Hepatitis E Virus
LEVELS: Sometimes occurs; Severe; Already in the herd; Reference or research laboratory required; Negligible; Negligible; Little; Needed but not available
| Register id | hepatitis_e_virus |
| Type | virus |
| Scientific name | Hepatitis E virus |
| NCBI taxid | 291484 |
| Evidence | 2 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
Hepatitis E virus is on this register for what it does to people, not to pigs. Experimentally infected pigs stay clinically normal; the changes are microscopic liver inflammation and mildly enlarged lymph nodes, with no effect on reproduction. The infection is ubiquitous in pigs worldwide regardless of whether the virus is common in the local human population, and it follows a predictable pattern: piglets are protected by maternal antibody, become infected at two to three months as that wanes, and are seropositive by three months. HEV RNA was found in 6.3% of market-weight pigs sampled at 25 US slaughterhouses across ten states. The human side is what matters. People acquire it occupationally and by eating undercooked pork — US swine veterinarians are about 1.5 times more likely than other blood donors to carry antibody, and North Carolina swine workers were four times more likely than controls — and around 11% of pig liver sold in US grocery stores tested positive, with the positive samples proving infectious. Mortality in people is generally under 1% but reaches 30% in pregnant women, and chronic hepatitis E in transplant recipients is almost exclusively caused by the swine-origin genotypes. A joint FAO/WHO expert committee ranked HEV among the top three foodborne viral pathogens, with pork named as a globally important pathogen-commodity pairing. A human vaccine is licensed in China; there is none for pigs.
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, agree with assessment"
Basis. ch41 41.4.1: "The risks associated with acquiring swine HEVs include occupational exposure to infected pigs and consumption of undercooked pork or pork products." "swine veterinarians in the United States were 1.51 times more likely to be positive for anti-HEV antibodies than other blood donors", and North Carolina swine workers had "a 4.5-fold higher HEV antibody prevalence rate (10.9%) than control subjects (2.4%)". "Approximately 2% of the pig liver sold in grocery stores in Japan and 11% in the United States tested positive for swine HEV RNA, and positive pig liver from the grocery stores in the United States was infectious." "The infectivity of swine HEV present in commercial pig livers is inactivated by adequate cooking (e.g. frying or boiling for 5 minutes)." shic_hev: "HEV is zoonotic... Pigs are the most important animal reservoir for genotypes capable of infecting people." "HEV-3 and HEV-4 are zoonotic with swine serving as the reservoir host." "Heating pork products to an internal temperature of 71C for 20 minutes is required to completely inactivate HEV."
How this level was decided
Level 3, and the strongest-evidenced C1 in the register so far. Both routes are quantified: a measured occupational excess in the people who handle pigs, and 11% of US retail pig liver carrying infectious virus. The control point is named and works -- adequate cooking inactivates it. Transmission follows its failure. FLAGGED FOR ERIC AS ARGUABLY LEVEL 4: the occupational route has no control point directed at it at all. Nobody wears respiratory protection or changes practice for HEV, and swine veterinarians are seroconverting anyway, which is the level 4 test -- transmission occurring while control points are intact, because for that route there are none. Scored 3 because the dominant documented route is foodborne and cooking closes it. Level 3 confirmed and strongly supported: pigs are named as the most important animal reservoir for the human-infecting genotypes, and the control point is cooking pork properly -- transmission occurring after failure of a control point, which is the level 3 label.
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. ch41 41.4.1: "The mortality associated with HEV infection in humans is generally low (<1%) but can be up to 30% in pregnant women." "Chronic hepatitis E cases in organ transplant recipients are almost exclusively linked to HEV-3 and HEV-4 strains of swine origin." shic_hev: "The severity of infection in humans varies from subclinical to fulminant hepatitis, along with reproductive effects."
How this level was decided
Level 4. Case fatality reaching 30% in pregnancy is a substantial risk of life-threatening illness on its own, and the chronic hepatitis in transplant recipients -- which the chapter attributes almost exclusively to the swine-origin genotypes -- is permanent harm in the population most exposed to it through a different route. C2 applies level 4 "even if human infections are uncommon", and here they are not uncommon either. Level 4 held. Fulminant hepatitis and reproductive effects in pregnancy carry a substantial risk of life-threatening illness, which the level 4 label allows even where most infections are subclinical.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Already in the herd: Present in most herds, or carried by pigs themselves, so there is no introduction event to prevent
Basis. ch41 41.4.2: "HEV infection is ubiquitous in pigs worldwide, regardless of whether HEV is endemic in the respective human population." "HEV seroprevalence in pigs is age-dependent: most pigs younger than 2 months of age are seronegative, whereas most pigs older than 3 months of age are seropositive. The infection generally occurs at 2-3 months of age, shortly after maternally derived antibodies wane." 41.4.1: "HEV RNA was detected in 6.3% of serum samples from market-weight pigs at 25 slaughterhouses in 10 US states." shic_hev: "In the United States, 80 to 100% of commercial swine farms show evidence of infection with HEV." "Most pigs become infected with HEV once maternal antibody wanes." "HEV is ubiquitous and difficult to detect."
How this level was decided
Ubiquitous worldwide and cycling through each group of pigs as maternal antibody wanes, with 6.3% of US market pigs viraemic at slaughter. There is no introduction event to prevent. Level 1. Level 1 confirmed about as decisively as any cell in this round -- 80 to 100% of US commercial farms show evidence of infection.
