Yersinia enterocolitica
LEVELS: Sometimes occurs; Mild; Routine biosecurity keeps it out; Laboratory-dependent; Minor; Temporary disruption; Little; Available, or not needed
| Register id | yersinia_enterocolitica |
| Type | bacteria |
| Scientific name | Yersinia enterocolitica |
| NCBI taxid | 630 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Yersinia enterocolitica matters in pigs almost entirely because of people. Most infections in swine are silent and it is a minor cause of enteric disease in commercial production, but the pig is the primary reservoir for human yersiniosis and around 75% of human cases are attributed to preparing or eating raw or undercooked pork. The same serotypes and genotypes predominate on both sides. Pigs carry it in the tonsils and intestine and shed it in faeces; it also occurs in ponds and surface water. Buying pigs from outside sources, feeding animal protein products and using surface or shallow-well water all raise the risk of a farm becoming infected. One further consequence is worth knowing because it costs money without any pig being ill: antibody to serotype O:9 cross-reacts in brucellosis serology, producing false-positive swine brucellosis results that can trigger quarantine and extensive confirmatory testing.
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... in swine is as a source for food-borne infection of humans that handle or consume contaminated pork products. Swine are the primary carrier of Y. enterocolitica and source for human yersiniosis." "Approximately 75% of human yersiniosis is attributed to the preparation or consumption of contaminated raw or undercooked pork." "Predictably, the same serotypes and genotypes predominate in swine and human infections." "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
This is the same shape as Salmonella, which Eric ruled level 3, and it is if anything cleaner. The pig is named as the primary reservoir and the source of human yersiniosis, the route is pork, three-quarters of human cases are attributed to it, and matching genotypes close the chain. The chapter then names the control points exactly -- slaughter hygiene to limit faecal contamination of carcasses, kitchen sanitation, and cooking to core temperature -- so transmission follows their failure. Level 3.
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." "Yersiniosis has been the third to fourth most frequent zoonosis in the European Union from 2004 to 2011." (ch58 58.14.1)
How this level was decided
Corrected from level 3 on 2026-08-27, before review, by the criteria cross-check in validate_criteria.py -- C2 level 2 names Yersinia enterocolitica as a worked example and the assignment said level 3. On re-reading, the example is right and the first pass was wrong. The chapter's own characterisation leads with the operative word: most cases are "self-limiting enterocolitis". Level 3 requires that clinically important illness be common and commonly need medical treatment or hospitalisation, and the folder does not say that. What misled the first pass was "severe, often bloody diarrhea" and the appendicitis mimicry, but level 2 expressly accommodates those -- it reads "usually mild and self-limiting, and serious disease occurs only rarely". The framework's calibration is also deliberate and worth preserving: it places Campylobacter at level 3 and Yersinia at level 2, and the folder supports exactly that distinction, because chapter 58 names Guillain-Barre syndrome and reactive arthritis as Campylobacter sequelae and names no sequelae at all for Yersinia.
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. "Yersinia enterocolitica can be isolated from a wide variety of mammals and birds, with the pig being the primary reservoir. It can also be detected in the environment, including ponds and lakes (Greenwood et al. 1990)." "Factors known to increase the risk for farm infection are the purchase of swine from outside sources, feeding of animal protein products, and use of surface or shallow-well water sources (Virtanen et al. 2014; Wesley et al. 2008)." "studies have indicated 32-53% of US farms... are infected." (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, birds and water. 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. Three of the routes the chapter names are outside the pig industry: a wide range of wild mammals and birds, surface water and shallow wells, and feed. Purchasing pigs is closable by biosecurity, but water and wildlife are not, and C3 says the least reachable reservoir governs. Level 4. That 32-53% of US farms are already infected reinforces rather than changes the answer.
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. "Enteropathogenic Y. enterocolitica and Y. pseudotuberculosis do not generally cause clinical disease in pigs on commercial swine farms." "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." "Positive culture in diarrheic pigs is insufficient since subclinical shedding of Yersinia spp. is relatively common, and there are a large number of other causes of diarrhea in swine." "Yersinia enterocolitica and Y. pseudotuberculosis can readily be isolated at 37 C on blood and MacConkey agar from tissues with lesions. Most isolation methods for Yersinia use cold enrichment techniques." (ch58 58.14.2, 58.14.3)
How this level was decided
There is usually no clinical disease at all, and where lesions occur they are indistinguishable from the far commoner enteric salmonellosis -- so nothing points at this agent, ruling out level 1. Isolation is blood and MacConkey agar with cold enrichment, standard regional laboratory work. Level 2. The interpretive trap the chapter flags -- that a positive culture proves nothing because subclinical shedding is common -- is a confounder, not a referral requirement.
