Botulism
LEVELS: Highly unlikely; Severe; Routine biosecurity keeps it out; Reference or research laboratory required; Negligible; Negligible; Some; Available, or not needed
| Register id | clostridium_botulinum |
| Type | bacteria |
| Scientific name | Clostridium botulinum |
| NCBI taxid | 1491 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Clostridium botulinum produces botulinum neurotoxin, which blocks nerve signals to muscle and causes a progressive flaccid paralysis. Pigs are among the least susceptible domestic animals and the disease is genuinely rare in them, probably because the pig gut absorbs the toxin poorly. The handful of recorded outbreaks all trace to eating something they should not have — dead fish, decomposing brewery waste, improperly preserved restaurant waste — with 13–29% of exposed pigs affected and similar mortality. Affected animals become weak and uncoordinated, stagger, salivate, develop dilated pupils and laboured breathing, and die when the muscles of respiration fail. Diagnosis rests on demonstrating toxin in feed, gut contents, liver or serum rather than on finding the organism. Because the disease follows a feeding accident rather than an infection passed between pigs, prevention means controlling what the herd can eat; vaccination is not practical for something this rare.
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. ch47 47.4: "Neurotoxic clostridial diseases include tetanus caused by C. tetani and botulism caused by C. botulinum. Neither disease is zoonotic; hence, there is no public health concern."
How this level was decided
Level 1, stated outright. Human botulism is a serious disease but it is an intoxication acquired from the same environmental and food sources, not something transmitted from a pig. There is no evidence that pigs transmit the agent to humans, which is the level 1 test.
C2 Zoonotic impact
Severity of human illness caused by the agent
Severe: Infection carries a substantial risk of life-threatening illness, death, or permanent disability, even if human infections are uncommon
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c2l4, severe disease in humans". Same evidence limitation as tetanus and settled the same way: ch47 47.4 covers both diseases in the one sentence that says neither is zoonotic, so the folder cannot grade human botulism and his ruling supplies the level. C1 records separately that pigs are not a source.
Basis. ch47 47.4: "Neither disease is zoonotic; hence, there is no public health concern."
How this level was decided
RE-SCORED 2026-09-04. C2 now grades the severity of the illness the agent causes in a person, independent of how the person was exposed -- the 2026-09-01 pig-attribution reading is reversed, and C1 alone carries the source question. Botulism is a life-threatening flaccid paralysis requiring ventilation. Same evidence limitation as tetanus: ch47 47.4 says only that neither disease is zoonotic.
PREVIOUS ANSWER, written under the pig-attribution reading: Level 1, following from C1. NOTE FOR THE REPORT, because this is exactly the label Eric has caught inverting before: this is not a finding that botulinum toxin is harmless to people. It records that pigs are not a source of it.
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. "c3l3, agree with assessment"
Basis. ch47 47.4.2.1: "Spores are ubiquitous in soil throughout the United States." "Botulism in swine is rare, so there are few recorded organism or toxin sources, but disease in swine due to consumption of dead fish, decomposing brewery waste, and restaurant waste has been reported." "Eating habits of non-confined pigs should make them likely candidates for botulism, but there appears to be innate resistance to toxin administration by the oral route." A series of type C outbreaks followed "consumption of residues from restaurants that were inadequately preserved during the summer". 47.4.2.5: "Prevention requires eliminating opportunities to consume potentially toxic material such as spoiled garbage and decomposing animal tissue."
How this level was decided
Level 3, and this is the first genuinely contested C3 under the new five-level ladder, so the reasoning is set out. The spores are ubiquitous in US soil, which looks like level 5 -- but what reaches the pig is PREFORMED TOXIN in spoiled material, and the chapter says prevention is eliminating the opportunity to eat it. Feed sourcing, garbage exclusion and prompt carcass removal are a routine biosecurity programme, run continuously and capable of failing, which is level 3. The chapter also supplies a level 2 reading -- "eating habits of NON-CONFINED pigs should make them likely candidates" -- but the outbreaks actually on record came through fed restaurant waste rather than through scavenging, and confinement does not stop what you put in the trough. Highest level wins, so level 3. FLAGGED for Eric as the cell where the new ladder is doing real work.
