Clostridium perfringens Type A
LEVELS: Rarely occurs; Mild; Already in the herd; No validated assay; Minor; Negligible; Some; Available but inconsistent
| Register id | clostridium_perfringens_type_a |
| Type | bacteria |
| Scientific name | Clostridium perfringens |
| NCBI taxid | 1502 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Clostridium perfringens type A occupies an unusual place on this register: many swine practitioners are confident it causes neonatal diarrhoea, and the evidence that it does is very weak. The organism is the most ubiquitous C. perfringens type in the intestine of pigs and other animals and is cultured just as readily from healthy piglets as from scouring ones. The disease has never been reproduced by inoculating suckling pigs, Koch's postulates have not been fulfilled, no consistent lesions are reported, and repeated attempts to find a marker that separates pathogenic from commensal strains have failed. Consequently there are no criteria for a definitive diagnosis — finding the organism or its alpha toxin in gut contents is supportive but not diagnostic, because both are present in healthy pigs. The related type F, formerly called CPE-positive type A, is a leading cause of human foodborne illness, but the proportion of such strains in pigs is low, human faecal contamination during handling is now also implicated, and the chapter is explicit that direct contact with swine poses no public health risk.
C1 Zoonotic potential
Likelihood of transmission from pigs to humans
Rarely occurs: Human infection from pigs is plausible but has only rarely been reported, and specific control points are not commonly implemented to prevent transmission to humans
Corrected by Eric from L3 Sometimes occurs. Reason: "c1l2, I think the evidence that pigs are the source of human infection is weak but plausible"
Basis. ch47 47.2.2.2: "The CPE produced by C. perfringens type F (formerly CPE+ C. perfringens type A) is a leading cause of foodborne illness in humans... It usually occurs when CPE-producing type F strains, which contaminate meats, proliferate in meats that are poorly refrigerated or are cooled slowly after cooking. Livestock, including pigs, have been traditionally implicated as the primary source of CPE type F strains through fecal contamination of meat during slaughter. However, the proportion of type F strains in pigs is low... and recent evidence also implicates human fecal contamination of meat during handling as a common source. Direct contact with swine poses no public health risk associated with C. perfringens type F."
How this level was decided
Level 3, and the level 3 structure is stated rather than inferred: a known foodborne route, through faecal contamination of meat at slaughter, that produces illness only when refrigeration or cooling fails. Both control points are named in the chapter. FLAGGED ON REGISTER SCOPE, and this is a question for Eric rather than a scoring judgment: the human agent is toxinotype F, which under the current nomenclature is a DIFFERENT toxinotype from the registered type A, and the chapter says the proportion of type F in pigs is low and that direct contact with swine poses no risk. If the entry is read strictly as CPE-negative type A, this cell is level 1. It is scored level 3 because the chapter puts this material in its Public Health section for type A.
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. ch47 47.2.2.2: human illness is "characterized by abdominal cramping, nausea, and diarrhea".
How this level was decided
Level 2. The chapter names the whole clinical picture and it is a short self-limiting gastroenteritis -- cramping, nausea and diarrhoea, with no hospitalisation, complication or mortality mentioned. Usually mild with serious disease rare is level 2 exactly.
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. ch47 47.2.2: "the ease with which C. perfringens type A is cultured from diarrheic and clinically normal neonatal pigs, since it is well established as a normal component of the intestinal microbiota". 47.2.2.1: "This toxin and C. perfringens type A are very frequently found in the intestine of healthy animals and the environment." 47.2.2: "C. perfringens type A is the most ubiquitous type in the intestine of most animals, including piglets."
How this level was decided
Level 1 word for word -- carried by the pigs themselves, so there is no introduction event to prevent. The chapter states it three separate times, and the whole diagnostic problem for this entry follows from it. This is the same shape as streptococcus_suis and the other biome organisms, which is the case level 1 was rewritten for.
C4 Detection difficulty
Difficulty of recognizing and confirming infection
No validated assay: No pathogen-specific test of known reliability exists anywhere, and identification depends on sequencing or on primers that have not been critically evaluated
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c4l4, agree with assessment - this deserves an explanatory note for exactly the reason you describe in your assessment - it is hard to understand when the agent is causative versus just present."
