Brachyspira suanatina (swine dysentery)
LEVELS: Highly unlikely; No human illness; Routine biosecurity keeps it out; Laboratory-dependent; Moderate; Negligible; Some; Needed but not available
| Register id | brachyspira_suanatina |
| Type | bacteria |
| Scientific name | Brachyspira suanatina |
| NCBI taxid | 381802 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Brachyspira suanatina is one of three strongly beta-haemolytic Brachyspira species that cause swine dysentery, and it produces a disease indistinguishable from the classical one caused by B. hyodysenteriae — mucohaemorrhagic diarrhoea in growing pigs with the mortality, slow growth, poor feed conversion and treatment costs that go with it. It was first identified in the early 2000s and so far has been isolated only rarely, from pigs in Scandinavia and Germany. It is on this register because it is not present in the United States and the US imports breeding stock from Scandinavia, which makes it an emerging introduction risk rather than a current problem. Two features complicate control. It has been recovered from waterfowl in Sweden and Denmark, and pigs given a bird-origin isolate developed dysentery, so outdoor herds can acquire it without contact with other pigs. And a laboratory that tests only for B. hyodysenteriae will miss it — detection requires selective culture, MALDI-TOF speciation, or the specific rpoC PCR. None of the agents of swine dysentery is known to infect people.
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. ch45 45.2.3, the whole of the public health section for swine dysentery and covering all three of its agents: "None of the agents of SD are known to infect humans."
How this level was decided
Level 1, stated outright for all three agents of swine dysentery.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
Basis. ch45 45.2.3, the whole of the public health section for swine dysentery and covering all three of its agents: "None of the agents of SD are known to infect humans."
How this level was decided
Level 1. The chapter says none of the agents of SD infects people.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED at level 3 on the C3 review sheet. "l3, as above for B.hyo" EARLIER RULING, 2026-09-02, kept because a later decision does not erase the reasoning it replaced: CONFIRMED. "c3l5, organism seems to be essentially the same type of agent as B. hampsonii so should be scored the same on this criteria" RESCALED 2026-09-03, when C3 went from five levels to four and level 4 absorbed level 5. A ruling of his is never overturned by a scale change, so what is recorded here is the same judgment expressed on the new scale. AND THE ENTRY ALSO MOVED, on the pass Eric approved the same day: the whole old level 5 block was re-read against the exclusion test rather than the reservoir test, because twenty-one of those entries had been renumbered past the housing level on 2026-09-01 without being judged against it. See the entry justification for the reason this one moved. Recorded on the old scale as level 5, from_level 5.
Basis. ch45 45.2.4: "Similarly, B. suanatina has been recovered from waterfowl in Sweden and Denmark, and pigs inoculated with an avian-origin isolate developed clinical signs of SD." "B. suanatina was first identified in the early 2000s, and to date, it has only been isolated rarely from pigs in Scandinavia and Germany." 45.2.10.1: "it is virtually impossible to prevent mechanical transmission of infectious material via birds, waterfowl, insects, and other potential wildlife vectors in outdoor facilities."
How this level was decided
MOVED L5 -> L3 on 2026-09-03, when C3 was reduced to four levels and the whole level 5 block was re-read against the exclusion test rather than the reservoir test. Eric: "C3 is about exclusion, not reservoirs per se, though the two are related", and "who cares about reservoirs? Reservoirs really don't matter as long as you keep domestic pigs from becoming infected through biosecurity implementation." THE PREVIOUS LEVEL WAS NEVER JUDGED: this entry carried a RENUMBERED L4 -> L5 stamp from 2026-09-01, meaning it was moved past the newly created housing level rather than assessed against it. with hampsonii and pilosicoli, and for the same reason.
EARLIER REASONING, kept because it is the evidence read: INFERRED, AND FLAGGED AS THE WEAKER OF THE TWO WATERFOWL CASES IN THIS BATCH. The mechanism is the same as brachyspira_hampsonii and it is demonstrated to the same standard -- recovery from waterfowl, and an avian-origin isolate reproducing swine dysentery in inoculated pigs -- so if the agent arrived here it would have a wildlife maintenance host and nobody could remove it. What is NOT on the page is the North American half: B. hampsonii has been recovered from migratory waterfowl in North America itself, while B. suanatina has only been found in Swedish and Danish waterfowl. Scored level 5 because the birds are migratory and of the same orders, and because the level 5 test asks whether a reservoir exists OR WOULD ESTABLISH after an incursion. If Eric judges that a Scandinavian demonstration does not establish North American competence, this becomes level 3 on the Hendra pattern.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c4l2, organism seems to be essentially the same type of agent as B. hampsonii so should be scored the same on this criteria, the relevant work on the agent from Europe is credible"
Basis. ch45 45.1.1: B. suanatina causes "a disease indistinguishable from SD", and "caution is required where reliance is placed on diagnostic methods that only detect B. hyodysenteriae in cases of SD." 45.2.8: "PCRs based on the tlyA and rpoC genes have been described for B. hampsonii and B. suanatina, respectively." MALDI-TOF is "a rapid methodology for Brachyspira speciation that can discriminate the known agents of SD" and "is becoming standard practice in veterinary diagnostic laboratories". Selective anaerobic culture "has the capacity to detect all known agents of SD and provides a hemolytic phenotype".
