Whipworm
LEVELS: Rarely occurs; Mild; Housing alone keeps it out; Laboratory-dependent; Minor; Negligible; Little; Needed but not available
| Register id | trichuris_suis |
| Type | parasite |
| Scientific name | Trichuris suis |
| NCBI taxid | 68888 |
| Evidence | 2 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Trichuris suis, the whipworm, lives in the caecum and colon and has persisted as an important parasite even of pigs raised indoors in confinement — its eggs, like the roundworm's, remain viable in the environment for several years. Heavy infections ulcerate the gut lining, causing oedema, haemorrhage, diarrhoea, blood in the faeces and rectal prolapse. Much of the damage is done by larvae burrowing in the mucosa before adult worms are visible, which matters diagnostically because at that stage the lesions can be mistaken for swine dysentery or salmonellosis. Faecal examination is unreliable early on: the prepatent period is six to seven weeks and females lay sporadically, so false negatives are common, and the antigen tests developed for other species have not been shown to work for T. suis. Not every anthelmintic clears it — fenbendazole is one of the few reliably effective drugs, dichlorvos works, and doramectin's efficacy is variable. Its human counterpart T. trichiura has been found in pigs in tropical areas with poor sanitation, raising the possibility of transmission in the reverse direction, but no illness in a person has been attributed to T. suis from pigs.
C1 Zoonotic potential
Likelihood of transmission from pigs to humans
Rarely occurs: Human infection from pigs is plausible but has only rarely been reported, and specific control points are not commonly implemented to prevent 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. "c1l2, does rarely occur by accident and there is also some purposeful exposure of human as part of some immune therapies"
Basis. CFSPH 2019: "T. trichiura have been detected in the feces of some pigs, dogs and cats in tropical areas with poor sanitation, raising the possibility of reverse zoonoses", and it cites genetic analysis of T. suis and T. trichiura "recovered from humans and pigs in a sympatric setting in Uganda". ch61 61.2.4.1 addresses only the pig.
How this level was decided
RE-READ AND HELD AT L2 2026-09-04 AGAINST THE REWORDED LABELS. T. suis ova are used as a deliberate human therapeutic, which establishes that this pig parasite occupies a human gut, and the folder carries genetic work on T. suis and T. trichiura recovered from humans and pigs in a sympatric setting in Uganda.
PREVIOUS ANSWER, kept because the evidence behind it has not changed, only the level boundary: INFERRED. The direction the folder documents most clearly is the wrong one for C1 -- human T. trichiura turning up in pigs is a reverse zoonosis. What supports level 2 is the sympatric human-and-pig genetic work, plus the well-known use of T. suis ova as a deliberate human therapeutic, which together establish that this pig parasite can occupy a human gut. That makes pig-to-human transfer plausible and rarely reported, with nothing in pork production directed at preventing it. Both clauses of level 2.
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, low infection levels are inapparent and higher levels are mild"
Basis. Neither document reports clinical illness in a person attributed to T. suis acquired from pigs. CFSPH 2019 frames the pig-human overlap as a taxonomic and epidemiological question rather than a clinical one.
How this level was decided
INFERRED. T. suis in humans is characteristically transient and self-limiting -- the basis on which it has been given deliberately as a therapeutic -- and no folder document records serious human disease from it. Usually mild with serious disease rare is level 2. Level 1 is arguable if the human colonisations are read as carriage rather than infection.
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 61.2.4.1: "Eggs pass in the feces, and once outside the body, the first-stage infective larva develops within the egg in 3-4 weeks... Eggs can remain viable for several years in the environment." "Much like ascarids, whipworms have persisted as an important parasite of pigs raised in confinement facilities."
How this level was decided
MOVED L3 -> L2 on 2026-09-01. Eggs leave in pig faeces and re-infect from the ground years later, so the contamination is pig-origin throughout and the persistence is extreme. Extreme persistence in soil is not the same as an unblockable route: it makes the ground permanently unsafe and leaves the pig on slats untouched. 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. 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 61.2.4.1: "Much of this tissue damage is caused by the histotrophic larvae, before adults are grossly present and can be easily confused with lesions of swine dysentery or salmonellosis." "false negatives may occur due to sporadic egg-laying by females, as well as the long (6-7 week) prepatent period." "Commercial Trichuris antigen detection tests have been developed for use in other domestic animal species but their utility has not yet been proven for T. suis."
How this level was decided
Scored a level above ascaris_suum, which sits at level 1, and the chapter gives the reason. Ascariasis is diagnosed by prodigious egg output on routine flotation; whipworm is not -- egg-laying is sporadic, the prepatent period is six to seven weeks, and the clinical signs during that window mimic swine dysentery and salmonellosis. Flotation is still a local test, so this is level 2 rather than level 3, but the presentation does not point here and a negative does not clear the animal.
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
Basis. ch61 61.2.4: nodular worms and whipworms are "both very common, and both can lead to important clinical diseases". 61.2.4.1: "Heavy infections with Trichuris are associated with ulceration of the mucosa, mucosal edema, and hemorrhage... Clinical signs include diarrhea, hematochezia, and rectal prolapse." "whipworms have persisted as an important parasite of pigs raised in confinement facilities."
How this level was decided
Level 2, matching ascaris_suum, and for the same reason: this is one of the two helminths in the chapter that modern confinement has NOT removed, so the standing note SCORING/production_cost_impact does not zero it out the way it does the pasture parasites. Heavy infections cause real clinical disease including rectal prolapse, but the chapter frames the usual case as low populations causing minimal lesions. Measurable and manageable rather than substantial.
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
Basis. Neither document records a trade measure, movement control, export restriction or consumer response arising from whipworm. The parasite is non-reportable, endemic and diagnosed routinely.
How this level was decided
Level 1 under the standing note SCORING/market_impact: an agent already endemic in US herds and routinely diagnosed, with no historical evidence of any market response. Losses fall on the affected farm and are scored at C5.
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. ch61 61.7.2.2: "Fenbendazole products are labeled for the treatment of A. suum, Metastrongylus, Oesophagostomum, Hyostrongylus, Stephanurus, and Trichuris in the United States. It should be noted that fenbendazole is thought to be one of the few anthelmintics effective for the removal of Trichuris." 61.7.2.6: dichlorvos has "good efficacy against Ascaris, Oesophagostomum, Trichuris, and Hyostrongylus" and can be given in slow-release pellets "producing the desired removal of whipworms". 61.7.2.1: doramectin has "variable efficacy for Trichuris".
How this level was decided
Effective, US-labelled, pathogen-directed treatment exists, which is level 1. The chapter is careful that whipworm is harder to remove than most -- one of the few effective anthelmintics, and variable macrocyclic lactone efficacy -- but the criterion asks how much better outcomes would be if a treatment existed, and two effective labelled options do exist.
C8 Vaccine availability
Availability of effective vaccines or bacterins
Needed but not available: No effective vaccine is available in the US or has been developed, and the disease would justify vaccinating if one existed
Basis. Neither document reports a commercial or experimental whipworm vaccine. ch61 61.2.4: whipworms "can lead to important clinical diseases" and have "persisted as an important parasite of pigs raised in confinement facilities".
How this level was decided
Level 3 under the reworded criterion, matching ascaris_suum. Both tests are met: no vaccine exists, and the disease would justify one -- this is a common parasite causing clinical disease that has survived both confinement and decades of anthelmintic use. That is a genuine unmet need rather than a product nobody wants.
Levels and evidence are generated from data/assignments/trichuris_suis.yml; the overview is authored in data/overviews/trichuris_suis.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.