Sarcocystis spp.
LEVELS: Sometimes occurs; Mild; Housing alone keeps it out; Laboratory-dependent; Negligible; Negligible; Little; Available, or not needed
| Register id | sarcocystis_spp |
| Type | parasite |
| Scientific name | Sarcocystis |
| NCBI taxid | 5812 |
| Evidence | 2 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Sarcocystis species are protozoa that cycle between a predator and its prey: the definitive host sheds infective stages in its faeces, and the intermediate host — here the pig — forms cysts in muscle. Three species use pigs this way, and which one matters depends on the definitive host. Sarcocystis miescheriana runs a pig-dog cycle and is the only species found in the United States. S. porcifelis uses the cat. S. suihominis uses the human, and people acquire it by eating undercooked pork. In the pig, none of them causes anything: there are no reports of naturally occurring clinical disease due to Sarcocystis infection in swine. The cysts sit in muscle, most often in the heart, diaphragm and oesophagus. Infection tracks exposure to the ground and to definitive hosts — 3-18% of US breeding sows raised outdoors and 32% of US wild swine are infected — and confinement removes it. There is no treatment and no vaccine, and none is needed for the pig's sake; the relevant control is on the human side, in cooking.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c1l3, definitely can end up in humans but rarely from domestic pigs, more often noncommercial or feral pig sources"
Basis. ch60 60.3: "Three species use pigs as the intermediate host and form tissue cysts (sarcocysts) in the pig muscles. Sarcocystis miescheriana has a pig-dog life cycle and is the only species found in the United States. The other species are S. suihominis, which uses the human as the definitive host, and S. porcifelis, which uses the cat." CFSPH 2020 records S. suihominis acquired by people eating undercooked pork.
How this level was decided
INFERRED, AND FLAGGED ON A DISTRIBUTION QUESTION. S. suihominis is a pig-to-human foodborne parasite whose definitive host is the person eating the pork, with cooking as the control point -- squarely level 3. But the chapter says S. miescheriana, whose cycle runs pig to dog, "is the only species found in the United States", and the general rule says to score today's US reality where a criterion asks what is present. Scored level 3 because the register entry is Sarcocystis spp. and S. suihominis is within it, and because the general rule also says to score as the agent would apply if it WERE present. If Eric prefers the entry scored on the US species alone, this is level 1 -- S. miescheriana cannot infect a person.
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, mild disease in humans"
Basis. Neither ch60 60.3 nor the CFSPH factsheet describes the clinical course of human intestinal sarcocystosis. ch60 60.3: "There are no reports of naturally occurring clinical disease due to Sarcocystis infection in swine."
How this level was decided
INFERRED, and thinly. Human infection with S. suihominis is an intestinal sarcocystosis producing self-limiting nausea and diarrhoea after eating raw or undercooked pork. Usually mild with serious disease rare is level 2. Neither document in the folder characterises it, so this rests on the shape of the parasite rather than on evidence held. FLAGGED alongside C1 -- if that cell goes to level 1 on the US-distribution argument, this one follows.
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. ch60 60.3: "Dogs excrete infective stages (sporocysts) in their feces." The other two species use the human and the cat as definitive hosts. "Surveys indicate that 3-18% of commercial breeding sows raised outdoors and 32% of wild swine examined in the United States have Sarcocystis infection."
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 too: "3-18% of commercial breeding sows raised OUTDOORS and 32% of wild swine examined in the United States have Sarcocystis infection."
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 under the standing note SCORING/introduction_risk. The test is where the contamination came from, and a pig cannot produce it -- the infective sporocyst is shed by a dog, a cat or a person, never by another pig. Not raising pigs on dirt does not exclude the agent while a farm dog is defecating in the yard. The 32% figure in US wild swine adds a second reservoir the industry does not control.
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, testing is available but confirmation can be laboratory dependent"
Basis. ch60 60.3: "There are no reports of naturally occurring clinical disease due to Sarcocystis infection in swine." Sarcocysts form in pig muscle and are found on examination. CFSPH 2020 records that in pigs and cattle "sarcocysts are found most often in the myocardium, diaphragm and esophagus".
How this level was decided
INFERRED. No clinical disease means nothing prompts a test, so level 1 is out. The finding is a sarcocyst in muscle at slaughter or necropsy, identified on histopathology, which is regional veterinary diagnostic laboratory work. Level 2. The inference is that species-level identification, which the folder does not describe a method for, is not what a diagnosis here requires.
C5 Production cost
Financial impact on the infected farm's cost of production
Negligible: No measurable effect on cost of production
Basis. ch60 60.3: "There are no reports of naturally occurring clinical disease due to Sarcocystis infection in swine (Dubey et al. 1989, 2016)."
How this level was decided
The chapter states it directly and cites nearly thirty years of literature for it. No clinical disease means no measurable effect on cost of production. 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, no evidence the market would react to a diagnosis"
Basis. Section 60.3 records no trade measure, movement control or consumer response. Sarcocystis is present in 3-18% of outdoor-raised US breeding sows and 32% of US wild swine without regulatory consequence.
How this level was decided
INFERRED. An agent already this prevalent in US pigs with no market response on record scores level 1 under the standing note SCORING/market_impact.
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. ch60 60.3 describes no treatment. "There are no reports of naturally occurring clinical disease due to Sarcocystis infection in swine."
How this level was decided
No treatment exists and none is needed, on an explicit statement that the agent causes no natural clinical disease in this species. Second clause of level 1, and the standing note SCORING/treatment_potential puts it there directly -- there is no imperative to treat.
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 for a vaccine"
Basis. No vaccine is described for Sarcocystis in swine in ch60 60.3 or in the CFSPH factsheet.
How this level was decided
INFERRED. No vaccine exists and none is warranted for a parasite that causes no natural clinical disease in pigs. Level 1 on the second clause.
Levels and evidence are generated from data/assignments/sarcocystis_spp.yml; the overview is authored in data/overviews/sarcocystis_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.