Hydatid Cyst Disease
LEVELS: Highly unlikely; Severe; Housing alone keeps it out; Laboratory-dependent; Negligible; Negligible; Some; Available, or not needed
| Register id | echinococcus_spp |
| Type | parasite |
| Scientific name | Echinococcus |
| NCBI taxid | 6209 |
| Evidence | 2 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Echinococcus tapeworms live as adults in carnivores, which shed eggs in their faeces; pigs, other herbivores and omnivores, and people, become intermediate hosts by swallowing those eggs, and the larvae develop into hydatid cysts in the liver and other organs. This entry is at genus level because it names no single species. In the pig the infection is silent — there are no clinical signs suggestive of hydatid disease, and it is found at necropsy or slaughter, where affected organs are condemned. Diagnosis can be awkward because many hydatids in pigs, especially those of E. granulosus, are sterile and contain none of the protoscolices normally used to identify them. Hydatid disease is uncommon in the United States, but sylvatic cycles in wildlife make it a permanent background threat. Where pigs roam free or offal is fed to dogs, it is both an economic and a public health problem, because people develop the same cysts; the multilocular cysts of E. multilocularis grow invasively and behave much like a tumour. No drug used in pigs is active against it and there is no vaccine — control is aimed at the carnivore host and at proper disposal of offal.
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. ch61 61.4.2: adult Echinococcus "occur worldwide in carnivores, and their larval cysts (hydatids) occur in various herbivores and omnivores, including humans and swine". "Egg-laden proglottids are shed into the environment via feces" -- by the definitive carnivore host. "When ingested by a carnivore, each protoscolex develops into an adult cestode." "In areas of the world where pigs are free-roaming or where offal is fed to carnivores, hydatid cyst disease is both an economic and a public health concern since humans can develop hydatids."
How this level was decided
Level 1, and the life cycle settles it. Humans acquire hydatid disease by ingesting eggs shed in CARNIVORE faeces, and they are a dead-end intermediate host exactly as the pig is. A cyst in pork cannot infect a person -- it would have to be eaten by a dog to continue the cycle. The pig is a parallel victim, not a source. This is the dead-end pattern Eric ruled on for chikungunya, where the framework scores pig-to-human only.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. REVIEWED ON C1_C2_RECLASSIFICATION.md, 2026-09-04, after the C1/C2 rewording that separated exposure from consequence. Eric marked up every moved cell and reversed his own earlier setting on twenty of the twenty-one: "In almost every case, I agreed with new opinion and reversed my old setting." HIS MARKUP HERE WAS "l4". Reverses the 2026-09-01 move to level 1, restoring the level HE HIMSELF RULED before the rescoping. Human hydatid disease requires surgery and can be fatal. C1 records separately that the eggs are shed in carnivore faeces, not by pigs.
Basis. ch61 61.4.2: multilocular hydatids of E. multilocularis "have a germinal layer on both the inner and outer surfaces, which are capable of producing a more invasive lesion similar to that of a neoplasm". Unilocular E. granulosus cysts enlarge in the liver and other organs. The chapter does not describe the human clinical course.
How this level was decided
RE-SCORED 2026-09-04. C2 now grades the severity of the illness the agent causes in a person, independent of how the person was exposed -- the 2026-09-01 pig-attribution reading is reversed, and C1 alone carries the source question. Returns to the level Eric himself ruled before the 2026-09-01 rescoping moved it to 1. Human hydatid disease requires surgery and can be fatal.
PREVIOUS ANSWER, written under the pig-attribution reading: MOVED L4 -> L1 on 2026-09-01. Human hydatid disease is consequential and Eric ruled it so, but a person acquires it by ingesting eggs shed in CARNIVORE faeces, not from a pig. The pig is an intermediate host carrying the cyst, the same dead end a person is, which is why C1 is level 1. Moved by the 2026-09-01 C2 rescoping, which Eric accepted: "i accept the c2_review changes". C2 now grades the severity of illness acquired FROM PIGS, so an entry whose pig is a dead-end host has no pig-attributable illness to grade. THE LEVEL MUST NOT BE READ AS A FINDING THAT THE AGENT IS MILD -- it records that pigs are not a source.
