Yersinia pseudotuberculosis
LEVELS: Sometimes occurs; Mild; Routine biosecurity keeps it out; Laboratory-dependent; Minor; Negligible; Little; Available, or not needed
| Register id | yersinia_pseudotuberculosis |
| Type | bacteria |
| Scientific name | Yersinia pseudotuberculosis |
| NCBI taxid | 633 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Yersinia pseudotuberculosis is the minor partner to Y. enterocolitica on this register. It is found mainly in rodents and only uncommonly in pigs, and it accounts for less than one percent of human yersiniosis. Its potential to cause disease in pigs is real but rarely realised: experimentally, oral inoculation of ten-week-old pigs produced watery diarrhoea in a quarter of them and lesions of enterocolitis in half, and one survey found it as the sole isolate on four of 85 farms with confirmed enterocolitis in growing pigs — but that report is atypical, and pigs shedding it on commercial farms are generally healthy. The gross lesions of erosive ileitis are not specific and are also seen in salmonellosis, which is far more common, so diagnosis needs clinical signs, microscopic lesions and culture or PCR together; a positive culture alone proves little because subclinical shedding is common. Absent clinical disease, Yersinia infections in pigs are rarely treated or controlled, and there is no vaccine. Unlike Y. enterocolitica, it does not carry the O:9 antigen that interferes with brucellosis serology.
C1 Zoonotic potential
Likelihood of transmission from pigs to humans
Sometimes occurs: Known risk of transmission to humans (foodborne or occupational), but requires failure of one or more control points for transmission to humans
Basis. "The primary importance of Yersinia enterocolitica and, to a lesser extent, Yersinia pseudotuberculosis in swine is as a source for food-borne infection of humans that handle or consume contaminated pork products." "The vast majority of human yersiniosis is caused by Y. enterocolitica, with Y. pseudotuberculosis accounting for less than one percent." "Control of foodborne disease is best accomplished in the slaughter plant to reduce fecal contamination of carcasses and in the home with appropriate sanitation during food preparation and by cooking pork and pork products to appropriate core temperatures." (ch58 58.14.1, 58.14.3)
How this level was decided
The chapter names this species as a pork-borne source of human infection, lesser than Y. enterocolitica but the same route, and the same three control points govern it -- slaughter hygiene, kitchen sanitation, cooking. Level 3, which asks for a known risk released by a control point failure and says nothing about how often. Level 2 does not fit despite the rarity, because its second clause requires that no control point be directed at the route, and here the control points are the same ones the chapter specifies for pork generally.
C2 Zoonotic impact
Severity of human illness caused by the agent
Mild: Human illness is usually mild and self-limiting, and serious disease occurs only rarely
Basis. "Most human yersinosis cases manifest as self-limiting enterocolitis in children 5 years of age or younger that exhibit pyrexia, vomiting, and severe, often bloody diarrhea. Adults may experience similar signs, but more commonly acute ileitis and purulent mesenteric lymphadenitis result in acute abdominal pain along with vomiting and diarrhea that mimics acute appendicitis." (ch58 58.14.1)
How this level was decided
Corrected from level 3 on 2026-08-27, before review, for the same reason as yersinia_enterocolitica -- see that entry. Chapter 58 describes the human illness for the two species in one passage, so they move together. The mesenteric adenitis presentation that this species is classically associated with is the one the chapter says mimics appendicitis in adults, but it sits inside an illness the chapter calls self-limiting, which is level 2. NOTE: the criteria file names only Y. enterocolitica as the level 2 example, so this entry was not itself flagged by the cross-check; it is corrected for consistency with the passage both entries are scored from.
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
Basis. "In contrast, Y. pseudotuberculosis is most commonly found in rodents and uncommonly in pigs." "Yersinia enterocolitica can be isolated from a wide variety of mammals and birds... It can also be detected in the environment, including ponds and lakes." (ch58 58.14.2)
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. rodents and birds. Same programme, same level.
EARLIER REASONING, kept because it is the evidence read: RENUMBERED L4 -> L5 on 2026-09-01, when C3 went from four levels to five. The argument below is unchanged and so is the judgment. What changed is the scale it sits on. C3 now runs on the EFFORT REQUIRED TO EXCLUDE: L1 already in the herd, L2 housing alone keeps it out, L3 routine biosecurity keeps it out, L4 extraordinary biosecurity required, L5 exclusion may not be achievable. Cleaner than the level 4 on Y. enterocolitica, and for a different reason. This species is primarily a rodent organism that pigs pick up rather than a pig organism -- rodents are established everywhere US pigs are kept, outside the pig industry, and give continuous opportunity for exposure that no herd biosecurity closes. Level 4.
