Mycoplasma hyosynoviae
LEVELS: Highly unlikely; No human illness; Already in the herd; Laboratory-dependent; Moderate; Negligible; Some; Available but inconsistent
| Register id | mycoplasma_hyosynoviae |
| Type | bacteria |
| Scientific name | Metamycoplasma hyosynoviae |
| NCBI taxid | 29559 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Mycoplasma hyosynoviae is a normal inhabitant of the tonsils and upper airway of pigs that occasionally spreads through the body and settles in joints, producing acute lameness in growers and finishers around three to five months old. It infects only pigs. Carriage is uncommon at weaning and peaks between ten and sixteen weeks; only a proportion of colonised pigs ever go lame, and what triggers the change is not known. Affected animals are suddenly lame in one or more limbs with soft, fluid joint swellings, and pigs with painful stifles or hocks may sit like a dog. The lameness usually resolves on its own over time unless something else, such as osteochondrosis, complicates it. Even so it matters — it is a genuine welfare problem and a cause of culling and mortality in the finishing barn. No commercial vaccine exists; autogenous vaccines have been tried with little published field data, so treatment, started early, is the usual approach.
C1 Zoonotic potential
Likelihood of transmission from pigs to humans
Highly unlikely: Human infection with the agent has never been reported, or has been reported but is not attributed to pig or pork exposure
Basis. ch53 53.4, first paragraph: "Mycoplasma hyosynoviae, also belonging to the class Mollicutes, INFECTS ONLY SWINE. It is a commensal of the tonsils, nasal cavity, and conducting airways, and occasionally invades systemically to produce acute non-purulent arthritis in growing- and finishing-age swine." The chapter gives a Public Health section to M. hyorhinis alone and says nothing about human infection with this species.
How this level was decided
Level 1, on a stated host restriction rather than a silence. The chapter says the organism infects only swine in its opening sentence, and it demonstrates in the neighbouring section that its authors raise public health where they consider there is a question.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
Basis. No human illness with M. hyosynoviae is described anywhere in chapter 53; the organism "infects only swine" (53.4).
How this level was decided
Level 1. An organism that infects only swine cannot be a source of human illness from pigs, which is what C2 grades after the 2026-09-01 rescoping.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Already in the herd: Present in most herds, or carried by pigs themselves, so there is no introduction event to prevent
Basis. ch53 53.4: "It is A COMMENSAL of the tonsils, nasal cavity, and conducting airways." 53.4.2: "the prevalence of colonization is low at weaning and typically peaks between 10 and 16 weeks of age. SIXTY PERCENT OF SOWS TESTED POSITIVE for M. hyosynoviae by PCR, while their progeny tested negative at 1-2 days of age, and 13% of the piglets tested positive at 3 weeks of age. In another report, 55% OF TONSILLAR SWABS FROM DAMS WERE PCR POSITIVE, 1 week post farrowing... At 3 weeks post farrowing, M. hyosynoviae was detected in tonsillar swabs from 48.3% of dams." 53.4.3: "Tonsils are the primary site of colonization and PIGS CAN BECOME PERSISTENT CARRIERS."
How this level was decided
Level 1. Around half to sixty percent of sows in the studies cited are carrying it in their tonsils, pigs become persistent carriers, and colonisation peaks in the grower phase on the farm rather than arriving from anywhere. There is no introduction event to prevent: the reservoir is the resident breeding herd. The chapter proposes no exclusion measure of any kind, which is consistent -- it discusses prevention entirely in terms of treating the arthritis, not keeping the organism out.
C4 Detection difficulty
Difficulty of recognizing and confirming infection
Laboratory-dependent: The presentation does not point to this disease specifically, but local or regional laboratories can confirm it with a validated assay once it is suspected
Basis. ch53 53.4.7: "Mycoplasma hyosynoviae should be suspected in cases of acute lameness in fattening pigs older than 10 weeks, ALONG WITH OTHER INFECTIOUS CAUSES OF LAMENESS. Noninfectious causes such as osteochondrosis dissecans and nutritional imbalances, as well as genetics, trauma, management practices, and facilities design, among others, should be evaluated as part of an exhaustive lameness investigation." "Diagnosis requires demonstration of characteristic lesions and confirmation of M. hyosynoviae infection IN AFFECTED JOINTS. Acutely lame, NON-MEDICATED pigs should be selected for sampling... Gross and microscopic lesions in synovial membranes are suggestive of M. hyosynoviae infection, BUT NOT PATHOGNOMONIC." "Confirmation by culture is only practiced in selected diagnostic laboratories, due to the intrinsic lack of sensitivity, and HAS BEEN RAPIDLY REPLACED BY DETECTION WITH HIGHLY ACCURATE PCR-BASED TESTS." 53.4.2 adds the interpretive limit: "There is NO EVIDENCE that the detection of M. hyosynoviae in the tonsils or the oral fluids CORRELATES WITH THE CLINICAL OUTCOME at the pen level."
