Encephalomyocarditis Virus
LEVELS: Highly unlikely; Mild; Routine biosecurity keeps it out; Laboratory-dependent; Moderate; Negligible; Substantial; Available but inconsistent
| Register id | encephalomyocarditis_virus |
| Type | virus |
| Scientific name | Encephalomyocarditis virus |
| NCBI taxid | 12104 |
| Evidence | 2 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
Encephalomyocarditis virus is essentially a rodent virus that spills over into pigs. It has been isolated from more than thirty mammal and bird species, but the strains found in pigs, wild boar and rats are genetically almost identical, which points to rats as the link; contaminated feed and water, and rodent carcasses eaten by pigs, are the recognised sources, and the presence of mice is the strongest risk factor for an outbreak. Infection of pigs is not uncommon but disease is infrequent, and outbreaks tend to cluster in particular endemic areas. When disease does occur it takes two forms. In preweaning piglets the virus attacks the heart, and mortality can approach 100% — the pigs are usually simply found dead, often in the late afternoon when they have been most active, with deaths confined to one barn. In breeding females it causes reproductive failure, with abortion, mummified and stillborn fetuses. Pigs from weaning to adulthood are usually infected without signs. There is no specific treatment, though avoiding stress and excitement during an outbreak reduces deaths. An inactivated vaccine was formerly available in the United States and gave good protection; there is little antigenic variation, so cross-protection is broad. Its public health impact is regarded as minimal.
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, the zimmerman data is more reliable and we will let it guide teh L decision" -- ruling on the flag the pass raised, which set out both sides and could not choose between them. The Zimmerman study found no association between EMCV infection and disease in the people most exposed to it, veterinarians, animal caretakers and laboratory staff; against it stood 47% seropositivity in Mexican swine-specialist veterinarians and two Peruvian febrile cases whose viruses were "most closely related to EMC viruses isolated from pigs in Europe". He rules that the negative occupational study outweighs the seroprevalence and the phylogenetic proximity, which is the reworded level 1 -- human infection reported but not attributed to pig or pork exposure.
Basis. ch36 36.4.3: "The impact of EMCV on public health is believed to be minimal. Despite the frequency of infection in swine, Zimmerman (1994) found no association between infection and transmission of disease to persons at risk (veterinarians, animal caretakers, and laboratory staff). Surveillance of pig pathogens in Sarawak, Malaysia did not detect EMCV in nasal samples of humans working at the human-pig interface." "In Mexico (2011), 47% of blood samples from swine-specialist veterinarians (n = 85) sampled during a congress were seropositive." "In 2009, EMCV was isolated in unrelated cases from two people with febrile illness in Peru. These viruses were most closely related to EMC viruses isolated from pigs in Europe." shic_emcv: "Infections in humans appear to be mainly asymptomatic. Pig-to-human transmission has not been documented but remains a concern where pigs are used as donors for human xenografts."
How this level was decided
MOVED L2 -> L1, re-read 2026-09-04 AGAINST THE REWORDED LABELS. FLAG. No association was found in occupationally exposed people and no detection at the human-pig interface in Malaysia. Against that, 47% seropositivity in swine-specialist veterinarians and two Peruvian febrile cases whose viruses were "most closely related to EMC viruses isolated from pigs in Europe" -- which is phylogenetic proximity, not attribution. EMCV is fundamentally a rodent virus and people may be acquiring it from the same rodents the pigs do.
PREVIOUS ANSWER, kept because the evidence behind it has not changed, only the level boundary: The folder pulls both ways and level 2 is where it lands. Against a pig route: no association found in occupationally exposed people, and no detection at the human-pig interface in Malaysia. For it: 47% seropositivity in swine-specialist veterinarians, and two human febrile cases whose viruses were most closely related to pig isolates. That is transmission that is plausible and occasionally reported, with nothing in pig production directed at preventing it. Both clauses of level 2. NOTE: EMCV is fundamentally a rodent virus and people may be acquiring it from the same rodents the pigs do, which would make the pig a co-victim rather than a source -- the dead-end pattern Eric ruled on for chikungunya. The veterinarian seroprevalence is the reason it is not scored level 1. Level 1 confirmed on the second clause: human infection occurs and is not attributed to pigs. The xenograft caveat is a hypothetical route through a procedure, not a reported transmission.
