Infectious Anemia
LEVELS: Highly unlikely; No human illness; Routine biosecurity keeps it out; Laboratory-dependent; Minor; Negligible; Some; Available, or not needed
| Register id | mycoplasma_suis |
| Type | bacteria |
| Scientific name | Mycoplasma suis |
| NCBI taxid | 57372 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Mycoplasma suis, once called Eperythrozoon suis, is unlike the other pig mycoplasmas: it attaches to and invades red blood cells, destroying them and causing infectious anaemia. It cannot be grown on laboratory media. Acute disease shows as pallor, fever, jaundice and blue extremities; chronic infection is subtler, showing only as unthriftiness and poor growth, and in sows can cause fever, inappetence, failure to milk and poor mothering in the days after farrowing. The defining feature is persistence — pigs that recover become long-term subclinical carriers, and those carriers are the reservoir, with disease flaring again when something suppresses immunity. Most transmission is by blood: contaminated needles and surgical instruments, across the placenta, in semen, and possibly by biting insects. Diagnosis is by PCR, which is more sensitive than looking at a blood smear, backed by serology. Oxytetracycline controls clinical disease but does not clear the organism, and there is no vaccine, so prevention comes down to changing needles between litters and avoiding blood transfer.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c1l1, no evidence that pigs are a credible source of human infection"
Basis. Chapter 53 contains one Public Health section, 53.3.2, and it belongs to M. hyorhinis. Section 53.5 on M. suis runs to etiology, epidemiology, pathogenesis, clinical signs, diagnosis, treatment and prevention and mentions human infection nowhere. 53.5.2 lists the hosts and reservoirs it does recognise -- carrier pigs as "the main reservoirs of infection", wild boar in Germany (10%) and Brazil (50%) -- and no other species appears.
How this level was decided
INFERRED FROM A STRUCTURED SILENCE, and the silence is weaker here than on M. hyopneumoniae and M. hyosynoviae, which is why the support flag differs. Those two carry an explicit statement that the organism infects only pigs; this section makes no host-range claim at all. What supports level 1 is that the authors demonstrably write a public health section where they think one is warranted, and did not write one here, plus an epidemiology section that identifies pigs and wild boar as the reservoirs and nothing else. FLAGGED HONESTLY: haemotrophic mycoplasmas of other host species have been reported from immunocompromised people in the wider literature, which this chapter does not engage with, so level 1 records what the folder holds rather than a settled negative.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c2l1, no evidence of human infection"
Basis. No human illness with M. suis is described anywhere in chapter 53.
How this level was decided
INFERRED, following C1. Under C2 as rescoped, level 1 means pigs are not a source of human illness with this agent, and nothing in the folder says otherwise. It moves with C1 if the folder ever gains a source that engages with the question.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Routine biosecurity keeps it out: Quarantine of incoming stock, transport and fomite control, cleaning and disinfection, and the usual monitoring reliably exclude it
Corrected by Eric from L4 Extraordinary biosecurity required. Reason: "c3l3, true we don't completely undestand the epidemiology of this disease but we do know herds can remain free of it with routine biosecurity, especially indoors. Insufficient data about the disease in outdoor settings but I am very happy with L3 here."
Basis. ch53 53.5.2: "A HALLMARK OF M. SUIS INFECTION IS THE LONG-TERM PERSISTENCE IN SUBCLINICALLY INFECTED PIGS, THESE CARRIERS BEING THE MAIN RESERVOIRS OF INFECTION. The reactivation of disease can be triggered by immunosuppression." "THE NATURAL TRANSMISSION ROUTES OF M. SUIS ARE LARGELY UNKNOWN." Potential routes listed: vertical (intrauterine), blood-contaminated semen, and "transmission by blood-sucking arthropods". Risk factor data from 69 Chinese farms: "The PRESENCE OF MOSQUITOES AND FLIES (ODDS RATIO 5.99) was associated with a higher prevalence", while antimicrobial treatment and frequency of disinfection were associated with lower prevalence. "M. suis has also been DETECTED BY PCR IN WILD BOARS in Germany (10%) and in Brazil (50%)." 53.5.6.2: "Transmission by needles and surgical instruments must be minimized by changing needles between sows and litters... STRATEGIES FOR THE ELIMINATION OF M. SUIS FROM INFECTED HERDS ARE NOT AVAILABLE. If a herd is M. suis-free, new additions should also be from herds that are negative for the organism." 53.5.5 on finding carriers: PCR and qPCR "are effective for the detection of carriers or subclinically infected pigs", but serology gives "frequent false negative results" because antibody titres persist only 2-3 months.
