive pigs in one pen in a population. Multiple sample sizes were evaluated to compare what sample type was the most effective for early detection of M. hyopneumoniae. Table 1 shows a subset of results provided by the model.

Probability of detection estimates over time by sample type and size for scenarios 1 and 2.

Results show that tracheal samples provide the earliest detection, especially at large sample sizes. For example, if the initial infection starts with five pigs, with 90 tracheal samples, there is a 60% chance that you will detect M. hyopneumoniae seven days post infection. However, tracheal samples are challenging to collect, involve more pig handling, and are five times more expensive than testing serum. While serum remains a robust, economical and practical to collect, the delayed immune response limits its use for early detection. For example, it is only after 42 DPI that serum provides a 50% chance of detecting M. hyopneumoniae.  Similarly, for both scenarios and sample sizes (30 or 90), there was greater than 50% chance of detecting M. hyopneumoniae using oral fluids at 42 DPI. These data show that oral fluids might not be an appropriate sample for early detection of the agent. However, routine collection of oral fluids in known positive populations may provide an economical and welfare-friendly solution for monitoring M. hyopneumoniae

In summary, a combination of population based serology, tracheal swabs and oral fluids will be part of novel surveillance protocols for effective detection of M. hyopneumoniae. Probability of detection estimates by sample size and type are now available for M. hyopneumoniae and will significantly improve surveillance for­­ this "Waldo" of a pathogen. 

Co-authors are: Seth Krantz, Tosh Farms; Dapeng Hu, Chong Wang, Thairê Pereira Maróstica, Alexandra Henao-Diaz and Jeffrey Zimmerman all with Iowa State University; Eduardo Fano and Dale Polson, Boehringer Ingelheim; Edgar Tapia and Silvia Zimmerman, IDEXX Laboratories; AW Tucker, Pig Improvement Company and University of Cambridge; Deanne Hemker and J.P Cano, Pig Improvement Company.

References:
1. Haden DC, Painter T, Fangman T, et al. Assessing production parameters and economic impact of swine influenza, PRRS and Mycoplasma hyopneumoniae on finishing pigs in a large production system. In: Proceedings 43rd Annual Meeting Am Assoc Swine Veterinarians, Denver, Colorado. 2012:75–76.

2. Sponheim A, Alvarez J, Fano E, Schmaling E, Dee S, Hanson D, Wetzell T, Pieters M. Comparison of the sensitivity of laryngeal swabs and deep tracheal catheters for detection of Mycoplasma hyopneumoniae in experimentally and naturally infected pigs early and late after infection. Veterinary Microbiology. 2020 Feb 1;241:108500.

3. Holst S, Yeske P, Pieters M. Elimination of Mycoplasma hyopneumoniae from breed-to-wean farms: A review of current protocols with emphasis on herd closure and medication. J Swine Health and Prod. 2015;23:321-330.

Source: Marisa Rotolo and Maria Jose Clavijo, who are solely responsible for the information provided, and wholly owns the information. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.