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, a few human cases have been identified but without enough evidence to move this to L3 and is also a risk related to xenotransplant so should not be L1"
Basis. ch36 36.4.3: "In 2009, EMCV was isolated in unrelated cases from two people with febrile illness in Peru." "secondary infections in immunocompromised persons can be expected to occur." "a myocardial strain (B279/95) and a rat strain (1086C) of EMCV productively infected primary human cardiomyocytes and induced complete cytolysis." "The impact of EMCV on public health is believed to be minimal." shic_emcv: "Infections in humans appear to be mainly asymptomatic."
How this level was decided
INFERRED. The only human clinical description in the folder is febrile illness in two people, and the chapter judges the public health impact minimal. Usually mild and self-limiting with serious disease rare is level 2. NOTE FOR ERIC: the chapter also records that EMCV lyses human cardiomyocytes in culture and flags the risk if pigs are used as xenotransplant donors, which is a mechanism for severe disease rather than a report of one. Scoring the demonstrated illness rather than the demonstrated mechanism keeps this at level 2, and the general rule forbids scoring hypothetical futures. Level 2 held. Mainly asymptomatic pulls toward 1, but the agent is named for the encephalitis and myocarditis it can cause, and level 2 is the mild-and-self-limiting level rather than a claim of no illness.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Routine biosecurity keeps it out: Quarantine of incoming stock, transport and fomite control, cleaning and disinfection, and the usual monitoring reliably exclude it
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED at level 3 on the C3 review sheet. "l3, probably is in a lot of pig populations subclinically but we also know is carried in rodents so in theory, if you start with a clean herd, l3 should keep it out. Reality is, may actually take l4 to keep it out but evidence is unclear so we leave at l3" NOTE HOW HE DECIDED IT, because it is the opposite of a default: he says the true answer may be level 4, and holds level 3 because the evidence for level 4 is unclear. The level is the one the evidence supports, not the one the worry suggests.
Basis. ch36 36.4.4: "EMCV is generally regarded as a rodent virus, although EMC viruses have been isolated from over 30 species of mammals and birds." "Complete genome sequences and phylogenetic analysis indicated that EMCV strains isolated from pigs, wild boar, and rats had high homology with each other, which implies that rats may play an important role in EMCV transmission between domestic pigs and wild boar." "Feed and water contaminated with EMCV by rodents or contaminated rodent carcasses are considered important sources of swine infection." "the presence of mice was the most significant risk factor for clinical EMCV infection." 36.4.10: "pig producers, especially in endemic areas, are advised to maintain rodent control to prevent clinical outbreaks." shic_emcv: "Rodents are thought to be the reservoir species." "Ingestion, either of EMCV-infected carcasses (rats or mice) or of food/water contaminated by infected carcasses, is thought to be the primary route of transmission in swine. Direct pig-to-pig transmission has not been demonstrated." "Prevention of EMCV infection is based on rodent control... Rodents can be excluded from buildings by sealing cracks and areas around water pipes and electrical wires. Baiting and trapping can also reduce rodent populations."
How this level was decided
MOVED L5 -> L3 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. rats. Rodents get into barns and housing does not stop them; what keeps EMCV out is a rodent control programme run continuously, which is the level 3 list.
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. A rodent reservoir, established wherever pigs are kept, feeding into the herd through contaminated feed, water and carcasses. That is a reservoir outside the pig industry giving continuous opportunity for exposure, and the chapter reinforces it by reporting that a single introduction is unlikely to sustain an outbreak by pig-to-pig spread alone -- repeated introduction from the rodent reservoir is what drives it. Level 4. Rodent control suppresses exposure but does not remove the reservoir. Level 3 confirmed, and the factsheet lays out the whole argument: the route is rodents and rodent carcasses in feed and water, pig-to-pig spread has never been demonstrated, and the control is a rodent programme -- sealing, baiting, trapping, feed hygiene. That is the routine biosecurity list, and a building alone does not deliver 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, differences of opinion amongst vets and diagnosticians as to the significance of this infection but easy to test for by request"
Basis. ch36 36.4.8: "In most cases, the piglets are found dead without any clinical signs. In finishing pigs, sudden death is also the most characteristic sign... The disease is often restricted to one barn and deaths often occur in the late afternoon when the pigs are most active." "A variable degree of nonsuppurative interstitial myocarditis or encephalitis is indicative of EMCV infection. A conclusive diagnosis of EMCV should be demonstrated by virus isolation in cell culture and confirmation by real-time RT-PCR." "The VN and ELISA are the most commonly used methods and have been shown to be diagnostically specific." shic_emcv: "Reverse transcriptase polymerase chain reaction (RT-PCR) is the most common method of detection; a recently developed reverse transcriptase loop-mediated isothermal amplification method (RT-LAMP) shows promise for use in the field." "A variety of serological tests are available including virus neutralization and enzyme-linked immunosorbent assay (ELISA)."