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 61.4.2: "Hydatid cyst disease is uncommon in the United States, but sylvatic cycles of the parasite mean that it is an ever-present threat."
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 shed by carnivores onto pasture and feed. An indoor herd off dirt never meets them.
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. The chapter names a US sylvatic cycle and calls it an ever-present threat, which is a wildlife reservoir outside the pig industry in the exact sense level 4 describes. Farm biosecurity cannot close a wild canid cycle. 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, the uncommon in the US, is straightforward diagnosis that should be warranted by the submission history"
Basis. ch61 61.4.2: "There are no clinical signs that imply hydatid cyst disease, and diagnosis is usually done at necropsy. Aspirates of hydatid cysts contain protoscolices that contain calcareous corpuscles and hooks. Histologically the brood capsules and protoscolices can also be identified. One challenge for diagnosis is that some hydatids developing in pigs, particularly those of E. granulosus, are sterile (e.g. contain no protoscolices), which makes for a more difficult diagnosis."
How this level was decided
No clinical signs in the live pig, so nothing prompts a diagnosis and level 1 is out. Cysts are found at slaughter or necropsy and confirmed by histopathology, which is regional laboratory work. Level 2. The sterile-cyst problem is a real interpretive difficulty -- a cyst without protoscolices is harder to attribute -- but it does not require referral.
C5 Production cost
Financial impact on the infected farm's cost of production
Negligible: No measurable effect on cost of production
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c5l1, disease is not usually significant in pigs and effluent management in modern production suggests risk of infection is low even if it were to enter the US"
Basis. ch61 61.4.2: "Hydatid cyst disease is uncommon in the United States." "There are no clinical signs that imply hydatid cyst disease." Where it occurs the cost is condemnation of affected organs at slaughter.
How this level was decided
INFERRED. The chapter reports no clinical disease in pigs and describes the condition as uncommon in the US. A subclinical infection that is uncommon and costs only the affected organ does not measurably move cost of production. Level 1 under the standing note SCORING/production_cost_impact.
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, there would be a response if this disease were detected in a US pig at slaughter, but the response would likely be contained only to that herd. The disease epidemiology does not support the likelihood of a multisite outbreak occurring"
Basis. Neither document records a trade measure, movement control or consumer response arising from hydatid cysts in pigs. The finding is handled as organ condemnation at the plant.
How this level was decided
INFERRED. Organ condemnation is a carcass-level cost, not a market event, following ascaris_suum. 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
INFERRED — reasoned, not stated. The evidence implies this level rather than stating it. The reasoning is below.
Corrected by Eric from L1 Little. Reason: "c7l2, there are extralabel treatments available that could be used if necessary in pigs"
Basis. No anthelmintic in ch61 61.7.2 is described as active against Echinococcus in the pig -- the labelled products are nematode drugs. ch61 61.4.2: "There are no clinical signs that imply hydatid cyst disease", and control is directed at the carnivore definitive host and at offal disposal rather than at the pig.
How this level was decided
INFERRED. C7 asks how much better the pig outcome would be with a treatment, and there is no adverse pig outcome to improve -- the infection is silent and uncommon, and the whole control effort is aimed at breaking the carnivore cycle rather than at curing pigs. The second clause of level 1 is satisfied. This differs from trichinella_spiralis, scored level 2, because there the infected carcass carries a food-safety consequence that a treatment would remove, whereas a hydatid in pork is harmless to the person who eats it.
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, in countries where human-pig transmission is a problem, the problem is related to effluent management, hygiene, and meat inspection/cooking - it is controllable without a vaccine. Vaccine would be useful in some situations but the final solution is management, not vaccine. Vaccine will not be useful as part of a response/control program in the US"
Basis. Neither document reports a vaccine for Echinococcus in swine. ch61 61.4.2: the disease is "uncommon in the United States" and produces no clinical signs in pigs.
How this level was decided
INFERRED. No swine vaccine is described, but under the reworded criterion the question is whether one is warranted, and an uncommon subclinical condition whose control properly targets the carnivore host does not justify vaccinating pigs. Level 1 on the second clause.
Levels and evidence are generated from data/assignments/echinococcus_spp.yml; the overview is authored in data/overviews/echinococcus_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.