M. hyopneumoniae

M. hyopneumoniae Full Name

Mesomycoplasma hyopneumoniae

M. hyopneumoniae Introduction

Mycoplasma hyopneumoniae is the primary etiological agent of enzootic pneumonia (EP) in swine, a chronic respiratory disease that causes significant economic losses to the global pork industry through reduced growth rates, increased feed conversion ratios, increased susceptibility to secondary infections, and costs associated with treatment and prevention. This cell wall-deficient bacterium colonizes the ciliated epithelium of the porcine respiratory tract, causing ciliostasis, loss of cilia, and epithelial cell damage that compromises pulmonary defense mechanisms and predisposes animals to secondary bacterial infections, particularly with Pasteurella multocida, Actinobacillus pleuropneumoniae, and Streptococcus suis. The disease is characterized clinically by a chronic, dry, non-productive cough, reduced weight gain, and poor feed efficiency, with pathological findings including cranioventral pulmonary consolidation with a characteristic purple-gray discoloration. M. hyopneumoniae is a key component of the porcine respiratory disease complex (PRDC), a multifactorial syndrome involving interactions between various viral (PRRSV, PCV2, swine influenza virus) and bacterial pathogens that collectively cause severe respiratory disease in growing pigs.

The pathogenesis of M. hyopneumoniae infection involves attachment to ciliated respiratory epithelial cells via surface adhesins, followed by induction of ciliostasis, epithelial damage, and modulation of host immune responses. Several adhesins have been identified, including P97 (Mhp183), P102 (Mhp182), P159 (Mhp494), and P146 (Mhp683), which mediate binding to glycosaminoglycans, fibronectin, and other host cell surface molecules. Following attachment, M. hyopneumoniae induces loss of cilia and epithelial cell death through mechanisms that are not fully understood but may involve production of hydrogen peroxide, ammonia, and other toxic metabolites. The organism also modulates host immune responses, inducing production of proinflammatory cytokines (IL-1, IL-6, TNF-α) while simultaneously evading immune clearance through antigenic variation of surface lipoproteins and suppression of lymphocyte proliferation. This immune modulation contributes to the chronic nature of infection and the development of lymphoid hyperplasia (cuffing pneumonia) characteristic of enzootic pneumonia. Transmission occurs primarily through direct contact with infected pigs or aerosol spread over short distances, with sows serving as the primary source of infection for piglets.

Diagnosis of M. hyopneumoniae infection relies on clinical signs, pathological findings, serology, and molecular detection methods. Serological tests including ELISA detect antibodies to M. hyopneumoniae antigens and are useful for herd-level monitoring but cannot distinguish between infected and vaccinated animals (unless DIVA vaccines are used) and may not detect early infection before seroconversion. PCR-based methods targeting specific genes (e.g., P36, P46, 16S rRNA) provide improved sensitivity for detecting M. hyopneumoniae in respiratory samples and can identify subclinical infections in apparently healthy animals. Control of M. hyopneumoniae infection involves a combination of management practices (all-in/all-out production, improved ventilation, reduced stocking density), vaccination, and strategic antimicrobial use. Commercial bacterin vaccines reduce clinical signs, lung lesions, and performance losses but do not prevent colonization or eliminate the organism from infected herds, and vaccinated animals can still transmit infection. Antimicrobials effective against M. hyopneumoniae include macrolides (tilmicosin, tulathromycin, tylosin), tetracyclines, lincosamides, pleuromutilins (tiamulin, valnemulin), and fluoroquinolones, administered either therapeutically or as in-feed medication for control. Eradication programs based on herd closure, medication, and partial or complete depopulation-repopulation have been implemented in some regions with variable success. The development of improved vaccines, including subunit vaccines based on conserved adhesins and DIVA-compatible formulations, remains an active area of research.

Alternate Names for M. hyopneumoniae

Mesomycoplasma hyopneumoniae; M. hyopneumoniae