Proliferative Enteropathy
LEVELS: Highly unlikely; No human illness; Already in the herd; Laboratory-dependent; Moderate; Negligible; Little; Available, or not needed
| Register id | lawsonia_intracellularis |
| Type | bacteria |
| Scientific name | Lawsonia intracellularis |
| NCBI taxid | 29546 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Lawsonia intracellularis causes proliferative enteropathy, usually called ileitis: the bacterium multiplies inside the cells lining the intestinal crypts and drives them to divide, thickening the gut wall. It is close to universal — about 96% of farm sites are infected, and roughly 30% of weaner-to-finisher pigs carry lesions. It shows up in three ways. The acute haemorrhagic form hits young adults and replacement gilts with bloody diarrhoea and sudden deaths. The chronic form affects pigs from six to twenty weeks with loose faeces and poor growth. Most infection, though, is subclinical: no diarrhoea at all, just pigs that eat the same and grow more slowly, which is where most of the loss sits and why it is routinely underestimated — around US$1–5 per affected growing pig. The organism cannot be grown on ordinary laboratory media, which is why diagnosis depends on PCR and histology rather than culture. Control combines hygiene, rodent control and all-in/all-out flow with vaccination, and both oral modified-live and injectable killed vaccines are available and effective.
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. ch51 51.3, and it is an EXAMINED negative rather than a silence, which is unusual and worth the space: "THERE IS NO EVIDENCE OF L. INTRACELLULARIS INFECTION IN HUMANS. A SURVEILLANCE STUDY IN CHILDREN LIVING ON EUROPEAN PIG FARMS FAILED TO FIND L. INTRACELLULARIS DNA IN THEIR FECAL SAMPLES (Jacobson et al. 2007). INVESTIGATIONS OF CROHN'S DISEASE AND OTHER MUCOSAL INFLAMMATORY CONDITIONS OF HUMANS HAVE CONSISTENTLY FAILED TO FIND TYPICAL PE LESIONS OR L. INTRACELLULARIS (Michalski et al. 2006)." 51.4 records a wide non-human host range -- hamsters, rabbits, ferrets, foxes, dogs, sheep, deer, ratites, horses and nonhuman primates -- with people absent from it.
How this level was decided
Level 1, and this is one of the few C1 cells in the register resting on somebody having LOOKED. The most exposed human population there is -- children living on pig farms -- was screened and was negative, and the obvious candidate human disease was investigated and excluded. That is a different quality of evidence from the structured silences most level 1 cells rest on, and it should be said in the brief, because "no evidence" reads as "nobody checked" unless the checking is described.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
Basis. ch51 51.3: "There is no evidence of L. intracellularis infection in humans", with the two negative studies described above. No human illness with this organism is described anywhere.
How this level was decided
Level 1, following C1. Pigs are not a source of human illness with this agent because it does not appear to infect people, and that has been looked for.
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. ch51 51.1: "PE is a common and important enteric disease of pigs worldwide. GLOBALLY, IT IS ESTIMATED THAT 96% OF FARM SITES ARE INFECTED, WITH APPROXIMATELY 30% OF WEANER-TO-FINISHER PIGS HAVING LESIONS of variable severity and duration." 51.4: "PE IS ENDEMIC IN DOMESTICATED SWINE HERDS and has also been described in feral swine populations worldwide... HIGH PREVALENCE of L. intracellularis is reported in commercial swine herds, mainly by serology and fecal PCR. Transmission is by the FECAL-ORAL ROUTE from infected pigs or contaminated environments to noninfected pigs. THE INFECTIOUS DOSE IS RELATIVELY LOW, and fecal excretion may be high in infected pigs." 51.10: "PARTIAL DEPOPULATION AND MEDICATION-BASED ERADICATION ATTEMPTS HAVE BEEN LARGELY UNSUCCESSFUL."
How this level was decided
Level 1, and the number settles it: 96% of farm sites worldwide are infected. There is no introduction event to prevent on 96 farms in 100, eradication attempts have largely failed, and the chapter treats hygiene as a way to reduce the level of infection rather than to exclude it. Scored level with Streptococcus suis, Glaesserella parasuis and Staphylococcus hyicus.
C4 Detection difficulty
Difficulty of recognizing and confirming infection
Laboratory-dependent: The presentation does not point to this disease specifically, but local or regional laboratories can confirm it with a validated assay once it is suspected
Basis. ch51 51.8: the differential for the chronic form runs to "endemic forms of coronaviruses, rotaviruses, Brachyspiral colitis, enteric salmonellosis, porcine circovirus-associated enteritis, enterotoxigenic colibacillosis, and nutritional diarrheas", and for the acute form to swine dysentery, gastric ulceration and hemorrhagic bowel syndrome. On confirmation: "PCR ASSAYS HAVE BEEN WIDELY USED TO CONFIRM L. INTRACELLULARIS DNA IN FECAL OR INTESTINAL MUCOSAL SAMPLES... The sensitivity of PCR techniques for L. intracellularis HAS INCREASED CONSIDERABLY over the last decade, mainly due to the development of REAL-TIME ASSAYS, INCLUDING COMMERCIAL KITS WITH MULTIPLE SEQUENCE TARGETS... Many PCR assays can detect as low as 100 organisms/g of feces." Immunohistochemistry is "THE GOLD STANDARD for specific identification of the bacterium in PE lesions". The trap: "BECAUSE OF THIS HIGH SENSITIVITY, THE MERE DEMONSTRATION OF L. INTRACELLULARIS IN FECES BY PCR MAY NOT INDICATE ECONOMICALLY SIGNIFICANT PE AT A HERD LEVEL."