How this level was decided
Level 2. A highly accurate PCR exists and has replaced culture, which puts the assay in ordinary diagnostic laboratories and rules out levels 3 and 4. What holds it off level 1 is that lameness in a finishing pig is one of the least specific presentations in swine medicine -- the chapter sends the investigator through osteochondrosis, nutrition, genetics, trauma and facility design before this organism -- and that the easy samples are worthless: tonsil and oral fluid positives do not correlate with disease, so the diagnosis needs joint fluid and synovial membrane from an acutely lame pig that has not been medicated.
C5 Production cost
Financial impact on the infected farm's cost of production
Moderate: Losses measurably increase cost of production but remain manageable within normal farm operations, whether acute, chronic, or associated with endemic disease
Corrected by Eric from L2 Minor. Reason: "c5l3, i think this is an exemplar for c5. Unless a farm has eradicated it, even with vaccination and strategic medication, it tends to be persistent but quantifiable but manageable cost on production"
Basis. ch53 53.4.5: "The main clinical sign is acute lameness affecting one or more joints in pigs 3-5 MONTHS OF AGE... Lame pigs are often reluctant to walk or to bear weight on the lame limb. LAMENESS TYPICALLY DECREASES WITH TIME UNTIL THERE IS FULL RECOVERY unless complicated by conditions like osteochondrosis that can aggravate and extend lameness. Pigs have decreased appetite or are reluctant to move, which results in poor body condition. Thus, infections with M. hyosynoviae CAN BE A SIGNIFICANT WELFARE ISSUE AND CONTRIBUTE TO THE GENERAL CULLING AND MORTALITY OBSERVED IN FINISHING PIGS." 53.4.2: "Lameness and lesions of arthritis are produced in ONLY A PORTION of colonized pigs." No morbidity, mortality or cost figure is given.
How this level was decided
Level 2, and FLAGGED AS A LEVEL 2 OR 3 JUDGMENT, for the same reason as M. hyorhinis and with the same missing numbers. Level 2 is scored on the chapter's own word "full recovery": most affected pigs get better, only a portion of colonised pigs are affected at all, and there is no claimed mortality -- small and generally short-lived losses. THE LEVEL 3 ARGUMENT IS ABOUT WHICH PIGS ARE LOST. This disease hits at 3 to 5 months, so a pig that is culled has already had most of the feed put into it, and the chapter says outright that the condition contributes to culling and mortality in finishing pigs. A cull at 5 months is a materially different loss from a nursery cull, and if it is common in US finishing barns the answer is level 3. The chapter does not say how common it is; Eric will know.
C6 Market impact
Duration of material disruption to pork and pig markets
Negligible: Little or no material disruption to supply or demand when disease occurs on one or more farms
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c6l1, no impact on markets"
Basis. A commensal of the pig tonsil carried by around half of sows, causing sporadic lameness in finishers. No trade measure, movement control or consumer response is recorded in section 53.4.
How this level was decided
INFERRED. Under the standing note SCORING/market_impact, an endemic organism diagnosed routinely in US herds with no market move on record is level 1.
C7 Treatment potential
Potential for treatment to improve outcomes
Some: Treatment exists but is inconsistent, requires extralabel use, or works only in some circumstances
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c7l2, labelled products availabale but with uncertain efficacy"
Basis. ch53 53.4.8: "ANTIMICROBIAL TREATMENTS ARE THE MOST COMMON STRATEGY for disease control. M. hyosynoviae isolates have been shown to be sensitive to tetracyclin, tiamulin, valnemulin, linomycin, gentamycin, enrofloxacin, and danofloxacin. THERE IS A RANGE OF SENSITIVITY, with some isolates being overall more resistant while others appear more susceptible. TO BE EFFECTIVE, TREATMENT SHOULD BE INITIATED EARLY DURING INFECTION." 53.4.7 records the practical consequence of that last clause: diagnosis requires sampling acutely lame pigs that have NOT been medicated, so treating early and confirming the diagnosis pull against each other.