How this level was decided
Level 4, and FLAGGED AS A LEVEL 4 OR 5 JUDGMENT with the argument set out both ways, because it is the same shape as the ASF and pseudorabies reasoning Eric has already ruled on. LEVEL 4 IS SCORED because the barrier that has to be built is the L4 label almost item by item: the reservoir is subclinical lifelong carriers whose antibody disappears within two to three months, so keeping the organism out means repeated PCR testing of incoming stock to find animals that show nothing -- "repeated costly testing to find carriers, and may still fail" -- plus needle and instrument discipline at every injection, plus screening semen. The chapter says elimination strategies do not exist, and that a negative herd can only stay negative by sourcing from negative herds. THE LEVEL 5 ARGUMENT is that two of the L5 label's own listed reservoirs are in evidence: wild boar carry it at 10% in Germany and 50% in Brazil, and mosquitoes and flies carry an odds ratio of 5.99 for herd prevalence. US feral swine are abundant and there is no reason to think they would differ from German or Brazilian wild boar. WHAT HOLDS THAT BACK is that the chapter calls the natural transmission routes largely unknown and lists arthropod transmission as potential rather than demonstrated -- an odds ratio for the presence of flies is not vector competence -- and gives no US wild boar data at all. Under the standing note, L5 asks whether a reservoir outside the industry exists or WOULD ESTABLISH, and on this evidence that is arguable rather than shown.
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 53.5.4: the clinical picture is anaemia -- "Pallor, fever, occasional icterus, and cyanosis of the extremities, especially the ears" in acute disease; more commonly "mild anemia, increased mortality, and poor growth rates"; in sows "fever, anorexia, lethargy, dysgalactia, and poor maternal behavior". "The incubation period in naturally infected animals is highly variable with SOME INFECTED PIGS NEVER EXHIBITING CLINICAL DISEASE." 53.5.1: "The organism CANNOT BE CULTURED in cell-free media to date." 53.5.5: "Since isolation is not possible, pathogen detection relies on PCR assays or blood smears. Nowadays, there are SEVERAL PCR AND QUANTITATIVE PCR ASSAYS AVAILABLE THAT ARE MORE SENSITIVE for the detection of M. suis than blood smears... They are effective for the detection of carriers or subclinically infected pigs." Serology by recombinant-antigen ELISA exists but "antibody titers may persist only 2-3 months resulting in FREQUENT FALSE NEGATIVE RESULTS."
How this level was decided
Level 2. The presentation does not point here -- pallor, fever and poor growth are the least specific findings in a nursery, and dysgalactia in a sow has a long differential -- so this is not level 1. But under C4 as reworded the question is whether a validated assay exists and where it runs, and qPCR for M. suis is described as available, more sensitive than the alternative, and good enough to find subclinical carriers. That is ordinary diagnostic laboratory work. NOTE THAT THE ORGANISM CANNOT BE CULTURED AT ALL, which removes the fallback every other entry in this batch has and makes the PCR the whole diagnosis; and note that serology should not be used to rule infection out, because titres fade within months.
C5 Production cost
Financial impact on the infected farm's cost of production
Minor: Small and generally short-lived losses with little effect on overall cost of production
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c5l2, yes the disease will cause clinical disease and losses but the infection at both an individual and herd level can be managed, and eradicated"
Basis. ch53 53.5.4: "M. suis infection under field conditions CAN CAUSE ACUTE HEMOLYTIC DISEASE AND DEATH in young pigs, prepartum sows, and stressed weaned and feeder pigs... MORE COMMONLY, MILD ANEMIA, increased mortality, and poor growth rates are observed in suckling, weaned, and feeder pigs. Infection of sows may result in fever, anorexia, lethargy, DYSGALACTIA, and poor maternal behavior. Clinical disease in sows typically occurs within 3-4 days of introduction to the farrowing room or immediately after farrowing." "Chronic infections in animals with low or undetectable numbers of M. suis result in unthriftiness, pallor, and occasionally skin hypersensitivity"; chronic infection in sows has been associated with increased stillbirths, but "these findings deserve further investigation as inconclusive results have been obtained". 53.5.6.1 gives the one field-scale figure, from a US report: "Chlortetracycline fed to the entire sow herd at 22 mg/kg daily for 2 weeks RESULTED IN A NEARLY COMPLETE DISAPPEARANCE OF DYSGALACTIA IN SOWS farrowing within 5 weeks after the start of treatment (Strait et al. 2012)." No US prevalence figure appears; the prevalence data are German, Brazilian and Chinese.
How this level was decided
Level 2, and FLAGGED FOR ERIC AS A LEVEL 2 OR 3 JUDGMENT that turns on how often this is actually diagnosed in US herds, which the chapter does not say. Level 2 is scored under the standing note SCORING/production_cost_impact, which says to score against modern US production rather than the clinical picture the chapter paints: most infections are subclinical, the severe experimental disease requires splenectomised pigs, and the field losses described -- mild anaemia, poor growth, dysgalactia -- respond to a two-week course of chlortetracycline. Small and generally short-lived. THE LEVEL 3 ARGUMENT is the Strait paper itself, because dysgalactia across a whole sow herd that only resolved once the herd was medicated is a real and measurable production loss, and it is the one US observation in the section. The prevalence figures that would settle it are all foreign: 14% of German feeder pigs with 40% of farms positive, 96% of 69 Chinese farms, 76% of Brazilian sows in one study.
