Taenia solium / Cysticercosis
LEVELS: Sometimes occurs; Severe; Housing alone keeps it out; Laboratory-dependent; Negligible; Negligible; Some; Available, or not needed
| Register id | taenia_solium_cysticercosis |
| Type | parasite |
| Scientific name | Taenia solium |
| NCBI taxid | 6204 |
| Evidence | 2 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Taenia solium is the pork tapeworm, and the pig's role in it is as the intermediate host: pigs swallow eggs shed in human faeces, and the larvae encyst as cysticerci in muscle. The pig itself shows no characteristic signs — cysts are found at slaughter, or occasionally by palpating the tongue. The cycle depends entirely on pigs having access to human faeces, so free-roaming pigs and pigs with access to domestic waste are the risk, and denying that access halts transmission. That is why the pig/human cycle is now absent or largely absent from developed countries, though occasional cases still occur around human tapeworm carriers. The consequences at the plant are graded: a few cysticerci can be trimmed out, several require the carcass to be cooked, and a heavy burden means condemnation; freezing also kills the cysts. The serious disease is in people. Humans are the definitive host of the adult tapeworm, but they can also become accidental intermediate hosts by swallowing eggs, and the cysticerci then favour the central nervous system — neurocysticercosis is a differential for cognitive dysfunction anywhere the parasite is endemic. Pigs are not normally treated, though oxfendazole and a commercially available swine vaccine have been used in trial control programmes in some countries.
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 61.6.1.3: "Viable Taenia solium cysticerci are infective for humans, so meat inspectors search for them regularly. If inspection reveals only a few cysticerci, they may be excised and discarded. Finding several organisms requires the entire carcass be cooked at 170 C for 30 minutes... finding a high number of cysticerci leads to condemnation of the entire carcass. Freezing cuts of pork is another method of killing cysticerci." CFSPH 2020: "Wild boar can be infected, but domestic pigs are more important due to their close association with humans."
How this level was decided
Level 3, and the control points are unusually explicit -- meat inspection with a graded response by cyst count, plus cooking and freezing specifications. Human infection follows when they fail. The pig is unambiguously the source: the cysticercus in pork becomes the adult tapeworm in the person who eats it.
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. ch61 61.6.1.3: "Besides acting as the definitive host for Taenia solium, humans can become accidental intermediate hosts after ingesting the eggs. In humans, the cysticerci have a predilection for the central nervous system; neurocysticercosis should be a differential for cognitive dysfunction in humans wherever T. solium is endemic."
How this level was decided
Level 4. Neurocysticercosis is the leading infectious cause of acquired epilepsy worldwide and carries a substantial risk of permanent neurological damage. NOTE ON THE ROUTE, because it matters for how this reads: the severe human syndrome follows ingestion of EGGS from human faeces, not of cysticerci from pork. Eating infected pork gives an intestinal tapeworm, which is mild -- but that carrier then sheds the eggs that cause neurocysticercosis in others. C2 scores the severity of illness the agent causes in people, and the agent causes 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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c3l4, i would like to over-riding the level definition a bit becayse excluding exposure to human effluent would be a part of normal farm biosecurity, and it would be easy to implement. However, we specifically say the RISK of exposure is unavoidable in L4 and I guess that is true in this case. I reluctantly agree but am not going to mull it over any longer." [RENUMBERED level 4 to 5, from_level 4 to 5 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.] RESCALED 2026-09-03, when C3 went from five levels to four and level 4 absorbed level 5. A ruling of his is never overturned by a scale change, so what is recorded here is the same judgment expressed on the new scale. AND THE ENTRY ALSO MOVED, on the pass Eric approved the same day: the whole old level 5 block was re-read against the exclusion test rather than the reservoir test, because twenty-one of those entries had been renumbered past the housing level on 2026-09-01 without being judged against it. See the entry justification for the reason this one moved. Recorded on the old scale as level 5, from_level 5.
Basis. ch61 61.6.1.2: "Risk factors for infection include pigs that are free-roaming and have access to domestic waste and human feces." 61.7.1: "denying pigs access to human fecal material is efficacious for halting the transmission of Taenia solium." CFSPH 2020: "Its pig/human cycle is now absent or mostly absent in many developed countries, though occasional cases of cysticercosis occur in and around human tapeworm carriers."
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. eggs from human faeces, and Eric had already written the level 2 clause on this entry while ruling C8: "typical biosecurity, indoor herds, and no contact with human effluent except in rare accidents". His level 5 ruling of 2026-08-28 was made against the FOUR-level scale, before the housing level existed.
