Rhodococcus equi
LEVELS: Highly unlikely; Severe; Housing alone keeps it out; Laboratory-dependent; Minor; Negligible; Little; Available, or not needed
| Register id | rhodococcus_equi |
| Type | bacteria |
| Scientific name | Prescottella equi |
| NCBI taxid | 43767 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Rhodococcus equi — now formally Prescottella equi — infects pigs almost silently. Clinical disease is rare; what the organism produces is granulomatous inflammation of the lymph nodes of the head and neck, found only at slaughter, so diagnosis is a post-mortem matter. Its importance is entirely that those lesions look like tuberculosis. A Dutch survey of 15,900 cervical lymph nodes found granulomatous lesions in 0.75% of pigs, 44% of them containing R. equi, and each has to be distinguished from mycobacterial infection by culture or PCR before a meat inspection decision can be made. Pigs housed outdoors probably acquire it from the ground by ingesting faecally contaminated material; earthworms concentrate it above the level in the surrounding soil and may be a source. The chapter's own judgement is that the disease is not important enough in pigs to warrant antemortem diagnosis, treatment or dedicated preventive measures. R. equi is an increasingly recognised cause of necrotising pneumonia in immunocompromised people, with around 25% mortality, but pig-to-human and pork-to-human transmission is not documented.
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. "R. equi is also a cause of infection and mortality in immunocompromised humans but swine have not been associated with human infections." "Human isolates are similar to some pig strains; however, pig-to-human or pork-to-human transmission is not documented." "Rhodococcus equi is of importance to public health as a cause of granulomatous lesions in the cervical lymph nodes of pigs. These must be distinguished from those of tuberculosis... and are therefore of concern in meat inspection." (ch58 58.10.1)
How this level was decided
MOVED L2 -> L1, re-read 2026-09-04 AGAINST THE REWORDED LABELS. ch58 58.10.1 states it twice: "swine have not been associated with human infections" and "pig-to-human or pork-to-human transmission is not documented". The meat-inspection interest is in distinguishing its lesions from tuberculosis, not in preventing human infection.
PREVIOUS ANSWER, kept because the evidence behind it has not changed, only the level boundary: Level 2 rather than level 1, and the distinction is the chapter own. Human isolates resemble some pig strains, which makes a pig-to-human route plausible, but transmission from pigs or pork is explicitly not documented and nothing is done to prevent it -- both clauses of level 2. Compare klebsiella_pneumoniae, scored level 1 in this batch because the chapter states flatly that it is not a zoonotic agent. NOTE: the meat inspection interest in R. equi is about distinguishing its lesions from tuberculosis, not about preventing human infection, so it is not a control point in the C1 sense.
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. "R. equi can infect humans and is becoming more common as a cause of necrotizing pneumonia and chronic illness in immunocompromised humans, particularly in those suffering from HIV infections (Weinstock and Brown 2002). Infection results in high mortality, averaging 25%." (ch58 58.10.1)
How this level was decided
A stated average mortality of 25% in the human disease is a substantial risk of death, which is level 4. C2 applies that "even if human infections are uncommon", and level 4 here sits beside level 2 at C1 without contradiction -- the framework separates how likely infection is from how bad it is, which is the separation Eric accepted on chikungunya.
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. "Little is known of the epidemiology of R. equi infection in swine, but R. equi has been reported worldwide and may infect swine, cattle, deer, horses, sheep, goats, wild birds, and humans." "In swine housed outdoors, R. equi infection is likely to be acquired from the environment by ingestion of fecal-contaminated material." "The bacterium can be found in the gastrointestinal content of earthworms at concentrations greater than the surrounding soil, and thus they may be a source of infection." (ch58 58.10.1, 58.10.2)
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. the chapter keys it to housing itself: "in swine housed OUTDOORS, R. equi infection is likely to be acquired from the environment by ingestion of fecal-contaminated material."
