Escherichia coli (postweaning colibacillosis)
LEVELS: Highly unlikely; No human illness; Already in the herd; Routine; Minor; Negligible; Little; Needed but not available
| Register id | ecoli_postweaning_diarrhea |
| Type | bacteria |
| Scientific name | Escherichia coli |
| NCBI taxid | 562 |
| Evidence | 2 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Postweaning diarrhoea is caused by enterotoxigenic Escherichia coli, most often strains carrying the F18 fimbria, and it appears in the first three weeks after weaning. The timing is not accidental: the gut receptor F18 strains need is barely present in the suckling pig and becomes strongly expressed from about three weeks of age, just as maternal antibody in milk is withdrawn and the pig is moved, mixed and put onto solid feed. Affected pigs pass watery yellow-grey diarrhoea with a characteristic smell for about a week. Sudden deaths occur, particularly at the start of an outbreak, and mortality can reach 25%. A related group, enteropathogenic E. coli, leaves survivors stunted and thriftless. Carriage in normal pigs is high — two-thirds of nursery pigs shed ETEC without being ill — so control turns on feed, water, hygiene and weaning management rather than on keeping the organism out. It is among the most expensive routine diseases in the nursery, put at roughly $179 per sow for a low-grade problem.
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. ch49 49.3, the whole public health section for the chapter, and it is about ONE pathotype: "A STEC subgroup known as EHEC, particularly EHEC O157:H7, O26, and other non-O157 serogroups, may be sporadically present in the intestines and feces of pigs and are known to cause bloody diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome in humans infected through food or water contaminated by animal feces. PIGS ARE NOT CONSIDERED A MAJOR SOURCE OF O157 EHEC, AS THE PREVALENCE RATE IS TYPICALLY VERY LOW." Surveys of healthy slaughter pigs: Alberta 1.4%, Japan 1.4%, Ireland 0.21-0.63%, UK 0.3%, Sweden 0.08%, Norway 0.1%, United States 2%.
How this level was decided
Level 1, on the same structured silence as the neonatal entry. Postweaning colibacillosis is caused by ETEC carrying F4 and F18 fimbriae and by EPEC, and the chapter's public health section discusses neither -- it discusses EHEC, a different pathotype that this entry is not. F4 and F18 are porcine colonisation factors binding receptors on pig enterocytes. NOTE, A FRAMEWORK GAP RATHER THAN AN ENTRY ONE: half of 49.3 is antimicrobial resistance -- the mcr-1 colistin resistance plasmid, third and fourth generation cephalosporins, fluoroquinolones, and pigs carrying a greater diversity of mcr variants than other hosts. That is the largest public health story attached to E. coli in pigs and the 8-criterion framework scores it nowhere, C1 measuring transmission of the agent rather than horizontal transfer of a resistance gene. Recorded on all four E. coli entries so the absence is visible.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
Basis. ch49 49.3, the whole public health section for the chapter, and it is about ONE pathotype: "A STEC subgroup known as EHEC, particularly EHEC O157:H7, O26, and other non-O157 serogroups, may be sporadically present in the intestines and feces of pigs and are known to cause bloody diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome in humans infected through food or water contaminated by animal feces. PIGS ARE NOT CONSIDERED A MAJOR SOURCE OF O157 EHEC, AS THE PREVALENCE RATE IS TYPICALLY VERY LOW." Surveys of healthy slaughter pigs: Alberta 1.4%, Japan 1.4%, Ireland 0.21-0.63%, UK 0.3%, Sweden 0.08%, Norway 0.1%, United States 2%.
How this level was decided
Level 1. No human illness is attributable to porcine ETEC or to the atypical EPEC of pigs. NOTE FOR THE REPORT: this records that the pathotype causing postweaning scours is not the pathotype causing human haemorrhagic colitis, not that E. coli is harmless to 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. ch49 49.4.1: "ETEC can be shed in the feces of healthy pigs as part of the intestinal microbiota. Moredo et al. (2015) demonstrated that the percentage of ETEC-positive non-diarrheic pigs was 16.6% during the lactation period, 66% IN THE NURSERY PHASE, and 17.3% in the finisher population." 49.5.1.2: F18 receptor expression is age-dependent, rising through the suckling period and "being highly expressed from about 3 weeks of age", which is why F18 strains cause disease after weaning rather than before. 49.4.5: "Routine cleaning and disinfection are usually insufficient to break the cycle of infection with E. coli."
How this level was decided
Level 1, and the measurement lands precisely on this entry's age group: 66% of NON-DIARRHOEIC nursery pigs carry ETEC. The pathogen is already in two thirds of the pigs at risk, and what changes at weaning is not exposure but the pig -- loss of lactogenic antibody and the switching-on of the F18 receptor. There is no introduction event to prevent. Scored the same as ecoli_neonatal_colibacillosis, the worked example at this level.
C4 Detection difficulty
Difficulty of recognizing and confirming infection
Routine: The disease would be suspected from clinical signs, history and epidemiology in normal practice, and confirmed by tests that local or regional laboratories run routinely
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c4l1, agree with assessment"
Basis. ch49 49.5.2.2: "ETEC diarrhea outbreaks in pigs in the postweaning period vary between farms but are typically seen in the first 3 weeks after weaning... Clinical signs are characterized by yellowish, gray, or slightly pink watery diarrhea with a characteristic smell, generally lasting 1 week." 49.5.4.2: "Culture of the small intestine in ETEC PWD usually yields pure or nearly pure cultures of hemolytic E. coli, as all F18 and most F4 E. coli ETEC are hemolytic. The presence of a significant number of hemolytic colonies is often used as a rapid means for confirming a presumptive diagnosis." PCR virotyping for the fimbrial and toxin genes is described as routine diagnostics.
