Brachyspira hampsonii (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_hampsonii |
| Type | bacteria |
| Scientific name | Brachyspira hampsonii |
| NCBI taxid | 1287055 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Brachyspira hampsonii is an anaerobic spirochaete that causes swine dysentery — a mucohaemorrhagic diarrhoea of grower and finisher pigs that is clinically and pathologically indistinguishable from the disease caused by its better-known relative B. hyodysenteriae. It was recognised in North America around 2007 and has since turned up in Europe. It is now the Brachyspira species most often isolated from dysentery cases in Canada and accounts for 15–25% of cases in the United States. Its most striking epidemiological feature is the reservoir: migratory waterfowl in both North America and Europe carry it, and an isolate of bird origin has produced the disease experimentally in pigs — so an outdoor herd can acquire it without any contact with another pig unit. It is distinguished from B. hyodysenteriae in the laboratory rather than in the pen, by being indole-negative and by molecular typing, and it appears rather more susceptible to the antimicrobials commonly used against dysentery.
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, routine biosecurity should definitely include use of quarantine for incoming stock. So L2 takes care of most of the risk but there can also be asymptomatic carriers and this needs managed through comprehensive quarantine and testing of new stock" HIS QUARANTINE POINT IS THE REASON THESE FOUR SIT AT LEVEL 3 RATHER THAN LEVEL 2. Housing closes the waterfowl route, but asymptomatic carriers arrive in incoming stock, and finding them needs quarantine and testing -- which is the level 3 list. EARLIER RULING, 2026-09-02, kept because a later decision does not erase the reasoning it replaced: CONFIRMED. "c3l5, agree with assessment" 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: "Waterfowl appear to be a significant reservoir and potential means of introduction and spread for B. hampsonii, as this agent has been recovered from migratory waterfowl samples in North America and Europe, and an avian-origin isolate of B. hampsonii induced SD in experimentally inoculated pigs." "B. hampsonii continues to be the Brachyspira spp. that is most frequently isolated from cases of SD in Canada, while it is associated with 15-25% of cases in the United States." 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. Eric, 2026-09-03: "who cares about waterfowl reservoirs? Moving pigs indoors largely solves the issue." It goes to level 3 rather than level 2 because the PRIMARY route into a herd is an introduced pig and housing does nothing about a pig arriving in a truck. Level 3 is where B. hyodysenteriae already sits as the worked example, and these are the same disease.
EARLIER REASONING, kept because it is the evidence read: Level 5, and it is a genuine two-level split from brachyspira_hyodysenteriae in the same chapter and the same disease. The chapter calls migratory waterfowl a SIGNIFICANT RESERVOIR for this species, the organism has been recovered from waterfowl in North America itself rather than only abroad, and an avian isolate reproduced swine dysentery in pigs -- so the reservoir is not merely present, it is proven competent. Migratory waterfowl sit outside the farm and outside the industry, they are already here, and nobody removes them. Note that the species is not exotic either: it is already the commonest SD agent in Canada and 15 to 25% of US cases. FLAGGED so the divergence is visible: B. hyodysenteriae is scored level 3 because its rodents and birds are mechanical carriers between infected farms, while this species has a wildlife maintenance host.
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, agree with assessment"
Basis. ch45 45.1.1: "Complications arose when two other strongly beta-hemolytic species (Brachyspira hampsonii and Brachyspira suanatina) were shown to cause a disease indistinguishable from SD. This means that caution is required where reliance is placed on diagnostic methods that only detect B. hyodysenteriae in cases of SD." 45.2.8: "some avian strains of B. hampsonii may cross-react in these B. hyodysenteriae PCRs and PCRs for other Brachyspira species." "B. hampsonii is usually identified using a nox-based PCR", and MALDI-TOF "can discriminate the known agents of SD".
