Anthrax
LEVELS: Sometimes occurs; Severe; Housing alone keeps it out; Routine; Negligible; Negligible; Little; Available, or not needed
| Register id | bacillus_anthracis |
| Type | bacteria |
| Scientific name | Bacillus anthracis |
| NCBI taxid | 1392 |
| Evidence | 2 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Bacillus anthracis is the bacterium that causes anthrax. It is best known in cattle and sheep, but pigs can be infected, and the organism matters here for two reasons: it is genuinely zoonotic, and its spores are almost indestructible — they remain viable in soil for fifty years or more. Pigs are relatively resistant compared with ruminants. Rather than the rapidly fatal septicaemia seen in cattle, an infected pig usually develops a milder subacute or chronic illness with swelling of the throat, fever and enlarged lymph nodes, and many recover. Some carry the organism in tonsils and cervical lymph nodes for months with no outward sign at all, which is why cases are occasionally first noticed at slaughter. Infection comes from the environment rather than from other pigs, so control is a matter of keeping animals away from contaminated soil, feed and carcasses rather than of ordinary herd biosecurity. In the United States it is enzootic in defined regions and reportable, and feral swine show high exposure — 43.7% of Texas samples were seropositive. Humans are infected mainly by handling carcasses or eating undercooked meat, and the inhaled form is often fatal.
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. "anthrax is zoonotic, and infected swine and their pork products are a hazard to humans." "Human exposure occurs when animals that have died from the disease are examined postmortem without appropriate precautions or during carcass disposal." "Ingestion of vegetative forms of B. anthracis in undercooked, contaminated pork can lead to anorexia, bloody diarrhea, and abdominal pain that may progress to fatal septicemia and toxemia." (ch58 58.2.1)
How this level was decided
Two pig-to-human routes are named -- occupational exposure at necropsy and carcass disposal, and ingestion of undercooked contaminated pork -- and both are governed by control points the chapter itself specifies: "Necropsy of anthrax cases is discouraged", precautions during disposal, and meat inspection. Transmission follows failure of those control points. Level 3.
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
Basis. "Infection through open skin wounds causes focal cellulitis and lymphadenitis in humans that is often self-limiting. More serious is the inhalation of spores that leads to flu-like symptoms and progresses to sepsis and toxemia that is often fatal." "Ingestion of vegetative forms... may progress to fatal septicemia and toxemia." (ch58 58.2.1)
How this level was decided
The cutaneous form is self-limiting, but the two forms arising from the swine exposure routes -- inhalational from sporulated material during carcass handling, and gastrointestinal from contaminated pork -- are both described as often fatal. A substantial risk of life-threatening illness is level 4, and the level 4 label applies "even if human infections are uncommon", which covers the rarity of porcine anthrax.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Housing alone keeps it out: Raising pigs indoors and off soil breaks the cycle, so no ongoing biosecurity program is needed and only outdoor herds stay exposed
Basis. "Spores can remain viable under appropriate environmental conditions for 50 or more years." "In the United States, feral swine in both endemic and nonendemic regions have high levels of seropositivity to B. anthracis, with overall levels of 43.7% in samples from Texas (Maison et al. 2021)." "Control of the spread of anthrax differs significantly from control of most other animal diseases because it depends on preventing access to viable spores of B. anthracis in soil, manures, or contaminated feeds." (ch58 58.2.1, 58.2.2, 58.2.5)
How this level was decided
MOVED L5 -> L2 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. soil spores, and Eric had already written the level 2 clause about this entry: "it would only be clinically relevant for outdoor herds where the organism is, or has been known, to be present. We tend not to raise pigs in these enviornments at any important scale."
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. Two reservoirs outside the pig industry, both established in the US: soil spores that persist for half a century, and feral swine at 43.7% seropositivity in Texas. The chapter states plainly that control depends on preventing access to environmental spores rather than on herd biosecurity. That is the level 4 definition, and the US reservoir the level 4 label requires is present.
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
Corrected by Eric from L3 Reference or research laboratory required. Reason: "l1, the combination of history, clinical signs, and easy culture should generate a diagnosis quickly at most labs. The idea of silent or chronic infections is possible but not characteristic of the disease."