How this level was decided
Level 1, scored the same as the neonatal worked example and for the same reasons: watery scour in the first three weeks after weaning is recognised in normal practice, and confirmation is overnight culture with haemolysis as a rapid marker plus PCR virotyping at a regional laboratory. The signal is if anything cleaner here than in neonates, because ETEC PWD yields nearly pure haemolytic culture. FLAGGED as a level 1 or 2 judgment: the differential is wider than for neonatal disease -- the chapter names rotaviruses, enteric coronaviruses, salmonellosis and proliferative enteropathy -- and an increasing number of NON-haemolytic F4 strains is being reported, which erodes the rapid marker.
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. ch49 49.1: "The estimated cost of neonatal diarrhea with 10% mortality and low-grade PWD has been reported as $53 and $179 per sow, respectively." 49.5.2.2: "Sudden death can occur, particularly at the start of the outbreak, and mortality can reach up to 25%." Diarrhoea generally lasts one week. For EPEC: "The affected pigs often remain stunted and fail to thrive."
How this level was decided
Level 2, the framework's worked example at this level, and the chapter supplies the figure: $179 per sow per year for low-grade PWD, which is more than three times the neonatal cost and still sits at level 2. Mortality reaches 25% at the start of an outbreak, the diarrhoea runs about a week, and EPEC leaves stunted pigs behind. Small and generally short-lived losses, repeated at every weaning.
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, old disease, never occurs at scale large enough to have market impact"
Basis. No trade measure, movement control or consumer response is recorded anywhere in chapter 49. PWD has been recognised for over fifty years and occurs "in pigs in all countries where pigs are raised commercially".
How this level was decided
INFERRED. Under the standing note SCORING/market_impact this is an agent endemic in every US herd and diagnosed continuously for decades with no historical market move. Level 1, the same as ecoli_neonatal_colibacillosis, which is the worked example.
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, agree with assessment"
Basis. ch49 49.5.6.1: "An outbreak of colibacillosis frequently requires timely antimicrobial therapy, and in many cases, the treatment precedes the results of the sensitivity testing." "Antimicrobial treatment must be selected considering the pharmacokinetic properties of the drugs that reach therapeutic concentrations in the intestinal lumen." Fluid therapy with electrolyte replacement addresses the dehydration and acidosis. Against that: "Escherichia coli strains isolated from cases of neonatal diarrhea, PWD, and ED with variable but usually high rates of resistance toward a wide range of antimicrobial drugs have been described in different countries", and antimicrobials "critically important in human medicine" should be a last resort.
How this level was decided
Level 1, scored with ecoli_neonatal_colibacillosis, which is the framework's worked example, on the ground that the same labelled products treat the same organism in the same pigs a few weeks later. FLAGGED FOR ERIC AS A LEVEL 1 OR 2 JUDGMENT, and it is the sharper case of the two: the chapter reports usually high resistance rates across a wide range of drugs, says the empirical first choice is uncertain, and records that the drugs which would work reliably -- fluoroquinolones, third and fourth generation cephalosporins, colistin -- are the ones reserved for human medicine. Treatment that requires susceptibility testing to be relied on, and whose best options are off limits, is arguably level 2.
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
Corrected by Eric from L2 Available but inconsistent. Reason: "c8l3, upgraded. I think there is a pretty desperate interest in an efficactious post-weaning colibacillosis vaccine in the US. I am unconvinced it exists in the US, autogenous ones in the US don't really work, and we really don't know if the Canadian one will work in US systems - cofactors like herd size, strain differences, parity structure, enviornment, weaning age, etc all impact efficacy. We know for certain it is a significant disease in US, it is commonly treated, it has an AMR problem, and a vaccine would be very useful."
Basis. ch49 49.5.6.3: "Currently, a bivalent live vaccine containing F4 and F18 nonpathogenic E. coli strains has been approved in Europe and Canada for the immunization of pigs against F4- and F18-positive E. coli." "Oral administration of purified F4 or F18 fimbriae as a vaccine significantly reduced fecal excretion of the pathogenic F4 E. coli but did not show protection against pathogenic F18 E. coli infection." "Several studies agree that current commercial vaccines do not provide broad protection against ETEC strains encountered in the field and that the difference among vaccine effects was due to variability in the antigens targeted by the vaccines." "effective protection against PWD can only be achieved by immunizing pigs against the different fimbriae and enterotoxins expressed by various ETEC strains."
How this level was decided
Level 2, and a deliberate split from ecoli_neonatal_colibacillosis at level 1. Vaccines exist -- a bivalent live F4/F18 product is licensed and injectable products are used -- but the chapter states the inconsistency directly: current commercial vaccines do not give broad protection against field strains, oral fimbrial vaccine protected against F4 and not F18, and effective protection would require covering both the fimbrial and the enterotoxin repertoire. Available but inconsistent, which is the level 2 label. FLAGGED ON GEOGRAPHY: the chapter names Europe and Canada as the approving jurisdictions for the live bivalent product and does not say whether it is licensed in the United States. If it is not, this cell is arguably level 3.
Levels and evidence are generated from data/assignments/ecoli_postweaning_diarrhea.yml; the overview is authored in data/overviews/ecoli_postweaning_diarrhea.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.