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. Soil, earthworms and a host range spanning six other domestic and wild species put the reservoir firmly outside the pig industry and beyond herd biosecurity. Level 4.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "l2, straightforward to diagnose"
Basis. "Rhodococcus equi infection in swine is normally subclinical and has rarely been associated with clinical disease. The lesions of granulomatous lymphadenitis are detected only at slaughter." "Diagnosis is postmortem." "Microbiological identification of R. equi and rule-out of mycobacterial infection is necessary to confirm a diagnosis. Selective media (Makrai et al. 2005; Woolcock et al. 1979) improve the results of culture, as the creamy or pink-domed colonies of R. equi require 48 hours to reach a size of 2-4 mm. A quantitative PCR targeting the chromosomal gene choE and the virulence plasmid gene vapA can also be used." (ch58 58.10.3)
How this level was decided
Infection is silent in the live pig and the lesions surface only on the slaughter line, where they are indistinguishable from tuberculosis -- so nothing points at this agent clinically, ruling out level 1. Confirmation is selective culture at 48 hours or a qPCR, both within regional laboratory capability. Level 2. NOTE: the practical difficulty here is not the assay but that R. equi is cultured from lymph nodes without lesions in a quarter of pigs, so isolation alone does not confirm causation.
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
Basis. "Rhodococcus equi causes granulomatous lymphadenitis in the head and neck of the pig. Its major importance is that the lesions can be confused at slaughter with those of tuberculosis." "Komijn et al. (2007) examined 15,900 cervical lymph nodes for granulomatous lesions in the Netherlands and found them in 0.75% of pigs, with 44% of these lesions containing R. equi." "Rhodococcus equi-induced disease is not sufficiently important to necessitate antemortem diagnosis and treatment in swine or dedicated preventive measures." (ch58 58.10.1, 58.10.2, 58.10.4)
How this level was decided
The cost is trimming or condemnation of head and neck lymph nodes in a fraction of one percent of pigs, plus the diagnostic work of ruling out tuberculosis. The chapter judges the disease not important enough to warrant antemortem diagnosis, treatment or preventive measures, which is as close as it comes to saying the losses are small. Level 2 rather than level 1, because carcass trim and the tuberculosis rule-out are real if minor costs.
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, this is an exceedingly rare infection in pigs and would not be expected to cause any effect on markets as it is already known to be in the US"
Basis. The section describes a subclinical infection found at slaughter, explicitly not associated with human infection, and not warranting preventive measures. It records no trade measure, movement control, export restriction or consumer response.
How this level was decided
INFERRED. A subclinical lymph node lesion in under one percent of pigs, with no zoonotic route and no regulatory status, has no mechanism to move pork supply or demand. 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. "Rhodococcus equi-induced disease is not sufficiently important to necessitate antemortem diagnosis and treatment in swine or dedicated preventive measures." "Rhodococcus equi infection in swine is normally subclinical and has rarely been associated with clinical disease." (ch58 58.10.3, 58.10.4)
How this level was decided
C7 scores the size of the opportunity a treatment would create, and the chapter states there is not one -- the disease does not warrant treatment because pigs are not clinically affected. The second clause of level 1 is satisfied: animals recover acceptably without treatment. NOTE: this is scored differently from mycobacterium_avium_complex in the same batch, where lesions drive whole-carcass condemnation. Here the loss is confined to nodes that are trimmed, and the chapter itself rules treatment out.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED AT LEVEL 1. "c8l3, no vaccine for pigs exists nor is there any current motivation to develop or use one" Eric, 2026-08-28: "all seven to L1". Re-ruled after the C8 rewording of the same day. His 2026-08-27 words are unchanged and are quoted above in full -- what has moved is the level they map to. He wrote each of them to say that no vaccine is NEEDED here, and level 3 was then the only place a missing vaccine could go, so the reasoning and the level contradicted each other. The reworded level 1 holds exactly what he was describing: no vaccine exists, and the disease does not justify one. Recorded as a confirmation of the reworded pass rather than an override, because the pass now agrees with him.
Basis. ch58 58.10.4: "Rhodococcus equi-induced disease is not sufficiently important to necessitate antemortem diagnosis and treatment in swine or dedicated preventive measures." Eric, 2026-08-27: "no vaccine for pigs exists nor is there any current motivation to develop or use one".
How this level was decided
MOVED L3 -> L1 by the rewording, and the chapter states the test in its own words -- not sufficiently important to warrant dedicated preventive measures. A vaccine is a dedicated preventive measure. Level 1.
Levels and evidence are generated from data/assignments/rhodococcus_equi.yml; the overview is authored in data/overviews/rhodococcus_equi.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.