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. "l2, straightforward to diagnose"
Basis. "Diagnosis of porcine enteric yersiniosis requires the combination of clinical signs of diarrhea, typical microscopic lesions, and confirmation of infection by culture or PCR. Positive culture in diarrheic pigs is insufficient since subclinical shedding of Yersinia spp. is relatively common." "Gross lesions of erosive ileitis are nonspecific since they are also observed in cases of enteric salmonellosis (Chapter 55), which is a much more common disease in commercial swine." "Yersinia enterocolitica and Y. pseudotuberculosis can readily be isolated at 37 C on blood and MacConkey agar from tissues with lesions." (ch58 58.14.3)
How this level was decided
Lesions are explicitly non-specific against enteric salmonellosis, so the presentation does not point here -- not level 1. Isolation is routine blood and MacConkey agar work with cold enrichment, available regionally. Level 2.
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
Basis. "Neef and Lysons (1994) orally inoculated 10-week-old pigs with Y. pseudotuberculosis and produced watery diarrhea in 25% and gross or microscopic lesions of enterocolitis in 50%. This suggests the potential for clinically significant disease in a commercial setting and is consistent with the findings of Thomson et al. (1998), where Y. pseudotuberculosis was the sole isolate from pigs on 4 of 85 farms where enterocolitis and diarrheal disease were confirmed in 15-50 kg pigs. However, this report is atypical, and pigs shedding Y. pseudotuberculosis on commercial pig farms are generally without clinical disease." "their importance in enteric disease in commercial swine production is relatively minor." (ch58 58.14.1, 58.14.2)
How this level was decided
This species has a better claim to causing real disease than Y. enterocolitica does -- experimental infection produced diarrhoea in a quarter of pigs and lesions in half, and it was the sole isolate on four farms with confirmed enterocolitis. But the chapter calls that report atypical and says shedding pigs are generally healthy. Small and occasional losses rather than a standing cost, which is level 2. NOTE: the brucellosis serology cross-reaction that drives the cost on Y. enterocolitica belongs to serotype O:9 of that species and does not apply here.
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 is correct, the disease in pigs and the disease in humans is not strongly linked. the disease is not readily contagious between pigs and would be unlikley to cause outbreaks or have market effect"
Basis. This species accounts for less than one percent of human yersiniosis, causes little disease in pigs, and does not carry the serotype O:9 antibody that cross-reacts with brucellosis serology. The section records no trade measure, movement control, export restriction or consumer response attaching to it.
How this level was decided
INFERRED, and deliberately scored a level below yersinia_enterocolitica. Both routes that gave that entry a level 2 are absent here: the brucellosis false positive is specific to Y. enterocolitica serotype O:9, and at under one percent of human yersiniosis this species does not generate the foodborne outbreaks that move demand. Level 1.
C7 Treatment potential
Potential for treatment to improve outcomes
Little: Effective pathogen-directed treatment is available and works, or animals recover acceptably without it
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c7l1, infection in pigs is not generally accompanied by clinical disease so there is little imperative to treat"
Basis. "Absent clinical disease, Yersinia infections in swine are rarely treated, prevented, or otherwise controlled." "pigs shedding Y. pseudotuberculosis on commercial pig farms are generally without clinical disease." (ch58 58.14.2, 58.14.3)
How this level was decided
INFERRED. Pigs shedding this organism are generally healthy and are not treated, so the second clause of level 1 holds -- animals do acceptably without treatment. NOTE: this is a shade less clear-cut than the same call on Y. enterocolitica, because the Neef and Lysons work shows this species can produce enterocolitis in a quarter of inoculated pigs. If Eric reads that as a real commercial disease rather than an experimental one, there is an outcome a treatment could improve and this becomes level 2 or 3.
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. Eric, 2026-08-28: "both yersinia should go to c8l1." The reworded pass had already reached level 1 here, so this confirms the machine rather than overriding it, and it supersedes his 2026-08-27 correction to level 3, which was written when level 3 was the only place a missing vaccine could go. Under 1% of human yersiniosis, most commonly a rodent organism, and little disease in pigs -- no vaccine is warranted.
Basis. ch58 58.14.3: "Presently there is insufficient data on how to reduce the prevalence of Yersinia spp. on infected farms", and no vaccine is named. The species accounts for "less than one percent" of human yersiniosis and is most commonly found in rodents.
How this level was decided
MOVED L3 -> L1 by the rewording. INFERRED, AND THIS SPLITS A SINGLE RULING OF ERIC'S -- see the note on yersinia_enterocolitica, which stays at level 3. He wrote one comment covering both species: "vaccinating pigs to reduce human disease is novel concept, but we are light years away". The reworded criterion asks whether a vaccine would be JUSTIFIED, which separates them: this species causes little pig disease and under 1% of human yersiniosis, so the answer is no. FLAGGED for his ruling.
Levels and evidence are generated from data/assignments/yersinia_pseudotuberculosis.yml; the overview is authored in data/overviews/yersinia_pseudotuberculosis.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.