Swine Tuberculosis
LEVELS: Sometimes occurs; Moderate; Extraordinary biosecurity required; Reference or research laboratory required; Moderate; Negligible; Some; Needed but not available
| Register id | mycobacterium_avium_complex |
| Type | bacteria |
| Scientific name | Mycobacterium avium complex (MAC) |
| NCBI taxid | 120793 |
| Evidence | 3 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
The Mycobacterium avium complex, chiefly M. avium subsp. hominissuis, causes tuberculosis in pigs — though almost never the illness the word suggests. Infection in swine is usually silent, and producers typically learn of it only at slaughter, when granulomas are found in the lymph nodes of the head or gut. The organism is ubiquitous in the environment rather than passed pig to pig; organic bedding and biofilms in water systems are the documented sources, and chlorinated water lines suit it particularly well. Because the pig is rarely ill, the cost is entirely a carcass one, and it is a real one: US regulations require that a carcass with tuberculous lesions in more than one primary site be cooked, and since most high-volume plants have no cooking facilities the carcass is condemned instead. Diagnosis cannot be made clinically, and the gross lesions are not specific — Rhodococcus equi produces a similar picture. In people MAC is an opportunist affecting mainly the immunocompromised, those with chronic lung disease and the elderly, and no evidence links human infection to contact with pigs or to eating pork.
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
Corrected by Eric from L1 Highly unlikely. Reason: RULED C1L3 on 2026-09-01. Eric had already written the argument into his C2 ruling on this entry before C2 was rescoped: "c2l3 is correct, though it seems pigs are only rarely if ever the source of infection in people (making it l2) we do have slaughter control points to identify it's presence and therefore it requires a breakdown of the control point for pigs to be the source". That last clause is the C1 level 3 definition word for word -- a known risk of transmission to humans that requires the failure of one or more control points -- and the cell had been scored level 1. Asked to confirm which criterion he meant, he chose C1 to level 3. CONSEQUENCE, and it is the reason this matters: with C1 at level 3 the pig IS a source, so his C2 level 3 stays exactly where he put it rather than following the other five down to level 1, and the C1L1-implies-C2L1 check no longer flags this entry.
Basis. "MAC, especially MAH, is an opportunistic infection that rarely causes disease in immunocompetent individuals. Risk factors for infection in humans include immunocompromised, chronic pulmonary disease, and advanced age. Chlorination of water delivery systems provides a preferential environment for proliferation of MAC and other nontuberculous mycobacteria in biofilms. No data implies exposure to infected swine or consumption of pork as an increased risk for human infection." (ch58 58.9.3)
How this level was decided
The chapter answers C1 in its own words: no data implicates exposure to infected swine or pork consumption as a risk for human infection. People acquire MAC from the environment, characteristically from water-system biofilms, and the pig is not the source. That is level 1 under the corrected "from pigs" label. NOTE: this is a case where the old L1 wording would have been false -- MAC infects humans readily -- and the relabelling Eric ruled on is what makes level 1 the right and readable answer.
C2 Zoonotic impact
Severity of human illness caused by the agent
Moderate: Clinically important illness is common and may require medical treatment or hospitalization, but death or permanent disability is uncommon
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c2l3 is correct, though it seems pigs are only rarely if ever the source of infection in people (making it l2) we do have slaughter control points to identify it's presence and therefore it requires a breakdown of the control point for pigs to be the source of a human case."
Basis. ch58 58.9.3: MAC "is an opportunistic infection that rarely causes disease in immunocompetent individuals. Risk factors for infection in humans include immunocompromised, chronic pulmonary disease, and advanced age." CFSPH 2020 paratuberculosis adds that reports of paratuberculosis in pigs "are rare, and date from before the advent of nucleic acid methods", so MAP is not the swine agent and its human associations do not attach to this entry.
