Trichinellosis
LEVELS: Sometimes occurs; Moderate; Housing alone keeps it out; Laboratory-dependent; Negligible; Negligible; Little; Available, or not needed
| Register id | trichinella_spiralis |
| Type | parasite |
| Scientific name | Trichinella spiralis |
| NCBI taxid | 6334 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Trichinella spiralis is the swine-adapted species of a genus of zoonotic nematodes whose larvae encyst in muscle. In the pig the infection is largely invisible — the intestinal adults can cause enteritis but this is not usually seen clinically, growth may be slightly reduced, and once the larval nurse cells are complete even that resolves. Its entire significance is as a foodborne risk to people, historically through pork and especially ground pork and sausage, since one infected carcass can be distributed through many products. That risk has been all but eliminated in commercial US pork: prevalence has run at 0.1-0.3% since the mid-twentieth century, human cases fell from about 450 a year in 1947 to around a dozen fifty years later, and most recent cases follow poorly cooked wild game rather than pork. Vigilance still matters for pasture-raised pigs, because rats and wildlife maintain the parasite and pigs acquire it by tail-biting, scavenging carcasses or eating uncooked meat waste. There is no treatment and no vaccine — control is entirely a matter of preventing pigs from eating meat, supported by the voluntary National Trichinae Certification Program. Cooking pork to 63 degrees C kills the larvae; salt-curing does not reliably do so.
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. ch61 61.2.3.3: "Trichinella are zoonotic, infecting humans as well as other mammals. The source of Trichinella varies but can include pork products. Ground pork or sausage is particularly of concern because a single infected carcass may find its way into numerous sausages." "Trichinella larvae cooked to a uniform temperature of 60 C are not infective; therefore, the US Department of Agriculture recommends that fresh pork be cooked to an internal temperature of 63 C." "Salt-curing does not reliably kill larval Trichinella, so cured products should be cooked."
How this level was decided
The classic level 3. Pork is a named human source, and the chapter enumerates the control points that interrupt it -- cooking to a specified core temperature, freezing at specified time and temperature, prohibition of raw garbage feeding, and the voluntary National Trichinae Certification Program. Transmission follows their failure, and the chapter names the specific failure mode: salt-curing does not work, so cured products slip past a control people believe in.
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, still considered to have moderate severity in humans though annual case load is very low and exclusively related to eating pork from feral pigs"
Basis. ch61 61.2.3.3 records the US human case count falling "from 450 cases per year in 1947 to about 12 cases per year 50 years later", and that recent cases more often follow "ingestion of poorly cooked wild game meat". It does not describe the clinical course in people.
How this level was decided
INFERRED -- the chapter counts human cases but does not characterise them. Human trichinellosis is a systemic illness of fever, myalgia and periorbital oedema that commonly brings people to medical attention, with myocarditis and neurological involvement in heavy infections and death uncommon. Clinically important illness commonly needing treatment, with death or permanent disability uncommon, is level 3. A folder document on human trichinellosis would settle this.
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. ch61 61.2.3.3: "T. spiralis has a global distribution, is the swine-adapted species, and is often detected in rats." "Examples of transmission opportunities within swine herds include tail-biting, scavenging (rats, raccoons, etc.), and consumption of garbage containing uncooked meat." "Trichinella is still present at a low level in swine as well as in wildlife in some regions, which is justification for continued vigilance, particularly among pasture-raised pigs."
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. rats, raccoons, wildlife and garbage containing uncooked meat, and Eric had already written the clause: "prevalence of disease is so low in domestic pigs and EXCLUDING IT FROM FARMS IS EASY".
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. A US wildlife reservoir that the chapter names explicitly -- rats and raccoons around the buildings, and wildlife generally -- giving continuous opportunity for exposure wherever pigs can scavenge. Level 4. Confinement and rodent control suppress the exposure but do not remove the reservoir, and the chapter singles out pasture-raised pigs as the standing risk.
