Entamoeba spp.
LEVELS: Highly unlikely; Mild; Housing alone keeps it out; Laboratory-dependent; Minor; Negligible; Some; Available, or not needed
| Register id | entamoeba_spp |
| Type | parasite |
| Scientific name | Entamoeba |
| NCBI taxid | 5758 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
This entry covers the Entamoeba amoebae of pigs as one unit — chiefly E. polecki and E. suis, with E. histolytica named because it is the species that matters in people. Eric grouped them on the view that all can show up in humans and vice versa but all are minor players, and the chapter supports that: swine are not a significant reservoir for E. histolytica, the most pathogenic human species. E. suis appears to have a restricted host range; E. polecki has four subtypes that have also been found in people and other hosts, though little is known about its disease ecology. In pigs the two porcine species are associated with chronic diarrhoea, and a Japanese study linked E. polecki to chronic diarrhoea and poor growth in pigs of 50 to 70 days old. Beyond that the picture is largely blank: the prevalence of these parasites in the US swine population is not known, no transmission route is described, and there is no treatment and no vaccine.
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. ch60 60.5.3: "Swine are not a significant reservoir for Entamoeba histolytica, the most pathogenic species in humans. Pigs are hosts of two Entamoeba porcine species, E. polecki and E. suis... Entamoeba suis appears to have a restricted host range, while E. polecki four subtypes (ST1-ST4) have also been found in humans and other hosts. This amoeba also infects humans, but little is known about the disease ecology of this parasite."
How this level was decided
MOVED L2 -> L1, re-read 2026-09-04 AGAINST THE REWORDED LABELS. ch60 60.5.3 rules out the pathogenic species first -- "Swine are not a significant reservoir for Entamoeba histolytica" -- and of what remains says "little is known about the disease ecology of this parasite". No human case is attributed to a pig.
PREVIOUS ANSWER, kept because the evidence behind it has not changed, only the level boundary: Level 2. The chapter rules out the obvious worry first -- pigs are not a significant reservoir for E. histolytica -- and what remains is E. polecki, whose subtypes are found in both pigs and humans. That makes pig-to-human transmission plausible, but the chapter says outright that little is known about the disease ecology, so it is not a documented pig-sourced infection, and no control point in pork production addresses it. Both clauses of level 2. The chapter places Entamoeba under "Potentially Transmissible to Humans", and potentially is again the operative word.
C2 Zoonotic impact
Severity of human illness caused by the agent
Mild: Human illness is usually mild and self-limiting, and serious disease occurs only rarely
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c2l2, this sits somewhere between l2 and l3 but given its rare occurrence as a zoonosis related to pigs (as opposesd to other sources), we will rate it l2"
Basis. ch60 60.5.3 does not describe human disease caused by E. polecki: "This amoeba also infects humans, but little is known about the disease ecology of this parasite." It states only that swine are not a significant reservoir for E. histolytica, "the most pathogenic species in humans".
How this level was decided
INFERRED, and thinly -- the folder says nothing about the human clinical course. Human E. polecki infection is generally asymptomatic or a mild non-dysenteric diarrhoea; the amoeba that causes severe invasive disease is E. histolytica, which the chapter explicitly separates from pigs. Usually mild with serious disease rare is level 2. FLAGGED: level 1 is defensible if the entry is read as scoring only what pigs demonstrably transmit, since no pig-sourced human illness is on record here.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c3l3, I think the evidence suggests the organism really only ends up in pigs if they have contact with contaminated human effluent. In some ways this makes it an l4 (reservoier other than pigs) but exposure is also pretty straightforward to manage. Again, might revisit this." [RENUMBERED level 3 to 2, from_level 3 to 2 on 2026-09-01 when C3 went from four levels to five. The words above are exactly as recorded and the decision is unchanged -- only the number beside it moved, because the scale did. 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.]
Basis. ch60 60.5.3: "Amoeba in the genus Entamoeba have been reported as pigs in various parts of the world. The prevalence of these parasites in the US swine population is not known." No transmission route is described in the section. Chapter 60 60.5 groups Entamoeba with the other faecal-oral protozoa of the large intestine.