C4 Detection difficulty
Difficulty of recognizing and confirming infection
Reference or research laboratory required: A validated assay exists, but only at a national reference or research laboratory rather than at local or regional level
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c4l3, agree with assessment"
Basis. ch47 47.4.2.4: "A diagnosis of botulism should be considered in afebrile, alert animals with progressive weakness and recumbency. Because the pig apparently is resistant to botulism, a diagnosis should be made only after thorough investigation and exclusion of other possible diagnoses." "Confirmation of the diagnosis should be based on detection of BoNT in feed, gastrointestinal contents, liver, or serum. Mouse bioassay is still the test most frequently used around the world, although the sensitivity of the test is usually low. The sensitivity of this test is highest for feed, intermediate for gastrointestinal content and liver, and lowest for serum." 47.4.2.3: "There are no specific gross or microscopic lesions."
How this level was decided
Level 3. A validated assay exists -- the mouse bioassay is the recognised reference method for botulinum neurotoxin -- but it is a live-animal bioassay run at national reference and public health laboratories, not something a regional veterinary diagnostic laboratory offers. That is the level 3 test exactly. The clinical route is closed too: no specific lesions, and the chapter says a diagnosis should be made only after excluding everything else. FLAGGED as a level 3 or 4 judgment: the chapter says the bioassay's sensitivity is usually low and lowest of all in serum, and a test that misses cases is arguably a test of unknown reliability. Scored level 3 because low sensitivity in a validated reference method is a known limitation rather than an unevaluated one.
C5 Production cost
Financial impact on the infected farm's cost of production
Negligible: No measurable effect on 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. "c5l1, virtually never seen clinically except in rare instances of spoiled waste food, usually on noncommercial farms"
Basis. ch47 47.4.2: "Swine are susceptible to botulism but are in general considered to be among the least susceptible domestic animals." 47.4.2.1: "Botulism in swine is rare." "there appears to be innate resistance to toxin administration by the oral route. The swine gastrointestinal tract may have a low permeability for botulinum toxin." Against that: "A morbidity of 13-29% and a mortality of 13-24% were reported in a series of outbreaks of botulism type C in swine associated with consumption of residues from restaurants that were inadequately preserved during the summer."
How this level was decided
INFERRED. The outbreak figures are substantial -- up to a quarter of exposed pigs dead -- but they come from feeding inadequately preserved restaurant waste, which is not modern US production, and the chapter says twice that swine are among the least susceptible domestic animals and that botulism in them is rare. Under the standing note SCORING/production_cost_impact this is scored on modern US production, where the exposure route is essentially closed. No measurable effect on cost of production. Level 1. FLAGGED because the mortality figures on the page argue against the level, and the whole weight of the argument is that the exposure does not occur 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, old disease with no evidence to suggest diagnosis would impact markets"
Basis. Section 47.4.2 records no trade measure, movement control or consumer response for swine botulism, and chapter 47 states that botulism is not zoonotic.
How this level was decided
INFERRED. Under the standing note SCORING/market_impact, botulism spores are ubiquitous in US soil and swine botulism has been recognised for decades without a market move on record, and the chapter closes the route that might cause one by saying the disease is not zoonotic. Level 1. NOTE: "botulism" is a word with unusual power in a food context, and a pork-associated human case would not behave like this level -- but that would be a new fact rather than the recurrence of an old one, and C6 records what the market has done.
C7 Treatment potential
Potential for treatment to improve outcomes
Some: Treatment exists but is inconsistent, requires extralabel use, or works only in some circumstances
Basis. ch47 47.4.2.5: "Antitoxin is the only specific treatment for botulism, and it has been effective in reducing mortality in humans after consumption of toxin-containing food. Polyvalent antitoxins incorporating the types most commonly present in a geographic area are required for therapy in animals. Therapy aimed at reducing continued absorption of toxin from the intestine (administration of magnesium sulfate) might be helpful."
How this level was decided
Level 2. A specific treatment exists and works -- antitoxin, proven in humans -- but it must be polyvalent and matched to the toxin types in the region, it is not a labelled swine product, and by the time flaccid paralysis is recognised much of the toxin is already bound. Treatment that exists but requires extralabel use and works only in some circumstances is level 2 under the standing note SCORING/treatment_potential.
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
Basis. ch47 47.4.2.5, in the chapter's own words: "Prophylactic immunization with toxoids is not practical in swine because of the infrequent occurrence of the disease."
How this level was decided
Level 1 on the second clause, and the chapter states the clause rather than implying it. Botulinum toxoids exist and are used in other species; the chapter's judgment is that the disease is too infrequent in swine to justify using one. That is precisely what "or the disease does not clinically or economically justify vaccinating" was widened to hold in the 2026-08-28 C8 rework.
Levels and evidence are generated from data/assignments/clostridium_botulinum.yml; the overview is authored in data/overviews/clostridium_botulinum.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.