By Guilherme Cezar, Kinath Rupasinghe, Daniel Linhares and Giovani Trevisan, Iowa State University

Mycoplasma hyopneumoniae is a prevalent and economically impactful respiratory pathogen causing enzootic pneumonia that results in a persistent, non-productive cough. The pathogenicity of MHP arises from its ability to adhere to and damage the ciliary epithelium in the respiratory tract’s trachea, bronch, and bronchioles. MHP causes decreased feed efficiency, reduced average daily gain and increased medication costs. MHP also plays a significant role in the porcine respiratory disease complex, interacting with other respiratory pathogens.

Therefore, the U.S. has discussed the elimination of this pathogen for several years, with several protocols being implemented to eliminate MHP from breeding herds. The SDRS has MHP data since 2002. As a result, the SDRS team identified detection trends over time, demonstrating trends from the U.S. industry toward eliminating this pathogen.

First, the percentage of positive submissions from breeding herds decreased substantially from 2021 (21.75%) to 2022 (13.5%) and has kept a lower level since then (Figure 1). However, the wean-to-market submissions had a peak in positivity since August 2024, which may be a concern regarding biosecurity for sow farms.

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Another piece of information supporting the industry’s MHP elimination trends is the percentage of samples submitted for MHP PCR testing. Since 2023, there has been a gradual increase in the usage of deep tracheal swabs (pink color in Figure 2), a sample type considered one of the most sensitive to screen pigs in breeding herds or gilt development units.

In addition, using Iowa State University data, the number of cases with a confirmed tissue diagnosis for MHP (cases where diagnosticians gather all the information as clinical history, tests performed, and microscopic and macroscopic lesions) decreased over time, reaching a record low number in 2024 (Figure 3).

As a result, the SDRS data documents progress in the industry’s efforts to eliminate MHP from breeding herds. Still, there is significant MHP activity to declare victory – efforts should remain to further reduce MHP impact in the U.S. swine herds. Particularly, there is a concern about the finishing sites still having increased positivity levels, which might indicate a possible biosecurity bridge issue. SDRS will keep monitoring MHP and other pathogens to inform the swine industry about pathogen activity in the U.S.