How this level was decided
MOVED L3 -> L2 on 2026-09-01 by the five-level rework. You ruled this L3 under the four-level ladder while saying "In some ways this makes it an l4 (reservoir other than pigs) but exposure is also pretty straightforward to manage. Again, might revisit this." The five-level ladder is the revisit: keeping pigs out of contact with human effluent is a housing and siting matter rather than a running biosecurity program, so this is L2. Your ruling is renumbered, not revised. 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.
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. "c4l2, routine fecal diagnostics should locate and identify the pathogen"
Basis. ch60 60.5.3: "A study in Japan indicates that E. polecki is associated with chronic diarrhea and poor growth in young (50- to 70-day-old) pigs (Matsubayashi et al. 2015)." "The prevalence of these parasites in the US swine population is not known." "E. polecki four subtypes (ST1-ST4)" are distinguished, which is molecular work.
How this level was decided
INFERRED. Chronic diarrhoea and poor growth in nursery pigs has a long differential and points nowhere in particular, so level 1 is out. Finding amoebic trophozoites or cysts on faecal examination is routine local laboratory work, which puts this at level 2. NOTE: separating E. polecki from E. suis, and subtyping it, needs molecular methods -- but the register entry is the genus, so that is not what a diagnosis here requires.
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. ch60 60.5.3: "Pigs are hosts of two Entamoeba porcine species, E. polecki and E. suis, that are associated with chronic diarrhea." "A study in Japan indicates that E. polecki is associated with chronic diarrhea and poor growth in young (50- to 70-day-old) pigs (Matsubayashi et al. 2015)." "The prevalence of these parasites in the US swine population is not known."
How this level was decided
Level 2. There is a real production effect on the record -- chronic diarrhoea and poor growth in nursery pigs, which is exactly where feed conversion is bought and lost. What holds it to level 2 rather than 3 is that it rests on a single study in one country, the association is not shown to be causal, and US prevalence is unknown, so no herd-level burden can be claimed. Small losses. Note this is the one entry in section 60.5 that is NOT scored level 1 here: Giardia and B. coli both carry explicit statements of no clinical association, and this one carries the opposite.
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, no evidence to suggest diagnosis would have an effect on markets"
Basis. Section 60.5.3 records no trade measure, movement control or consumer response.
How this level was decided
INFERRED. A poorly characterised enteric amoeba with no regulatory status and no established zoonotic transmission from pigs has no route to pork supply or demand. Level 1.
C7 Treatment potential
Potential for treatment to improve outcomes
Some: Treatment exists but is inconsistent, requires extralabel use, or works only in some circumstances
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c7l2, there are antiprotozoals available extralabel though in many cases, in pigs the infection will be self limiting"
Basis. ch60 60.5.3 describes no treatment. The chapter records the disease it would treat: "E. polecki is associated with chronic diarrhea and poor growth in young (50- to 70-day-old) pigs".
How this level was decided
INFERRED. No swine treatment is described and no US-labelled product exists for amoebiasis in pigs; the nitroimidazoles that treat amoebiasis in other species are prohibited in US food animals, so that route is closed rather than merely extralabel. Under the standing note SCORING/treatment_potential this would be level 2 for extralabel use, but here the honest reading is that treatment is unavailable. Scored level 2 rather than 3 because the outcome to be improved is modest -- one study, unknown US prevalence -- so the gain from a treatment is not established. FLAGGED as a judgment between 2 and 3.
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. "c8l1, no clinical or market imperative to develo a vaccine"
Basis. No vaccine is described for Entamoeba in swine in ch60 60.5.3. "The prevalence of these parasites in the US swine population is not known."
How this level was decided
INFERRED. No vaccine exists, and under the reworded criterion the question is whether one is warranted. With US prevalence unknown and the clinical association resting on a single study, the disease does not clinically or economically justify vaccinating on present evidence. Level 1 on the second clause. NOTE: this is a level 1 recording an absence of demonstrated need, not a level 1 recording that the problem is solved -- if the Japanese finding held in US herds, this cell would move.
Levels and evidence are generated from data/assignments/entamoeba_spp.yml; the overview is authored in data/overviews/entamoeba_spp.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.