Basis. ch47 47.2.2.5: "Currently, no criteria are available to establish a definitive diagnosis of type A enteritis in pigs." "Detection of CPA in intestinal contents is supportive but nondiagnostic because this toxin can be found in the intestinal content of healthy pigs." "Currently, no commercial assays are available to detect CPB2, and the significance of finding this toxin in the intestine of pigs is uncertain." 47.2.2: "Koch's postulates have not been fulfilled for C. perfringens type A infections in pigs, and diagnostic criteria have not been established." Attempts to find a marker distinguishing pathogenic from commensal strains "have so far failed".
How this level was decided
Level 4, and it needs a word of explanation because it is not the usual level 4 case. Finding the ORGANISM is trivial -- it cultures easily and multiplex PCR toxinotypes it reliably. What does not exist is any test that establishes the DISEASE, because the organism is normal flora and no marker separates a pathogenic strain from a commensal one. The chapter says in terms that no diagnostic criteria exist. Under the C4 axis -- whether a validated assay exists for the thing being diagnosed -- that is level 4: no pathogen-specific test of known reliability exists anywhere. FLAGGED for Eric as the case that stretches the label, since the level 4 wording points at sequencing and unevaluated primers and here the failure is one of attribution rather than of technique.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c5l2, still seems to be some uncertainty about clinical effect of this disease because experimental evidence is lacking. However, field evidence suggests is a real pathogen"
Basis. ch47 47.2.2: "Although this microorganism has been associated with neonatal diarrhea and many swine practitioners are confident of its role, the disease has not been reproduced in inoculation studies in suckling pigs." "there being abundant testimonial association with disease but very little experimental evidence supporting C. perfringens type A as a cause of enteric disease in mammals." 47.2.2.4: "No consistent and few inconsistent lesions are reported."
How this level was decided
INFERRED, and the uncertainty is about causation rather than about cost. Practitioners attribute neonatal diarrhoea to type A and treat for it, so there is real spending attached to this entry whatever the truth of the attribution -- but the disease has never been reproduced experimentally, no consistent lesion exists, and the chapter calls the epidemiology "highly speculative". Small losses is the honest reading. Level 2. FLAGGED: level 1 is defensible on the ground that an entity that cannot be diagnosed and has not been reproduced cannot be shown to cost anything.
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 with no evidence to suggest diagnosis would impact markets"
Basis. Section 47.2.2 records no trade measure, movement control or consumer response, and describes the organism as normal intestinal microbiota of most animals.
How this level was decided
INFERRED. Under the standing note SCORING/market_impact, an organism that is normal flora in every pig and has been cultured from healthy and diarrhoeic piglets for decades has no route to pork supply or demand. 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
INFERRED — reasoned, not stated. The evidence implies this level rather than stating it. The reasoning is below.
Corrected by Eric from L1 Little. Reason: "c7l2, farms that have diagnosed this disease have treatment options available albeit with variable efficacy."
Basis. ch47 47.2.2 and its subsections describe no treatment for type A enteric disease. The chapter's position is that the entity itself is not established: "Koch's postulates have not been fulfilled... and diagnostic criteria have not been established."
How this level was decided
INFERRED. Under the standing note SCORING/treatment_potential, level 1 covers the case where there is no imperative to treat. Here the reason is unusual: the organism is normal flora in every pig, so there is nothing to eliminate, and the disease attributed to it has never been reproduced. A treatment cannot be shown to improve an outcome that cannot be attributed. FLAGGED as the weakest cell in this entry -- practitioners do medicate neonatal diarrhoea and would say a treatment exists, which would make this level 2 on extralabel use.
C8 Vaccine availability
Availability of effective vaccines or bacterins
Available but inconsistent: Commercial or autogenous vaccines exist in the US but protection may be inconsistent
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c8l2, autogenous being made on demand and I think there was actually a commercial vaccine available at one time but again, the disease is plagued by a lack of high quality repeatable experimental model and evidence"
Basis. No vaccine is described for C. perfringens type A in ch47. C. perfringens type A is the named worked example for this level in criteria_levels.yml.
How this level was decided
INFERRED FROM THE FOLDER, FIXED BY THE FRAMEWORK. The chapter says nothing about type A vaccines, but criteria_levels.yml names C. perfringens type A as a worked example at C8 level 2 alongside PRRSV and influenza A, so this cell is settled by the framework rather than judged here. Level 2 is also the right reading on the merits: commercial and autogenous type A toxoids are used in US sow herds, and protection is inconsistent -- which is exactly what a vaccine against an agent of unproven causal role would look like.
Levels and evidence are generated from data/assignments/clostridium_perfringens_type_a.yml; the overview is authored in data/overviews/clostridium_perfringens_type_a.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.