How this level was decided
Level 2, and this is the cell where the label question matters most in the batch. Antimicrobials work and are the mainstay, so it is not level 3. Whether it is level 1 or level 2 depends on whether a US product names this species: lincomycin is used against swine arthritis and would be the candidate, and the US tiamulin label -- which Eric has already quoted in full -- names Lawsonia and B. hyodysenteriae and NOT M. hyosynoviae. FLAGGED FOR ERIC UNDER THE RULE HE SET ON THE TIAMULIN LABEL: "Ask me when it is not clear and I will decide." The US label text is not in the folder, so the species question is not decidable from the evidence here. Level 2 is scored, and it does not rest on the label alone: the chapter reports a range of sensitivity between isolates, and treatment works only if started early, which is difficult when the diagnosis needs an unmedicated pig. Both are the level 2 clause "works only in some circumstances".
C8 Vaccine availability
Availability of effective vaccines or bacterins
Available but inconsistent: Commercial or autogenous vaccines exist in the US but protection may be inconsistent
Corrected by Eric from L3 Needed but not available. Reason: MOVED L3 -> L2 ON HIS FIELD KNOWLEDGE, AGAINST THE CHAPTER, AND HE CONFIRMED IT WHEN SHOWN THE CONFLICT. He wrote "c8l2, a number of pretty good vaccines are commercially available but can be uncertain in their efficacy, usually based on vaccine timing and maternal antibody interference. Amongst vet vaccines, these are some of the better ones, but can be challenging to get timing right." The cell was held rather than written, because ch53 53.4.8 says the opposite in terms: "No commercial vaccine for the prevention of disease caused by M. hyosynoviae has been developed... In one field trial, an autogenous M. hyosynoviae vaccine could not successfully prevent the development of lameness in finishing pigs." He was shown that sentence, shown that the timing and maternal-antibody discussion in the chapter belongs to M. hyopneumoniae at 53.2.10, and shown that the ruling inverts his own M. hyorhinis C8 L3 on the facing page -- and he chose level 2 on his own knowledge of what is in use in US herds. THE LEVEL 2 LABEL FITS HIS DESCRIPTION EITHER WAY: it reads "commercial OR AUTOGENOUS vaccines exist in the US but protection may be inconsistent", so only the word "commercial" conflicts with the chapter, not the level. RECORDED AS RESTING ON HIS FIELD KNOWLEDGE RATHER THAN ON 53.4.8, so that anyone reading the chapter and the score together can see why they differ.
Basis. ch53 53.4.8: "NO COMMERCIAL VACCINE for the prevention of disease caused by M. hyosynoviae HAS BEEN DEVELOPED. Manufacturers and producers have used autogenous vaccines, but FIELD TRIAL DATA ARE LIMITED. IN ONE FIELD TRIAL, AN AUTOGENOUS M. HYOSYNOVIAE VACCINE COULD NOT SUCCESSFULLY PREVENT THE DEVELOPMENT OF LAMENESS IN FINISHING PIGS (Lauritsen et al. 2013)."
How this level was decided
Level 3, and FLAGGED AS A LEVEL 2 OR 3 JUDGMENT sitting beside the M. hyorhinis C8 cell, which was scored level 2 on almost the same sentence. THE DIFFERENCE BETWEEN THEM IS ONE FIELD TRIAL. For M. hyorhinis, autogenous products are popular and have never been evaluated -- unknown efficacy, which is level 2. Here an autogenous vaccine WAS put in a field trial and did not prevent lameness, which is a tested failure rather than an open question, and that is the pattern already recorded at level 3 for Brachyspira pilosicoli, where an autogenous bacterin raised antibody and still let the pigs scour. On the second half of the level 3 test, the disease would justify vaccinating: the chapter calls it a significant welfare issue contributing to culling and mortality in finishing pigs, and the only alternative is antimicrobials that have to be started before the diagnosis can be confirmed. IF ERIC READS THE ONE NEGATIVE TRIAL AS TOO THIN to distinguish this from M. hyorhinis, both cells go to level 2 together.
Levels and evidence are generated from data/assignments/mycoplasma_hyosynoviae.yml; the overview is authored in data/overviews/mycoplasma_hyosynoviae.md. Do not hand-edit this page — corrections go in data/assignments/CORRECTIONS.yml.
Quoted material marked Basis is from Zimmerman JJ, Karriker LA, Ramirez A, Schwartz KJ, Stevenson GW, Zhang J, eds. Diseases of Swine, 12th edition. Hoboken: Wiley Blackwell, 2025 — except where another source is named in the quotation itself.