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. ch61 61.2.3.3: "Both of the two main methods for detecting muscle cysts are labor-intensive and lack sensitivity." "These techniques have been largely replaced by a serum enzyme-linked immunosorbent assay (ELISA) that detects pig antibodies directed at a larval secretory antigen." "False negative ELISA results can occur when low populations (<5 larvae/gram of muscle) of parasites are present." "Growth rates may be reduced, but the disease is often undetectable."
How this level was decided
Nothing in the live pig points at this infection -- the chapter says the disease is often undetectable -- so level 1 is out. Confirmation is a serum ELISA, a standard assay that regional laboratories and the certification programme run, which puts it at level 2 rather than level 3. NOTE: the ELISA misses light infections below five larvae per gram, so a negative does not clear a carcass, but that is a sensitivity limit on an available test rather than a referral requirement.
C5 Production cost
Financial impact on the infected farm's cost of production
Negligible: No measurable effect on cost of production
Basis. ch61 61.2.3.3: "The intestinal adults may be associated with enteritis, although this is not typically observed clinically." "Growth rates may be reduced, but the disease is often undetectable." "Once the development of the nurse cell is complete, clinical signs regress, and normal growth rates resume." "The incidence of swine trichinellosis in the United States has varied from 0.1 to 0.3% since the mid-twentieth century because the use of control measures... has practically eliminated trichinellosis in commercial pork."
How this level was decided
The chapter states both halves: the infection is clinically undetectable in the individual pig, and control measures have practically eliminated it from US commercial pork. Under the standing note SCORING/production_cost_impact this is scored on modern US production, where it does not occur at measurable cost. Level 1.
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 and well understood, diagnosis would not have a market impact"
Basis. ch61 61.2.3.3: US human cases have fallen to about 12 a year and are now more often traced to wild game than to pork. "In the United States, there is a voluntary National Trichinae Certification Program aimed at continued efforts to eliminate trichinellosis."
How this level was decided
INFERRED. Trichinella has been present in US swine at 0.1 to 0.3% throughout the period pork has traded normally, and no diagnosis has produced a market response -- which is the test set by the standing note SCORING/market_impact. NOTE, and it is the same shape as the MAC export-testing point: the Trichinae Certification Program is a standing trade arrangement rather than a disruption triggered by disease occurring, so it does not lift this level, but it is why someone might argue level 2.
C7 Treatment potential
Potential for treatment to improve outcomes
Little: Effective pathogen-directed treatment is available and works, or animals recover acceptably without it
INFERRED — reasoned, not stated. The evidence implies this level rather than stating it. The reasoning is below.
Corrected by Eric from L2 Some. Reason: "c7l1, prevalence of disease is so low in domestic pigs and excluding it from farms is easy, there is no imperative to develop a treatment for pigs"
Basis. No anthelmintic in ch61 61.7.2 is labelled or described as effective against Trichinella -- the labelled products cover Ascaris, Hyostrongylus, Oesophagostomum, Strongyloides, Metastrongylus, Stephanurus and Trichuris. Control is entirely preventive: "the elimination of feeding raw meat, scavenging, and cannibalism is effective in preventing the transmission of Trichinella."
How this level was decided
INFERRED, and scored on the precedent Eric set at mycobacterium_avium_complex, which is the same shape of problem. He wrote there: "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." Every clause of that applies here. Level 2. FLAGGED so he can confirm the precedent is being carried across the batch as he intended.
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, prevalence of disease is so low in domestic pigs and excluding it from farms is easy, there is no imperative to develop a vaccine for pigs"
Basis. Neither ch61 nor any folder document reports a Trichinella vaccine. ch61 61.2.3.3: control measures "have practically eliminated trichinellosis in commercial pork", with US incidence at 0.1 to 0.3%.
How this level was decided
INFERRED. No vaccine exists, but under the reworded criterion the question is whether one is warranted, and management has already achieved what a vaccine would deliver -- the chapter says commercial pork is practically free of it. Level 1 on the second clause. FLAGGED as a fair cell to argue: this is a serious zoonosis with trade sensitivity, and someone could reasonably say a vaccine would still be valuable insurance.
Levels and evidence are generated from data/assignments/trichinella_spiralis.yml; the overview is authored in data/overviews/trichinella_spiralis.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.