How this level was decided
INFERRED, and scored the same as brachyspira_hampsonii for the same reason: the disease is recognised clinically but the species is missed by a workup aimed at B. hyodysenteriae. Culture catches it as a strongly haemolytic SD agent whatever the species, and MALDI-TOF is described as discriminating the known agents of SD, which this is. Level 2. FLAGGED as a level 2 or 3 judgment: the rpoC PCR is a research description rather than a service, and it is not certain a US laboratory's MALDI-TOF reference database contains a species that has never been isolated on this continent.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c5l3, organism seems to be essentially the same type of agent as B. hampsonii so should be scored the same on this criteria"
Basis. ch45 45.1.1: B. suanatina was "shown to cause a disease indistinguishable from SD". 45.2.1: SD "causes considerable financial loss due to mortality, slow growth rates, poor feed conversion, and costs of treatment". Against that, 45.2.4: "to date, it has only been isolated rarely from pigs in Scandinavia and Germany".
How this level was decided
INFERRED. C5 asks what the disease costs when it occurs, not how often it occurs, and what this agent causes is swine dysentery -- the chapter says the two cannot be told apart. So it is scored level 3 with the other two SD agents. FLAGGED: this entry is exotic to the US and rare even where it exists, so if Eric prefers C5 to carry frequency as well as severity it drops to level 2. The rarity is already carried elsewhere in the model, at C3 and C6.
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, incursion into the US could be either pig borne or waterfowl borne but in any case, seems unlikely a diagnosis would impact the market"
Basis. Section 45.2 records no trade measure, movement control or consumer response. B. suanatina has been recognised in pigs in Scandinavia and Germany since the early 2000s and swine dysentery is not a WOAH-listed disease.
How this level was decided
INFERRED, and it passes the precedent test added to SCORING/market_impact on 2026-09-02 rather than being inferred from nothing. The agent is exotic to the US, but something HAS been observed elsewhere: it has been causing swine dysentery in Scandinavian and German pigs for twenty years inside the European Union without a market consequence anyone recorded. That is an observed precedent of no reaction, which is what makes this scoreable. 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 at level 2, and this is the cell his ruling was written on. His ruling of 2026-09-02, made on the suanatina C7 cell and explicitly directed at all three agents of swine dysentery: "c7l2, check your work on hampsonii and hyodysenteriae. The US tiamulin label says \"For control of porcine proliferative enteropathies (ileitis) associated with Lawsonia intracellularis and for control of swine dysentery associated with Brachyspira (formerly Serpulina or Treponema) hyodysenteriae susceptible to Tiamulin.\" In other words, for this criteria B.hyo should be C7L1, but hampsonii and suanatina would be extralabel C7L2 by my reading." THE TEST IS THE LABEL TEXT, NOT THE SUSCEPTIBILITY. The assessment had scored these two cells the other way round, putting B. hampsonii at level 1 because a 2024 US survey found it MORE susceptible to tiamulin than B. hyodysenteriae. That is the wrong question. The standing note SCORING/treatment_potential says level 1 is where a labelled product already works and is used, and level 2 where treatment requires extralabel use -- and the label names one species. The assessment had reached level 2 here by a different route -- inferring from the genus because the chapter gives no suanatina-specific susceptibility data -- and arrived at the right answer for a weaker reason. The label settles it: this species is not named, so treating it is extralabel.
Basis. Chapter 45 gives no treatment data specific to B. suanatina. 45.2.10.1 covers treatment for the agents of SD as a group -- pleuromutilins and lincomycin, with the warning that "only a few effective antimicrobials remain available for treatment" and that MIC determination should precede treatment.
How this level was decided
INFERRED from the group rather than from anything specific to this species, and scored with brachyspira_hyodysenteriae at level 2 rather than with brachyspira_hampsonii at level 1. The reason for that choice is the absence of evidence rather than its presence: the chapter reports a 2024 US survey finding B. hampsonii MORE susceptible than B. hyodysenteriae, and says nothing at all about B. suanatina, so there is no basis to assume it is the easy one. Treatment exists but is inconsistent. FLAGGED as inferred.
C8 Vaccine availability
Availability of effective vaccines or bacterins
Needed but not available: No effective vaccine is available in the US or has been developed, and the disease would justify vaccinating if one existed
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c8l3, given the prevalence of clinical disease in US is low for all 3 SD agents, there is not a lot of market imperative to develop a vaccine but given AMR pressure, seems like there could be some reason to develop vaccine given we now have 3 agents causing the same disease"
Basis. ch45 45.2.10.1: "The emergence of B. hampsonii and B. suanatina further complicates the vaccination issue for SD, as commercial vaccines would likely need to protect against at least two of these agents depending on the geographic market." No vaccine for B. suanatina is described anywhere in the chapter.
How this level was decided
INFERRED, and scored with brachyspira_hampsonii at level 3. No vaccine exists for this species, the chapter names its emergence as a complication FOR vaccination, and the disease it causes is swine dysentery, which plainly justifies vaccinating. Needed but not available. FLAGGED, and this is the same rarity question as C5: the agent has only ever been isolated rarely from pigs in two regions, and if Eric weighs that this becomes level 1 on the ground that the disease does not justify a product nobody would buy.
Levels and evidence are generated from data/assignments/brachyspira_suanatina.yml; the overview is authored in data/overviews/brachyspira_suanatina.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.