Cutaneous Spirochetosis / Ear Necrosis
LEVELS: Highly unlikely; No human illness; Already in the herd; Reference or research laboratory required; Negligible; Negligible; Little; Available, or not needed
| Register id | treponema_pedis |
| Type | bacteria |
| Scientific name | Treponema pedis |
| NCBI taxid | 409322 |
| Evidence | 3 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Treponema pedis is the spirochaete found in porcine ear necrosis and skin ulcers, a condition of pigs shortly after weaning that is chiefly an animal welfare concern. The organism is consistently the predominant Treponema in these lesions, and oral treponemes transferred by biting and licking are the suspected source — it has been found in the gingiva of affected pigs. But causation is not established, and this register deliberately holds the paper that failed: inoculating pigs with T. pedis did not reproduce ear necrosis, and the aetiology of the syndrome remains unknown. Morbidity is usually low and affected pigs do not perform measurably differently from unaffected ones; lesions heal leaving a scar. Distinguishing the condition from bite wounds is difficult, and Staphylococcus hyicus is present in some lesions. Treatment of individual pigs with parenteral antimicrobials is possible but rarely done because the condition does not warrant it, and control is a matter of husbandry and enrichment. It has no known public health significance.
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. ch58 58.11.1: "T. pedis has no known public health significance." Neither Karlsson paper reports human infection, and neither addresses public health at all -- both are studies of the porcine lesion.
How this level was decided
Level 1 unchanged. Stated directly in the chapter and undisturbed by two new papers that had no occasion to contradict it.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
Basis. ch58 58.11.1: "T. pedis has no known public health significance."
How this level was decided
Level 1 unchanged. C2 says to score level 1 whenever the agent does not cause disease in people.
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. Karlsson 2017: "Oral treponemes have been suggested as source of infection, transferred by biting and licking behavior." "The number of Treponema-positive gingival samples increased during the study" -- including in the control pigs, which developed a weak IgG response "possibly caused by the oral treponemes". ch58 58.11.2: Pringle et al. "found the organism in the gingiva of affected pigs."
How this level was decided
Level 1 unchanged, and better supported than before. The 2017 study found treponeme colonisation of the gingiva rising across the study in control pigs that were never inoculated -- the organism was already in the pens and spreading between pigs by mouth. There is no introduction event to prevent. NOTE: this weakens the C3 escalation question here specifically. The old note flagged cattle and sheep digital dermatitis as a possible outside reservoir; the new evidence says pigs carry it orally among themselves, so the pig-to-pig account now stands on direct observation rather than on the chapter's inference.
C4 Detection difficulty
Difficulty of recognizing and confirming infection
Reference or research laboratory required: A validated assay exists, but only at a national reference or research laboratory rather than at local or regional level
Corrected by Eric from L2 Laboratory-dependent. Reason: "l3, lesion is very characteristic but not all local/regional labs could confirm the agent is present without referral"
Basis. Karlsson 2014 identified T. pedis as the predominant Treponema in porcine skin ulcers using fluorescence in situ hybridization and high-throughput sequencing. ch58 58.11.3: "A preliminary identification can be made microscopically in tissue sections utilizing silver stains." "The organisms can also be detected by using a PCR for treponemes." "Ear necrosis and localized necrotic lesions elsewhere on the body are suggestive of infection by T. pedis, but S. hyicus may be present in some lesions... Bite wounds are much more difficult to differentiate."
How this level was decided
Level 2 unchanged. The lesion is suggestive but confounded by bite wounds and S. hyicus, so level 1 is out; silver-stained histopathology and treponeme PCR are regional laboratory work. NOTE: the 2014 paper used FISH and high-throughput sequencing to establish which Treponema species predominates, which is research-grade work -- but that was answering a research question, not making a diagnosis, and species-level identification is not what a practitioner needs here.
C5 Production cost
Financial impact on the infected farm's cost of production
Negligible: No measurable effect on cost of production
Basis. ch58 58.11.3: "Morbidity is usually low, and affected pigs do not perform significantly differently from unaffected controls (Busch et al. 2010)." Karlsson 2017 abstract: "Ear necrosis is a syndrome affecting pigs shortly after weaning and is regarded as an animal welfare issue." Its five inoculated pigs "did not develop any clinical signs of infection".
How this level was decided
Level 1 unchanged. A controlled comparison found no performance difference, and the 2017 paper frames ear necrosis as a welfare issue rather than a production-cost one -- the same answer from a different direction. NOTE, as before: this records the production economics, not the welfare significance, and the framework has no criterion that carries welfare.
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
Basis. Neither new paper reports any trade measure, movement control, export restriction or consumer response. Both treat ear necrosis as an on-farm welfare and husbandry problem. ch58 records the condition in pigs "from most parts of the world".
How this level was decided
Level 1, and now supported rather than inferred -- Eric had asked for this cell to be re-assessed rather than ruling on it. A skin condition of no public health significance, with no measured performance effect, present worldwide, and not reportable, has no route to pork supply or demand.
C7 Treatment potential
Potential for treatment to improve outcomes
Little: Effective pathogen-directed treatment is available and works, or animals recover acceptably without it
Basis. ch58 58.11.4: "Treatment of individual pigs is possible using parenteral antimicrobials but is rarely carried out as the condition does not warrant it. Topical lincomycin-spectinomycin combinations have been used in cattle to treat T. pedis." ch58 58.11.3: "On resolution, they heal leaving a scar." Karlsson 2017 conclusion: "In the presented model T. pedis T A4 failed to cause skin lesions similar to those of ear necrosis."
How this level was decided
Level 1 unchanged, and the 2017 paper adds a reason that did not exist before. Treatment is available and lesions heal on their own, which was already both clauses of level 1. The new paper adds that pathogen-directed treatment aimed at T. pedis may be aiming at the wrong target: inoculating the organism did not produce the disease.
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
Basis. ch58 58.11.4 names antimicrobials, disinfection, enrichment and aldehydes, and no vaccine. ch58 58.11.3: affected pigs "do not perform significantly differently from unaffected controls". Karlsson 2017: the etiology of ear necrosis "is unknown" and inoculation of T. pedis failed to reproduce it.
How this level was decided
MOVED L3 -> L1 by the rewording, and this was the sharpest example of why the rewording was needed. The old level 3 scored maximum vaccine concern for an agent that produces no measurable production loss and that a controlled experiment failed to show causes the disease it is registered for. There is no justified target here. Level 1.
Levels and evidence are generated from data/assignments/treponema_pedis.yml; the overview is authored in data/overviews/treponema_pedis.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.