Nodular Worms
LEVELS: Highly unlikely; No human illness; Housing alone keeps it out; Laboratory-dependent; Minor; Negligible; Little; Available, or not needed
| Register id | oesophagostomum_spp |
| Type | parasite |
| Scientific name | Oesophagostomum |
| NCBI taxid | 52564 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
The nodular worms, genus Oesophagostomum, are among the commonest parasites of pigs, though less prevalent in animals raised indoors. The life cycle is direct: eggs pass in faeces, develop through two moults in the environment to an infective third-stage larva that keeps its old cuticle as a protective sheath, and are then swallowed. That sheath makes the larvae moderately resistant to environmental extremes and lets them survive several months or more. The adult worms in the large intestine cause little damage and few signs; the characteristic lesion is the nodule formed where larvae burrow and moult in the gut wall, usually a couple of millimetres across but larger in animals infected repeatedly. Diagnosis by faecal flotation is complicated because the eggs of Hyostrongylus and Globocephalus look much the same, so definitive identification means culturing larvae to the third stage; at necropsy the nodules must be distinguished from other causes of inflammation. It is the best-covered parasite in the reference chapter for treatment — avermectins, fenbendazole, levamisole, pyrantel, piperazine and dichlorvos all work — and pyrantel is commonly fed continuously to growing pigs to prevent it establishing.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c1l1, no evidence of human infection"
Basis. Section 61.2.4.2 covers nodular worms in full and makes no mention of human infection, foodborne risk or occupational exposure. Chapter 61 flags zoonotic potential wherever it exists -- for Gongylonema, Ascaris, Trichinella, Taenia, Fasciola, Echinococcus and Macracanthorhynchus -- and states explicitly where it does not, as for Globocephalus.
How this level was decided
INFERRED from a structured silence rather than a bare absence. This chapter is consistent about naming the human angle when there is one, and it names none here. The human Oesophagostomum species are primate parasites of West Africa, not the swine species. Level 1 is itself a statement about absence of evidence, which is what the folder supports.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c2l1, no evidence of human infection"
Basis. No human disease of any kind is described in 61.2.4.2.
How this level was decided
INFERRED, on the same structured silence as C1. C2 says to score level 1 whenever the agent does not cause disease in people.
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 61.2.4.2: "The life cycle is direct; eggs passed in feces develop into first-stage larvae that hatch from the egg and molt twice in the environment to produce an infective third-stage larva, which is ingested by swine. Infective larvae retain their last molted cuticle as a sheath so they are moderately resistant to environmental extremes and can survive for several months or more."
How this level was decided
MOVED L3 -> L2 on 2026-09-01. A direct life cycle, pig faeces to ground to pig, with sheathed larvae surviving months. Persistence in the environment is what made it look like level 3, but persistence is only a threat where pigs meet the environment. Scored under the 2026-09-01 C3 rework: level 2 is where the farm's own housing decision closes the route permanently, and an outdoor herd's exposure is a consequence of that production choice rather than a property of the agent. Eric: "accept being an outdoor herd itself is the biosecurity failure/risk, not the agent per se, and covers things like most gut parasites." Level 3 is reserved for routes no housing system blocks. NOTE: this cell has now moved twice, L4 to L3 on 2026-08-28 and L3 to L2 today. Both moves are the same correction applied further -- the reservoir was never outside the pig industry, and it was never beyond the reach of a housing decision. CONFIRMED AT L2 by the five-level rework later the same day. The four-level L2 had held two different amounts of work -- this case, where housing alone does it, and agents like progressive atrophic rhinitis that need a running biosecurity program and are equally excludable from an outdoor herd. Eric spotted it: the qualifier "but outdoor herds may still be exposed" is true here and false there. Those agents moved up to the new L3 and this one stayed, on a level that now says only what is true of it.
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 61.2.4.2: "Antemortem diagnosis of nodular worms depends on finding the eggs in fecal flotation. However, this is complicated by the fact that eggs of Hyostrongylus and Globocephalus resemble them. For definitive identification, larval culture to the L3 stage is needed." "At necropsy, the finding of nodules in the cecum and colon is suggestive but must be differentiated from other causes of inflammation, diverticulitis, or abscessed lymphoglandular complexes." "Adults cause minimal damage to the mucosa and do not cause much in the way of clinical signs."
How this level was decided
Scored a level above ascaris_suum for a reason the chapter gives directly: flotation finds a strongyle egg but cannot say which strongyle, and separating this genus from Hyostrongylus and Globocephalus needs larval culture to L3. There are also no clinical signs to prompt the test. Both are level 2 -- not recognised clinically, but confirmable at local level once someone looks.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c5l2, easy and inexpensive to control in settings where exposure may occur"
Basis. ch61 61.2.4: nodular worms and whipworms are "both very common, and both can lead to important clinical diseases". 61.2.4.2: "Adults cause minimal damage to the mucosa and do not cause much in the way of clinical signs. The migration and molting of larvae in the lamina propria cause the characteristic nodule, which is usually small (about 2 mm) but may be much larger, especially in animals with repeated infections." "common, although less prevalent in swine raised indoors".
How this level was decided
INFERRED -- no cost figure. The chapter calls the genus very common and capable of important clinical disease, but its own description of the lesion is minimal mucosal damage and few clinical signs. It is also the parasite most comprehensively covered by labelled anthelmintics, which caps what it can cost a farm that treats. Small losses rather than a measurable increase in cost of production. Level 2, matching ascaris_suum.
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, diagnosis will not trigger any effect on the market"
Basis. Section 61.2.4.2 records no trade measure, movement control, export restriction or consumer response. Nodular worms are non-reportable and endemic.
How this level was decided
INFERRED. An endemic, non-zoonotic gut nematode routinely controlled by in-feed anthelmintics has no route to pork supply or demand. Level 1, and the standing note SCORING/market_impact returns the same answer on an agent long present and routinely diagnosed in US herds.
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. Oesophagostomum is the most comprehensively covered parasite in ch61 61.7.2 -- labelled or described as controlled by avermectins and doramectin (adults and fourth stage larvae), fenbendazole, levamisole, pyrantel tartrate, piperazine and dichlorvos. 61.7.2.4: pyrantel is "most commonly used as a continuous dewormer for 30 days in starter and growing pigs as an aid in the prevention of larval migration and establishment of A. suum and Oesophagostomum".
How this level was decided
Six labelled or effective compounds across five drug classes, including in-feed prophylaxis. Effective pathogen-directed treatment is available and works, which is level 1 with nothing to qualify.
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 market imperative to develop a vaccine"
Basis. No vaccine for Oesophagostomum is described anywhere in ch61. The Control section addresses this genus entirely through sanitation, housing and anthelmintics.
How this level was decided
INFERRED. No vaccine exists, but the reworded criterion asks whether one is warranted, and a parasite causing minimal clinical disease and controlled by six labelled compounds does not justify developing one. Level 1 on the second clause. This is the same shape as the ch58 entries Eric re-ruled to level 1 on 2026-08-28.
Levels and evidence are generated from data/assignments/oesophagostomum_spp.yml; the overview is authored in data/overviews/oesophagostomum_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.