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, an old disease with no evidence of having a market impact"
Basis. Reported worldwide, endemic in carrier pigs, with no trade measure, movement control or consumer response recorded anywhere in section 53.5.
How this level was decided
INFERRED. Under the standing note SCORING/market_impact, an agent reported worldwide and present in US herds, with no market move on record, is level 1. Nothing about an anaemia of pigs reaches pork supply or demand.
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, i don't think there is a specfically labelled drug in the US so we will go with L2"
Basis. ch53 53.5.6.1: "THE TREATMENT OF CHOICE for infection IS OXYTETRACYCLINE administered parenterally. Acutely diseased pigs require parenteral treatment due to a lack of adequate feed consumption. Administration of oxytetracycline at times of stress or treatment in infected herds MAY HELP TO PREVENT ACUTE DISEASE. HOWEVER, TREATMENT DOES NOT NECESSARILY ELIMINATE THE ORGANISM FROM THE PIG, as M. suis may reside intracellularly in RBCs." Chlortetracycline fed to a whole sow herd for two weeks nearly abolished dysgalactia. "Supportive therapy and iron injections (200 mg iron dextran/pig) will help recovery and minimize mortality."
How this level was decided
Level 2. An effective treatment plainly exists -- the chapter names a drug of choice, it works well enough that a herd-level dysgalactia problem disappeared under it, and there is supportive therapy on top -- so this is nowhere near level 3. The question is level 1 or level 2, and it turns on two things. THE LABEL: whether a US oxytetracycline product names M. suis or eperythrozoonosis is not something the folder can answer. 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. THE SECOND POINT IS INDEPENDENT OF THE LABEL: the chapter says treatment does not necessarily clear the organism, because it hides inside the red cell, so treated pigs remain carriers and disease can reactivate under stress or immunosuppression. Treatment that controls the episode without clearing the infection is the level 2 clause "works only in some circumstances". If Eric rules the label names it, level 1 becomes arguable on the strength of the dysgalactia result.
C8 Vaccine availability
Availability of effective vaccines or bacterins
Available, or not needed: Effective vaccines are widely available in the US or secured for national outbreak response, or the disease does not clinically or economically justify vaccinating
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c8l1, no market imperative to develop a vaccine"
Basis. ch53 53.5.6.2: "NO COMMERCIAL VACCINE IS CURRENTLY AVAILABLE, and vaccine development is complicated by THE INABILITY TO CULTURE M. SUIS and the lack of knowledge of the virulence factors. An attempt to produce a vaccine from a recombinant protein produced in E. coli, while inducing a humoral and cellular immune response, FAILED TO PROTECT against challenge. An experimental subunit vaccine based on alpha-enolase protein elicited persistent antibody titers in piglets but PROVIDED LIMITED CLINICAL PROTECTION." Set against 53.5.6.1: oxytetracycline is the treatment of choice, and chlortetracycline fed to the sow herd for two weeks nearly abolished dysgalactia.
How this level was decided
Level 1 ON THE "NOT NEEDED" CLAUSE, NOT ON AVAILABILITY, and FLAGGED FOR ERIC AS A LEVEL 1 OR 3 JUDGMENT because those are the two candidates and they are at opposite ends of the criterion. There is certainly no vaccine: two experimental candidates have failed and the organism cannot even be cultured. So the whole question is the second half of the C8 test, whether the disease would justify vaccinating, which the 2026-08-28 rewording says to judge on the agent's own clinical and economic weight. THE CASE FOR LEVEL 1, which is scored: most infection is subclinical, C5 is scored level 2 on the same evidence, and an effective and cheap antimicrobial already controls the disease at herd level -- this is the Trichinella pattern Eric set, where there is no imperative to develop something because the problem is already handled. THE CASE FOR LEVEL 3 is that the control depends entirely on tetracyclines given to whole sow herds, which is exactly the kind of prophylactic group medication a vaccine would displace. THAT ARGUMENT CANNOT BE MADE INSIDE THIS FRAMEWORK, and it is worth saying so: antimicrobial use is scored nowhere in the 8 criteria after both AMR criteria were removed, so "a vaccine would replace herd-level tetracycline" has no cell to live in. Recorded here rather than left silent, as on the E. coli entries.
Levels and evidence are generated from data/assignments/mycoplasma_suis.yml; the overview is authored in data/overviews/mycoplasma_suis.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.