How this level was decided
Level 2, one level above brachyspira_hyodysenteriae and for a reason the chapter puts in its opening summary. The clinical picture is not the problem: the disease is indistinguishable from swine dysentery, so dysentery is suspected in normal practice exactly as it is for B. hyodysenteriae. The problem is that the routine workup is DIRECTED at the wrong species -- a laboratory running a B. hyodysenteriae-specific PCR returns a negative on a pig that has swine dysentery, and some avian B. hampsonii strains cross-react in those assays and mislead in the other direction. Confirming the species needs a nox-based PCR or MALDI-TOF, which regional laboratories do run, so this is level 2 rather than 3. FLAGGED as a level 1 or 2 judgment: if the entry is read as swine dysentery rather than as this species, the clinical route is open and it is level 1 with the sister entry.
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
Basis. ch45 45.1.1 and 45.2.1: B. hampsonii causes "a disease indistinguishable from SD", and SD as a whole "causes considerable financial loss due to mortality, slow growth rates, poor feed conversion, and costs of treatment". 45.2.4: "B. hampsonii continues to be the Brachyspira spp. that is most frequently isolated from cases of SD in Canada, while it is associated with 15-25% of cases in the United States."
How this level was decided
Level 3, scored the same as brachyspira_hyodysenteriae because the chapter says the disease it causes cannot be told apart from the disease that species causes. This is not an exotic or theoretical entry: it is already the leading cause of swine dysentery in Canada and up to a quarter of US cases, so the cost is being paid now. Losses that measurably increase cost of production and are managed within normal farm operations.
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 evidence to suggest market is or would react to a diagnosis"
Basis. Section 45.2 records no trade measure, movement control or consumer response. B. hampsonii has been present in North American pigs since around 2007 and is the commonest SD agent in Canada.
How this level was decided
INFERRED. Under the standing note SCORING/market_impact, an agent present in US and Canadian pigs for nearly two decades and routinely diagnosed, with no market move on record, scores 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
Corrected by Eric from L1 Little. Reason: MOVED L1 -> L2, reversing the assessment. 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. Being more susceptible to tiamulin than the species on the label does not put B. hampsonii on the label. Treating it is extralabel, which is level 2. This matters practically as well as formally, because B. hampsonii is already the commonest agent of swine dysentery in Canada and 15-25% of US cases, so a large and growing share of the disease is being treated off-label.
Basis. ch45 45.2.10.1: "In the United States, isolates of the recently emerged B. hampsonii have been reported to be more susceptible to tested antimicrobials than isolates of B. hyodysenteriae (Hakimi et al. 2024)." "In pigs experimentally infected with susceptible isolates of either B. hyodysenteriae or B. hampsonii, water medication with tiamulin resolved clinical disease within 24 hours and eliminated viable spirochete shedding within 72 hours."
How this level was decided
Level 1, and this is a DELIBERATE SPLIT from brachyspira_hyodysenteriae at level 2, made on an explicit statement rather than an inference. Tiamulin is labelled for swine dysentery in the US, it cleared clinical disease in 24 hours and shedding in 72 in experimentally infected pigs, and a 2024 US survey found this species MORE susceptible than B. hyodysenteriae. Under the standing note SCORING/treatment_potential that is a labelled product that works and is used, which is level 1. FLAGGED because the whole genus is trending toward multidrug resistance and this reading depends on a single recent susceptibility comparison holding.
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
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." The commercial bacterins the chapter describes are B. hyodysenteriae products, and no vaccine of any kind for B. hampsonii is named. 45.2.4: it is the commonest SD agent in Canada and 15-25% of US cases.
How this level was decided
Level 3, and a deliberate split from brachyspira_hyodysenteriae at level 2. No vaccine exists for this species anywhere -- the chapter treats its emergence as a problem FOR vaccination rather than something vaccination addresses -- and the disease plainly justifies one, being the leading cause of swine dysentery in Canada and a quarter of US cases. Needed but not available, which is the level 3 definition. The target is also demonstrably tractable, since bacterins against the sister species give at least a degree of protection.
Levels and evidence are generated from data/assignments/brachyspira_hampsonii.yml; the overview is authored in data/overviews/brachyspira_hampsonii.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.