How this level was decided
Level 2. Diarrhoea and poor growth in weaned pigs raise eight or nine agents and the chapter lists them, so it is not level 1; and confirmation is a commercial real-time PCR panel at any regional diagnostic laboratory, which is the level 2 label. NOTE THE INTERPRETIVE PROBLEM, which is the real difficulty here and is the mirror of the assay being good: at 96% site prevalence and 100 organisms per gram of detection, a positive PCR is close to expected, and the chapter says so. Establishing that this agent is causing THIS herd's problem needs serial sampling correlated against growth and feed conversion records, not a single test.
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. ch51 51.1: "Mild-to-severe diarrhea and weight loss are the major clinical signs... SUBCLINICAL INFECTION (I.E. LACKING DIARRHEA) IS COMMON in which infected pigs have less extensive lesions that are associated with A COMMENSURATE REDUCTION IN GROWTH RATES... Economic losses due to PE have been estimated from its negative impacts on SLAUGHTER WEIGHT, FEED CONVERSION EFFICIENCY, AND SPACE UTILIZATION, as well as breeding problems and morbidity and mortality effects, TOTALING FROM US$1 TO US$5 PER AFFECTED GROWING PIG. THE IMPACT IS LIKELY HIGHER SINCE ESTIMATES ARE BASED ON CLINICAL CASES AND DO NOT INCLUDE SUBCLINICAL CASES." The acute form, PHE, "may be associated with bloody diarrhea and HIGH MORTALITY"; 30% of weaner-to-finisher pigs carry lesions.
How this level was decided
Level 3, and it is one of the better-evidenced C5 cells in the register because the chapter gives a per-pig dollar range rather than an adjective. One to five dollars per affected growing pig, on 30% of weaner-to-finisher pigs, at 96% site prevalence, plus an acute haemorrhagic form with high mortality in breeding stock -- that is a measurable, continuous increase in cost of production absorbed within normal farm operations, which is the level 3 label including its endemic-disease clause. NOT LEVEL 4: the industry runs on this agent being present, and the chapter's own framing is loss of performance rather than loss of viability. The comparison worth making is PRRSV, scored level 3 at $5.70 per pig placed -- the same order of magnitude, the same answer.
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, no impact on markets"
Basis. PE is endemic in US swine herds at an estimated 96% of farm sites globally (ch51 51.1), and no trade measure, movement restriction or consumer response to a proliferative enteropathy diagnosis is recorded anywhere in the chapter.
How this level was decided
INFERRED. Level 1 under the standing note SCORING/market_impact: an agent present on almost every farm and routinely diagnosed in US pigs, with no market move ever observed.
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. ch51 51.10: "OVERALL, MACROLIDES AND PLEUROMUTILINS ARE THE MOST EFFECTIVE ANTIBIOTICS, WHEN GIVEN AT AN ADEQUATE DOSAGE RATE per kilogram of body weight... IN THE UNITED STATES, QUINOXALINES (SUCH AS CARBADOX) ARE ALSO AVAILABLE AND EFFECTIVE. ACQUIRED RESISTANCE BY L. INTRACELLULARIS TO THESE ACTIVE DRUG GROUPS HAS NOT BEEN DEMONSTRATED... APPARENT MEDICATION FAILURES WITH ANTIMICROBIALS KNOWN TO BE EFFECTIVE ARE MOST LIKELY DUE TO SUB-THERAPEUTIC DOSAGES." A preferred protocol is given: "tiamulin (120 ppm), tylosin (100 ppm), or tylvalosin (100 ppm) for 14 days."
How this level was decided
Level 1, and the label test is satisfied on wording you supplied yourself. Your tiamulin ruling of 2026-09-02 quoted the US label: "For control of porcine proliferative enteropathies (ileitis) ASSOCIATED WITH LAWSONIA INTRACELLULARIS..." -- the species is named on a US swine label, which is the first half of your rule and gives level 1 outright. The efficacy evidence agrees rather than pulling against it, which is what distinguishes this from Actinobacillus pleuropneumoniae at level 2: no acquired resistance has ever been demonstrated, and the chapter attributes apparent failures to underdosing rather than to the drug. NOTE THE ONE LIMIT, which does not reach the level: medication of breeding stock is "NOT LIKELY TO ELIMINATE THE INFECTION". Level 1 asks whether treatment improves outcomes, not whether it sterilises the herd.
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. ch51 51.10: "A MODIFIED LIVE VACCINE HAS BEEN WIDELY USED WITH DEMONSTRATED EFFECTIVENESS IN PREVENTING PE. IT HAS PROVIDED PROTECTION AGAINST SUBSEQUENT CHALLENGE WITH VIRULENT HETEROLOGOUS L. INTRACELLULARIS when administrated either by individual oral drench or drinking water delivery to a group of pigs (Kroll et al. 2004). VACCINATED ANIMALS SHOWED REDUCED PE LESIONS AND FECAL SHEDDING of L. intracellularis along with better cell-mediated immune responses upon challenge."
How this level was decided
Level 1, and it is the worked example at this level. The first half of the label is met without qualification: an effective vaccine is widely available in the US, it has demonstrated effectiveness, and -- unusually for a bacterial vaccine in this register -- it protects against HETEROLOGOUS challenge, which is the clause that holds Glaesserella parasuis and Actinobacillus pleuropneumoniae at level 2. Group water delivery makes it practical at scale. This is not the "not needed" half of level 1; it is the vaccine-exists-and-works half.
Levels and evidence are generated from data/assignments/lawsonia_intracellularis.yml; the overview is authored in data/overviews/lawsonia_intracellularis.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.