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. INFERRED, AND THE LEVEL SET FITS THIS ENTRY BADLY -- flagged as a batch-level question. The source of infection is an infected human shedding eggs, which is outside the pig industry and is not something farm biosecurity can inspect for, so levels 2 and 3 are both wrong on their face: each says "the source is other pig herds". That leaves level 4, which is what I have scored. But level 4 says the reservoir gives CONTINUOUS opportunity for exposure, and in a confinement unit with sanitation the opportunity is nil -- the chapter says denying access to human faeces halts transmission outright. This is the recurring shape of the ch61 batch and it is set out in the batch note below.
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 61.6.1.2: "There are no characteristic clinical signs associated with cysticercosis. The presence of a cysticercus is revealed at necropsy or slaughter. Palpation of the tongue may reveal deeply seated cysts." "Several ELISA assays have been developed to detect Taenia antigens as well as anti-Taenia antibodies. These assays have been applied in humans but are not regularly used for surveillance in swine herds."
How this level was decided
No clinical signs at all in the live pig, so nothing prompts a diagnosis -- level 1 is out. What finds it is routine meat inspection, and confirmation is a squash preparation showing the rostellar hooklets, which any laboratory can do and which the chapter notes survive even caseation. Level 2. The swine ELISAs exist but are not used in surveillance, so they do not change the working answer.
C5 Production cost
Financial impact on the infected farm's cost of production
Negligible: No measurable effect on cost of production
Basis. CFSPH 2020: "Its pig/ human cycle is now absent or mostly absent in many developed countries." ch61 61.6.1: "Although once widespread in distribution, the infection is now limited by methods of human hygiene and cooking of pork." Where it does occur the cost is carcass condemnation or mandated cooking.
How this level was decided
Under the standing note SCORING/production_cost_impact this is scored on modern US production, where the pig-human cycle is essentially absent. A cost that is essentially never incurred is not a measurable increase in cost of production. Level 1. The condemnation cost is real but is a consequence of a cycle that US sanitation has already broken.
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, unlikely to be a whole-herd or multi-herd event and would therefore not affect markets, in the very unusual situation that it was diagnosed"
Basis. Neither document records a trade measure, movement standstill or consumer response following a cysticercosis finding. The response the chapter describes is carcass-level: excision, mandated cooking, or condemnation of that carcass.
How this level was decided
INFERRED. The entire regulatory response sits inside the plant and applies to the individual carcass, which is a farm cost rather than a market disruption -- the same distinction already accepted on ascaris_suum, whose C6 reads that liver condemnation "affects an individual carcass, not the pork or pig market". 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
Basis. ch61 61.6.1.3 states flatly: "Swine intermediate hosts are not treated; elimination of the life cycle is accomplished by sanitation, treatment for infected humans, and proper disposal of human feces." CFSPH 2020 contradicts it: "Some trial programs have also treated infected pigs with oxfendazole to eliminate cysticerci."
How this level was decided
Level 2, AND THIS IS A CELL THE CFSPH SHEET CHANGED. On the chapter alone the answer looked like level 3 or level 1 -- no treatment given, none discussed. The factsheet records that oxfendazole does eliminate cysticerci in pigs and has been used in trial programmes. So a pathogen-directed treatment exists and works, but it is programme-level rather than routine practice and is not a US labelled swine use. Treatment that exists but requires extralabel use and works only in some circumstances is level 2 word for word.
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, on the "not needed" clause rather than on availability. He wrote "c1l3" against this cell, which names C1 and cannot be applied to C8; the prose is entirely about the vaccine and begins "agree with assessment", so it is read as c8l1. His words: "agree with assessment but for a different reason. I don't think we actually know very much about the vaccine efficacy and it is not, and is unlikely to ever be, an important issue for US production (typical biosecurity, indoor herds, and no contact with human effluent except in rare accidents) so we will not have a need for the vaccine, regardless if it works or not"
Basis. CFSPH 2020: "Some trial programs have also treated infected pigs with oxfendazole to eliminate cysticerci and/or used experimental porcine T. solium vaccines... One swine vaccine is now commercially available in some countries." "Its pig/ human cycle is now absent or mostly absent in many developed countries."
How this level was decided
Level 1, and this entry is the sharpest test the reworded criterion has had. A commercial swine vaccine EXISTS -- but in some countries, not the US, so the availability clause of level 1 is not met and the old wording would have forced level 3. The second clause carries it instead: the US pig-human cycle is essentially absent, so there is no unmet need here to record. FLAGGED for Eric, because this is exactly the situation the rewording was built for and it is worth confirming it behaves as he intended. Note also that a vaccine existing elsewhere is evidence the target is tractable, which would matter if the cycle ever re-established here.
Levels and evidence are generated from data/assignments/taenia_solium_cysticercosis.yml; the overview is authored in data/overviews/taenia_solium_cysticercosis.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.