How this level was decided
Level 3 unchanged, still INFERRED. The paratuberculosis factsheet earns its thin placement here by ruling something out rather than in: it closes off the MAP-and-Crohn's question, which would otherwise hang over a MAC entry, by showing MAP is barely a pig organism at all. Human MAC disease remains a chronic pulmonary or disseminated infection of the immunocompromised requiring prolonged therapy, with no case fatality in the folder to anchor level 4.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Extraordinary biosecurity required: Exclusion needs measures beyond the routine, such as air filtration, thermally treated feed and bedding, or repeated costly testing to find carriers, and may still fail
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED at level 4 on the C3 review sheet. "l4, keep at l4 primarily as a function of the contaminated bedding issue - you would need guarantees that bedding had not been contaminated by bird feces or that the bedding had been autoclaved. Somewhere between L3 and l4, but we will leave at l4" This is the one entry in the batch where a level 4 rests on something INSIDE the barn -- contaminated bedding -- rather than on a vector or on incoming pigs. Autoclaved or guaranteed-clean bedding is the extraordinary measure.
Basis. CFSPH 2019 bovine tuberculosis: "Other maintenance hosts include wood bison around Wood Bison National Park, Canada, feral swine in parts of Hawaii, brush-tailed opossums in New Zealand, European badgers in the United Kingdom", and wild boar are "thought to be important maintenance hosts in Mediterranean climates on the Iberian Peninsula". ch58 58.9.4: MAH "is ubiquitous in the environment", and organic bedding and water-system biofilms are the documented risk factors.
How this level was decided
RENUMBERED L5 -> L4 on 2026-09-03, when C3 was reduced from five levels to four and level 4 absorbed level 5. THE JUDGMENT IS UNCHANGED and this one really is a renumber: the merged level 4 label carries what level 5 said, ending "and may still fail". IT WAS STILL CHECKED rather than assumed, because the last renumber on 2026-09-01 was mechanical and moved twenty-one entries past a level they should have been judged against. The check is the exclusion test -- does housing close the route? For this entry it does not.
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. Level 4 unchanged and now supported from two directions rather than one. The chapter established the environmental reservoir for MAC; the factsheet adds an established wildlife maintenance reservoir for MTBC that includes FERAL SWINE IN THE US, in Hawaii. ch58 says that where MTBC is endemic in feral swine it must be considered alongside MAC as a cause of swine tuberculosis, so this is on entry rather than beside it. Either reservoir alone gives continuous opportunity for exposure outside the pig industry.
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. "l3, though many L2 labs could also have very strong opinion, referral is likely" Transcribed by the assistant and confirmed by Eric on 2026-08-31 -- "i confirm the six". The harvester refused it because the comment names two levels, but the second is a noun phrase for a level-N-capable laboratory rather than a second assignment.
Basis. "Tuberculosis in swine is usually subclinical, and therefore swine producers typically become aware of it at slaughter." "A clinical diagnosis of tuberculosis in swine is usually not possible since most cases are asymptomatic." "Gross lesions of granulomatous lymphadenitis or disseminated granulomas are sufficient for tuberculosis to be included as a possible cause but are not sufficiently specific for a definitive diagnosis. R. equi and other bacteria can cause granulomatous lymphadenitis grossly and microscopically indistinguishable from tuberculosis." "An unequivocal diagnosis requires confirmation of the Mycobacterium spp. in tissues with lesions by culture and identification or by direct PCR." "Submit all samples to a laboratory specializing in mycobacterial culture." "several ELISAs for MAC in swine have been evaluated, and some have recently been commercialized (although not sold in the United States)." "For the US, PPDs are available from the NVSL, Ames, IA." (ch58 58.9.6, 58.9.8)
How this level was decided
Every route to a diagnosis leads out of the local laboratory. There is no clinical presentation, the gross lesions are indistinguishable from R. equi and Trueperella abscesses, the serological assays are not sold in the US, the PPD for skin testing comes from NVSL, and the chapter instructs that samples go to a laboratory specialising in mycobacterial culture. Level 3.