Basis. CFSPH 2017: "Some apparently healthy pigs can have anthrax lesions in the cervical lymph nodes and tonsils at slaughter." "B. anthracis has been reported to persist for months in the lymph nodes and tonsils of some healthy pigs." "Bacteremia is rare in pigs, and a small piece of affected lymphatic tissue is often collected aseptically instead." ch58 58.2.4: "Diagnosis of anthrax in swine is made difficult by its rare occurrence, lack of unique clinical signs, and similarity of various forms to other more common swine diseases."
How this level was decided
Level 3 unchanged and now better supported. The factsheet adds a second reason beyond the chapter's: not only is the presentation non-specific, but infection can be entirely silent and surface only as lymph node lesions at slaughter, and the standard blood-smear diagnosis used in ruminants does not work in pigs because bacteraemia is rare. Confirmation still runs through a reference laboratory under select agent handling.
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. "should be c5l1, anthrax is a non-player in virtually all farms. It would only be clinically relevant for outdoor herds where the organism is, or has been known, to be present. We tend not to raise pigs in these enviornments at any important scale. The disease is almost never seen anymore in domestic pigs."
Basis. CFSPH 2017: "Pigs, other omnivores and carnivores are more resistant to disease, but they can become ill if the dose is high." "More often, pigs have mild subacute to chronic cases characterized by localized swelling, fever and enlarged lymph nodes." "Some pigs with anthrax recover." "Among domesticated animals, clinical cases are usually fatal in domesticated ruminants and horses, while pigs often recover."
How this level was decided
MOVED L3 -> L1, and the new factsheet settles it in Eric's favour rather than mine. My L3 reasoned from the mandated response -- carcass incineration, premises decontamination -- and inferred a real one-off cost. He corrected to L1: "anthrax is a non-player in virtually all farms... The disease is almost never seen anymore in domestic pigs." The CFSPH sheet supplies the biology behind that: pigs are resistant, the usual course is mild subacute or chronic, and they often recover where ruminants and horses die. A response cost that is almost never incurred is not a measurable increase in cost of production. The pass now agrees with his correction rather than being overridden by it.
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. "should be c6l1, anthrax is well known in ruminant industries so a diagnosis in the pig industry would likely not attract any attention in the market. I suppose there could be a large mortality event, on a single herd somewhere that would cause some local interest but even still, would be unlikely to have any general effect on markets."
Basis. CFSPH 2017 describes anthrax as enzootic in defined regions of the US and reportable, with control resting on carcass disposal and premises decontamination. It records no trade measure, movement standstill or consumer response arising from a swine diagnosis. Eric, 2026-08-27: "anthrax is well known in ruminant industries so a diagnosis in the pig industry would likely not attract any attention in the market."
How this level was decided
MOVED L2 -> L1 under the standing note SCORING/market_impact, which this entry fits exactly: an agent already present and already diagnosed in the US, with no historical evidence of a market move following a diagnosis. That is the test the note sets, and it returns 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
Basis. "Pigs with clinical anthrax can recover completely after penicillin treatment (Ferguson 1986). Oxytetracycline is effective against B. anthracis and may be used parenterally." "Immunity develops in recovered animals." (ch58 58.2.5)
How this level was decided
C7 scores the size of the opportunity a treatment would create. Complete recovery on penicillin is recorded, a second effective drug is named, and pigs are separately described as resistant and often surviving anyway. Both halves of level 1 are satisfied -- effective treatment is available AND animals largely recover without it -- so there is little room for a new treatment to improve outcomes.
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
INFERRED — reasoned, not stated. The evidence implies this level rather than stating it. The reasoning is below.
Corrected by Eric from L2 Available but inconsistent. Reason: "c8l1, the vaccine literature is old but still accurate. There is good supply of vaccine in the market and it is labelled for pigs (https://colorado-serum- com.3dcartstores.com/anthrax) though is rarely used because prevalence and risk is low in pigs."
Basis. "Vaccines can stimulate protective immunity. Kaufmann et al. (1973) used the Sterne strain anthrax vaccine, an avirulent spore vaccine, in swine with success." (ch58 58.2.5)
How this level was decided
INFERRED. A vaccine exists, is named, and is recorded as working in swine, which rules out level 3. But the single supporting study is from 1973, the Sterne vaccine is a livestock product not marketed for swine, and anthrax vaccination is not part of any standard US swine programme. Level 2 -- exists, but protection in this species is not established as consistent. If Eric judges the Sterne vaccine practically available for swine use in the US, this is level 1.
Levels and evidence are generated from data/assignments/bacillus_anthracis.yml; the overview is authored in data/overviews/bacillus_anthracis.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.