MYCOPLASMA HYOPNEUMONIAE (ENZOOTIC PNEUMONIA)
LEVELS: Highly unlikely: No controls necessary; Highly unlikely: No evidence of non-foodborne zoonotic transmission; Unlikely to be effective: One or more pathways of farm-to-farm transmission exist that cannot be controlled by on-farm biosecurity; Easy: Distinct clinical signs and/or existing test(s) available at local/regional laboratory(s); Substantial: Unsustainable acute or chronic losses related to severe clinical signs in a high prevalence of animals; Negligible: Little or no market disruption when disease occurs on one or more farms; Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments; Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy; Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations; Available but uncertain efficacy: Commercial or autogenous vaccines exist in the US but protection may be inconsistent; Possible: Eradication possible but likely to require major changes into logistic systems, regulatory environment, infrastructure, and producer behaviors
OVERVIEW
Mycoplasma hyopneumoniae is the etiological agent of enzootic pneumonia (EP) and a primary pathogen in the porcine respiratory disease complex (PRDC). It infects only pigs and causes long-term colonization of ciliated respiratory epithelium, damaging the mucociliary apparatus and interfering with innate and acquired immunity. This predisposes pigs to secondary bacterial infections (Pasteurella multocida, Streptococcus suis, Glaesserella parasuis) and potentiates viral infections (PRRSV, PCV2). EP is characterized by chronic bronchopneumonia with high morbidity, low mortality, and decreased production performance. The economic impact is primarily from decreased average daily gain (6-20% reduction), increased feed conversion ratio, and increased days to market—estimated at significant losses per affected pig. M. hyopneumoniae is present in virtually all countries where pigs are raised, except Switzerland and Norway which have completed national eradication programs. Transmission occurs via close nose-to-nose contact and is slow (1-2 naive pigs infected per infected pig over 4-6 weeks). Airborne transmission over short and long distances has been documented. Colonization persists for 7-8 months. Both commercial inactivated and live attenuated vaccines are available; vaccination improves performance but does not prevent colonization or significantly reduce transmission. Eradication is achievable through depopulation/repopulation, herd closure with medication, or partial depopulation protocols.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No controls necessary
M. hyopneumoniae is strictly host-specific. "The pathogen infects only pigs." There is no evidence of foodborne transmission to humans.
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No evidence of non-foodborne zoonotic transmission
M. hyopneumoniae infects only swine and has no zoonotic potential. No human infections have been documented.
EFFECTIVENESS OF ON-FARM BIOSECURITY IN PREVENTING FARM-TO-FARM TRANSMISSION
Level: Unlikely to be effective: One or more pathways of farm-to-farm transmission exist that cannot be controlled by on-farm biosecurity
Airborne transmission complicates biosecurity: (1) Airborne transmission documented: "airborne transmission of M. hyopneumoniae has been suspected for decades and has been shown over short...and long distances"; (2) Seasonal patterns: "herd reinfections with M. hyopneumoniae often occurred in the autumn and winter when atmospheric conditions favored aerosol transmission"; (3) Prolonged shedding: "Colonized pigs appear to be infectious to other animals during the entire duration of infection" (7-8 months); (4) Carrier introduction: "M. hyopneumoniae is most commonly introduced into naive populations by direct transmission through the introduction of infected pigs."
DIFFICULTY OF DETECTING AND CONFIRMING INFECTION
Level: Easy: Distinct clinical signs and/or existing test(s) available at local/regional laboratory(s)
Multiple diagnostic methods are readily available: (1) Clinical signs suggestive: "Nonproductive cough and decreased growth rate are suggestive of M. hyopneumoniae infection"; (2) PCR widely used: "high accuracy, fast turnaround, high throughput...have made real-time PCR the most-used confirmatory test"; (3) Serology available: "Various enzyme‐linked immunosorbent assays (ELISAs) are commercially available"; (4) Slaughter evaluation: "Evaluation of lungs at slaughter has been used to collect samples for confirmatory testing"; (5) Histopathology characteristic: Bronchointerstitial pneumonia with hyperplasia of bronchus-associated lymphoid tissue.