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. "Most infections by Y. enterocolitica and Y. pseudotuberculosis in swine are asymptomatic, and their importance in enteric disease in commercial swine production is relatively minor." "Of additional significance, antibody to Y. enterocolitica serotype O:9 cross-reacts in serological tests for Brucella spp., causing false positive results for swine brucellosis, which in turn can instigate costly quarantines and extensive confirmatory diagnostic testing (Free et al. 2020)." "Inoculation of 11- to 24-week-old pigs with Y. enterocolitica resulted in colonization and fecal shedding, but no clinical disease was observed." (ch58 58.14.1, 58.14.2)
How this level was decided
The disease itself costs almost nothing -- the chapter calls its importance in commercial production relatively minor and infection generally asymptomatic. The farm cost that does exist is unusual and worth Eric seeing: serotype O:9 antibody cross-reacts with the brucellosis serology, and the chapter says the false positives instigate costly quarantines and extensive confirmatory testing. Small and episodic rather than a standing increase in cost of production, so level 2 rather than level 3.
C6 Market impact
Duration of material disruption to pork and pig markets
Temporary disruption: Material negative effect on supply or demand lasting less than a month 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. "I think C6L2 is correct, the disease is transmissible and foodborne outbreaks have been attributed back to pigs, and human cases of pig attributed cases are rising."
Basis. "antibody to Y. enterocolitica serotype O:9 cross-reacts in serological tests for Brucella spp., causing false positive results for swine brucellosis, which in turn can instigate costly quarantines and extensive confirmatory diagnostic testing." "Yersiniosis has been the third to fourth most frequent zoonosis in the European Union from 2004 to 2011... is overrepresented as a regional and seasonal disease associated with the preparation or consumption of chitterlings." (ch58 58.14.1)
How this level was decided
INFERRED. Two routes to a market effect, both short. A brucellosis false positive puts the herd under quarantine until confirmatory testing clears it, which is a genuine movement restriction lasting weeks. A pork-linked human outbreak brings product withdrawal and a local demand effect over a similar span. Neither closes export markets or moves national supply. Material effect lasting less than a month is level 2. NOTE: this is the only entry in the ch58 batch scored above level 1 on C6 without a regulatory disease behind it, and it is the brucellosis cross-reaction rather than the yersiniosis that does the work.
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 is correct. Pigs are generally an asymnptomatic carrier and therefore there is not a clinical demand to treat. Treatmetn to reduce likelihood of onward human infection is creative idea, has been discussed, but never implemented."
Basis. "Absent clinical disease, Yersinia infections in swine are rarely treated, prevented, or otherwise controlled." "Enteropathogenic Y. enterocolitica and Y. pseudotuberculosis do not generally cause clinical disease in pigs on commercial swine farms." "colonization by Y. enterocolitica in a commercial setting is most common in 2- to 5-month-old pigs, but clinical disease is not generally observed." (ch58 58.14.2, 58.14.3)
How this level was decided
INFERRED. C7 scores how much better the pig outcome would be with a treatment, and there is no adverse pig outcome to improve -- colonisation is the norm and disease is not. The second clause of level 1 is satisfied: animals do acceptably without treatment. Same reasoning as campylobacter_spp in this batch. NOTE: treating pigs to cut human exposure is a food safety intervention, not a pathogen-directed treatment improving the pig outcome, so it does not lift this level -- and the chapter puts that control in the slaughter plant and the kitchen anyway.
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
Corrected by Eric from L3 Needed but not available. Reason: Eric, 2026-08-28: "both yersinia should go to c8l1." This overturns my split. Under the reworded C8 I kept this entry at level 3 and moved Y. pseudotuberculosis to level 1, arguing that his earlier "light years away" comment was about FEASIBILITY while the new level 3 asks about JUSTIFICATION, and that a vaccine removing three quarters of human yersiniosis would be justified however distant. He has ruled the other way, and the ruling is his to make: the justification test is whether the disease warrants vaccinating PIGS, and pigs are asymptomatic carriers. A vaccine given to pigs purely to reduce human foodborne illness is a food safety intervention, and the control point for that already sits in the slaughter plant and the kitchen, which is where ch58 puts it. His original comment stands unchanged in substance -- only the level it now maps to has moved, because level 3 is no longer the only place a missing vaccine can go.
Basis. ch58 58.14.1: swine are "the primary carrier of Y. enterocolitica and source for human yersiniosis", and "approximately 75% of human yersiniosis is attributed to the preparation or consumption of contaminated raw or undercooked pork". No vaccine is named anywhere in 58.14.
How this level was decided
STAYS L3 under the rewording, deliberately parting from yersinia_pseudotuberculosis, which moves to level 1. Eric's single comment covered both -- "we are light years away from adopting this approach or even knowing if it would work" -- but that is a statement about FEASIBILITY, and the reworded level 3 asks about JUSTIFICATION. A pig vaccine that cut carriage would remove three quarters of human yersiniosis, which is a justified unmet need however distant the technology. FLAGGED: his ruling was written when level 3 was the only place a missing vaccine could go, so it needs re-confirming either way.
Levels and evidence are generated from data/assignments/yersinia_enterocolitica.yml; the overview is authored in data/overviews/yersinia_enterocolitica.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.