C5 Production cost
Financial impact on the infected farm's cost of production
Moderate: Losses measurably increase cost of production but remain manageable within normal farm operations, whether acute, chronic, or associated with endemic disease
Basis. "The processing of swine carcasses with tuberculosis is costly and results in significant economic losses. Regulations of the US Department of Agriculture require that unaffected portions of swine carcasses with tuberculous lesions in more than one primary site, such as cervical and mesenteric lymph nodes, be cooked. In processing plants where cooking facilities are not available (most high-volume modern plants), the carcass is condemned." "In most outbreaks, attention to these factors eliminates or greatly reduces slaughter condemnations. However, in some confined herds with few apparent risk factors, it may be difficult to consistently reduce condemnations." (ch58 58.9.1, 58.9.9)
How this level was decided
The chapter states the cost directly -- whole-carcass condemnation at modern plants, described as significant economic losses -- and it falls on the farm that shipped the pigs. It stays at level 3 rather than level 4 because the chapter also says attention to bedding and water eliminates or greatly reduces condemnations in most outbreaks, which is a manageable problem, and because national prevalence had fallen to 0.0068% by 2016.
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 is correct, the agent is well known and not a surprise finding. It typically shows up as a condemnation event from finishing pigs that have been housed on bedding contaminated with bird feces. Even in the rare case when a notable large condemnation event occurs, it historically does not effect markets."
Basis. "The percentage of swine with suspect tuberculous lesions at slaughter peaked in 1922 and has progressively reduced since." "The prevalence by 2008 and 2016 had decreased to 0.0178 and 0.0068%, respectively." "Because it is required for export to several countries, most agriculture ministries make purified protein derivatives (PPDs) from the various Mycobacterium spp. important in that country or region available for testing." (ch58 58.9.1, 58.9.4, 58.9.8.1)
How this level was decided
INFERRED. At 0.0068% of slaughtered pigs, swine tuberculosis is a carcass-disposition matter handled inside the plant, not an event that moves the supply of or demand for pork. No movement control, standstill or market closure follows a condemnation. Level 1. NOTE: the chapter records that skin testing is required for export to several countries, so a herd with a testing problem could lose eligibility for particular markets. That is a standing trade requirement rather than a disruption triggered by disease occurring, which is what C6 measures -- but it is the reason someone might argue level 2.
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 L3 Substantial. Reason: "there is not a great fit for the rating but I would choose C7l2, the occurrence is very sporadic, with known risk factors, and causes no clinical disease in pigs therefore is only diagnosed post-mortem with no opportunity for treatment. It certainly is not L1 and i am reluctant to make it l3, therefore l2 it is."
Basis. The Prevention and Control section is entirely environmental -- avoiding wood shavings, sawdust and peat as bedding, clearing standing water, removing biofilms from water systems, tuberculocidal phenolic disinfectants, and skin-testing and culling sows. No antimicrobial treatment of infected pigs is described anywhere in the section. "in some confined herds with few apparent risk factors, it may be difficult to consistently reduce condemnations." (ch58 58.9.9)
How this level was decided
INFERRED, and a cell worth a ruling. No pathogen-directed treatment for swine tuberculosis is offered, and the chapter reaches for culling instead. C7 asks the size of the opportunity: a treatment that cleared granulomas would remove the carcass condemnations the chapter calls significant economic losses, including in the confined herds it says cannot reliably fix the problem environmentally. That is a meaningful improvement, so level 3. The alternative reading is level 1 -- infection is subclinical, the pig itself is unharmed, and there is no animal outcome to improve. This entry differs from campylobacter_spp, scored level 1 on exactly that reasoning, because MAC produces lesions that cost money and Campylobacter produces nothing.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c8l3 is correct, no vaccine to my knowledge is licensed for swine though in theory in high-risk settings (in fact there is recent increase in use of bedding based housing) one could see value in vaccination"
Basis. ch58 58.9.9 names bedding management, water system remediation, disinfection, skin testing and culling, and no vaccine. Eric, 2026-08-27: "no vaccine to my knowledge is licensed for swine though in theory in high-risk settings (in fact there is recent increase in use of bedding based housing) one could see value in vaccination".
How this level was decided
STAYS L3, and his own words are why. Alone among the ch58 entries he confirmed at level 3, he did not say a vaccine was unwarranted -- he said he could see value in one, and named a trend increasing the need. Carcass condemnation is a stated significant economic loss. That is a genuine unmet need, which is exactly what the reworded level 3 is now reserved for.
Levels and evidence are generated from data/assignments/mycobacterium_avium_complex.yml; the overview is authored in data/overviews/mycobacterium_avium_complex.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.