FINANCIAL IMPACT ON FARM'S COST OF PRODUCTION
Level: Substantial: Unsustainable acute or chronic losses related to severe clinical signs in a high prevalence of animals
EP causes substantial economic losses: (1) Performance reduction: "Chronically affected pigs have an average reduction in daily weight gain of 6–20%"; (2) Multiple impacts: "The economic impact of EP is significant and primarily related to decreased average daily gain, increased feed conversion ratio, and increased number of days to reach market weight"; (3) Near-universal prevalence: "M. hyopneumoniae is found worldwide in nearly all countries and pig farms where the organism has not been intentionally eliminated"; (4) PRDC contribution: "M. hyopneumoniae is also one of the major pathogens involved in the PRDC."
EFFECT ON DOMESTIC OR EXPORT MARKETS
Level: Negligible: Little or no market disruption when disease occurs on one or more farms
No trade implications: (1) Not regulated: EP is not a reportable or trade-restricted disease; (2) Endemic worldwide: Present in virtually all pig-producing countries; (3) Production disease: Impact is on farm economics, not trade.
PATHOGEN'S ABILITY TO DEVELOP AND SPREAD RESISTANCE
Level: Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments
No significant resistance documented: (1) Natural resistance only: "Mycoplasma hyopneumoniae shows an intrinsic resistance to beta-lactam antibiotics, sulfonamides, and trimethoprim" (due to lack of cell wall); (2) Stable susceptibility: "de Jong et al. (2021) found similar minimal inhibitory concentration (MIC) results of 13 antimicrobial agents during 2015–2016 compared to 2010–2012"; (3) Some reduced susceptibility: "Some studies have reported reduced susceptibility of M. hyopneumoniae field strains to tetracyclines, macrolides, lincosamides, or fluoroquinolones" but clinical breakpoints not established.
AMR DEVELOPMENT DRIVEN BY DISEASE MANAGEMENT
Level: Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy
Vaccination is primary control method: (1) Vaccines widely used: "Vaccination is widely applied worldwide to control M. hyopneumoniae infections"; (2) Antimicrobials not first line: "Improvement of management practices is essential for the control"; (3) Treatment limitations: "Although treatment may lead to clinical improvement, clinical signs of EP and shedding of M. hyopneumoniae typically reappear after cessation of therapy"; (4) Eradication programs: Medication used strategically for eradication, not routine control.
AVAILABILITY OF EFFECTIVE TREATMENT OPTIONS
Level: Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations
Multiple antimicrobial classes are effective: (1) Effective drugs: "Potentially active antimicrobials against M. hyopneumoniae include tetracyclines, macrolides, lincosamides, pleuromutilins, amphenicols, aminoglycosides, aminocyclitols, and fluoroquinolones"; (2) Performance improvement: "most agents...improved clinical parameters (clinical signs, lung lesions) and reduced performance losses"; (3) Does not clear infection: "Antimicrobials may not prevent infection or eradicate the bacterium from the respiratory tract but reduce the number of M. hyopneumoniae organisms."
AVAILABILITY OF EFFECTIVE VACCINES OR BACTERINS
Level: Available but uncertain efficacy: Commercial or autogenous vaccines exist in the US but protection may be inconsistent
Vaccines improve performance but have limitations: (1) Commercial vaccines available: "Commercial vaccines mostly consist of inactivated, adjuvanted whole-cell preparations"; attenuated vaccines licensed in Mexico and China; (2) Performance benefits: "Vaccination improves daily weight gain (2–8%), feed conversion ratio (2–5%), and sometimes mortality rate"; (3) Does not prevent colonization: "currently used vaccines reduce the number of organisms...decrease the prevalence of infection...However, vaccination does not significantly reduce the transmission"; (4) Incomplete protection: "protection against clinical pneumonia is often incomplete and vaccination does not prevent colonization."
FEASIBILITY OF ERADICATING THE DISEASE FROM THE US
Level: Possible: Eradication possible but likely to require major changes into logistic systems, regulatory environment, infrastructure, and producer behaviors
Eradication is achievable with demonstrated success: (1) National eradication achieved: "M. hyopneumoniae is found worldwide...except Switzerland and Norway, where the overall prevalence is under 1% after completing eradication programs at the national level"; (2) Multiple methods: "Besides depopulation and repopulation...partial depopulation, herd closure and medication, and herd medication without closure are frequently practiced"; (3) High success rates: "Herd closure and medication have been shown to provide a high success rate"; (4) Ongoing programs: Diagnostic approaches specifically focused on eradication scenarios support efforts.