C4 Detection difficulty
Difficulty of recognizing and confirming infection
Reference or research laboratory required: A validated assay exists, but only at a national reference or research laboratory rather than at local or regional level
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c4l3, not normally tested for at local/regional labs, but enough testing results have been published that the available methods are thought to be reliable"
Basis. ch41 41.4.4: "Swine HEV cannot be efficiently propagated in cell culture, and only a few strains of swine HEV can be grown in vitro. Currently, the diagnosis of swine HEV infection is based on PCR and/or ELISA." 41.4.3: "Pigs experimentally infected with swine HEV remained clinically normal." shic_hev: "HEV is not cultivatable in cell culture. The most common and reliable assay for HEV detection is the reverse transcriptase polymerase chain reaction (RT-PCR)." "Enzyme linked immunosorbent assays (ELISAs) have been developed for antibody detection, including one commercially available kit that detects antibodies to HEV-1 and HEV-3." "HEV is ubiquitous and difficult to detect."
How this level was decided
INFERRED. Nothing in the pig prompts a test -- infection is clinically silent -- so level 1 is out. PCR and ELISA exist and have been used at scale, including a 25-slaughterhouse survey across 10 states, which is real capability. But that is surveillance and research work rather than a service a practitioner requests, and the virus cannot be reliably cultured. Level 3 under the reworded criterion. The inference is that the assays, though well established, are not offered at local or regional level; if a diagnostic laboratory would run an HEV PCR on request, this is level 2. Level 3 held, and noting the tension: a commercially available antibody kit exists, which pulls toward 2. Held because the virus does not culture, the factsheet calls it difficult to detect, and infection in pigs is asymptomatic -- so nothing clinical prompts the request, which is the level 3 situation.
C5 Production cost
Financial impact on the infected farm's cost of production
Negligible: No measurable effect on cost of production
Basis. ch41 41.4.3: "Pigs experimentally infected with swine HEV remained clinically normal, but mild-to-moderate enlargement of hepatic and mesenteric lymph nodes was observed." Microscopic hepatitis and focal hepatocellular necrosis occur, peaking at 20 DPI. "Pregnant gilts infected with swine HEV had mild hepatitis and individual hepatocellular necrosis in some gilts, but HEV-associated lesions in the reproductive tract or fetuses were absent." shic_hev: "HEV infections in swine are usually asymptomatic. Increased liver enzymes have been reported in experimental studies." "Although morbidity can be high, especially in pigs 2-4 months of age, death is uncommon."
How this level was decided
Clinically normal pigs, microscopic lesions only, and no reproductive effect even in experimentally infected pregnant gilts. No measurable effect on cost of production. Level 1. The whole weight of this entry sits on the human side, which is where C1 and C2 carry it. Level 1 confirmed -- usually asymptomatic, no production consequence.
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, agent seems to be widespread in the US so diagnosis would not be likely to cause a market impact"
Basis. ch41 41.4.5: "HEV was ranked #6 for risk of spillover and zoonotic infection", and "a recent joint FAO/WHO expert committee ranked HEV in the top three foodborne viral pathogen along with norovirus and hepatitis A virus, and pork was identified as an important virus-commodity pair of global public health burden". No trade measure, movement control or consumer response is recorded.
How this level was decided
INFERRED, and the least comfortable level 1 in this batch. Under the standing note SCORING/market_impact, HEV is already endemic in US pigs -- 6.3% of market animals viraemic -- and has never produced a market response, which is the test the note sets. FLAGGED FOR ERIC: the FAO/WHO ranking of pork as a top-three foodborne viral commodity pair is exactly the kind of finding that precedes regulatory attention, and the note is explicitly scoped to what HAS happened rather than what may. If he reads the ranking as a live signal rather than a background assessment, this is level 2. Unchanged. Present on 80-100% of US farms with no market event.
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. ch41 41.4.3: "Pigs experimentally infected with swine HEV remained clinically normal." No antiviral for pigs is described anywhere in 41.4.
How this level was decided
No treatment exists, but the second clause of level 1 holds squarely: the pigs are not ill. There is no animal outcome for a treatment to improve. NOTE: treating pigs to reduce human exposure would be a food safety intervention rather than a pathogen-directed treatment improving the pig outcome -- the same distinction drawn on campylobacter_spp and yersinia_enterocolitica, both of which Eric confirmed at level 1. Unchanged. Asymptomatic in pigs, so nothing to treat.
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. ch41 41.4.5: "A commercial vaccine against HEV ('HEV 239') is currently licensed for human use in China. It may be advantageous to vaccinate pigs to decrease the potential for zoonotic transmission and eliminate pork safety concerns." "The major concern for swine HEV is its zoonotic risk and pork safety." shic_hev: "A highly protective recombinant vaccine, HEV 239, has been developed for use in humans but has not been tested in swine." "Little is known about... vaccine efficacy in swine."
How this level was decided
Level 3, and a genuine one under the reworded criterion. No swine vaccine exists in the US, and the chapter states the need in its own voice -- it may be advantageous to vaccinate pigs, to remove a zoonotic risk and a pork safety concern. The target is also demonstrably tractable: a licensed human HEV vaccine already exists. Needed, achievable, and not available. NOTE: this differs from the level 1 entries in this batch precisely because the benefit is real and named, even though the pig itself is not sick. Level 3 confirmed, and this is an instructive instance of the level. The imperative here is not a pig disease -- infection is asymptomatic in pigs -- but a FOOD SAFETY one, since pigs are the most important reservoir for the human-infecting genotypes. Tractability is demonstrated: a highly protective recombinant human vaccine exists and simply has never been tested in swine. That is a genuine and unusually well-defined gap.
Levels and evidence are generated from data/assignments/hepatitis_e_virus.yml; the overview is authored in data/overviews/hepatitis_e_virus.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.