How this level was decided
Sudden death has a long differential and the chapter lists five other agents for the reproductive presentation alone, so the clinical picture does not point here -- level 1 is out. But the histopathological lesion is described as indicative, and confirmation is cell culture with RT-PCR plus specific serology, all standard veterinary diagnostic laboratory work. Level 2. Level 2 confirmed.
C5 Production cost
Financial impact on the infected farm's cost of production
Moderate: Losses measurably increase cost of production but remain manageable within normal farm operations, whether acute, chronic, or associated with endemic disease
Basis. ch36 36.4.6: "Mortality approaching 100% can occur in pigs of preweaning age. Infections in pigs from postweaning age to adulthood are usually subclinical." "In breeding females, clinical signs may vary from inapparent infection to various forms of reproductive failure, including abortion and increased numbers of mummified and stillborn fetuses." 36.4.1: "Infection of swine with EMCV is not uncommon, but clinical disease is infrequent." "EMCV outbreaks are often clustered in so-called endemic areas." shic_emcv: "In neonatal pigs, mortality rates can reach 100%." "Sudden death can occur in neonates." "In older animals, infection is usually asymptomatic... Abortion is common in gestating sows." "Clinical cases have been reported in domestic swine in ... the United States (Hawaii, Illinois, and Iowa)."
How this level was decided
Level 3. The chapter separates infection from disease -- infection is common, clinical disease infrequent -- so this is not a standing cost on every farm. But where it does break, preweaning mortality approaching 100% plus reproductive failure in the sow herd is a measurable increase in cost of production, and the outbreaks cluster in endemic areas so affected farms see it repeatedly. Manageable within normal operations, since rodent control addresses it, which keeps it below level 4. Level 3 confirmed. Neonatal mortality to 100% and common abortion in gestating sows, against asymptomatic infection in older pigs -- measurable and manageable, with US cases on record.
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 agent well known and has no or negligible clinical affect on pigs, not expected to have any effect on markets"
Basis. Section 36.4 records no trade measure, movement control, export restriction or consumer response. EMCV is present in the United States and worldwide, and 28% of clinically normal UK slaughterhouse pigs carried antibody in one survey. shic_emcv: "Clinical cases have been reported in domestic swine in Europe, Canada, South America, Australia, Korea, China, and the United States (Hawaii, Illinois, and Iowa)."
How this level was decided
INFERRED. Under the standing note SCORING/market_impact this is an agent already present and already diagnosed in US pigs, with no historical evidence of a market move following a diagnosis. Level 1. Losses fall on the affected farm and are scored at C5. Level 1 confirmed -- diagnosed in US pigs with no market response on record, which is the endemic-and-observed case the standing note puts at level 1.
C7 Treatment potential
Potential for treatment to improve outcomes
Substantial: No effective treatment (antimicrobial, antiviral, antiparasitic, herbal or other) is available, but outcomes would meaningfully improve if one existed
Basis. ch36 36.4.10: "There is no treatment for the disease but, in the acute phase, mortality may be minimized by avoiding stress or excitement in the pigs at risk." "No specific therapeutic drugs are available but supportive treatment using acetylsalicylic acid was reported to be successful in an Italian outbreak." shic_emcv: neonatal mortality to 100%, sudden death in neonates, usually asymptomatic in older animals; no treatment is described.
How this level was decided
Level 3, and one of the few in this batch. The chapter says there is no treatment, and what it offers instead is not pathogen-directed -- reducing stress is husbandry, and acetylsalicylic acid is anti-inflammatory, which C7 explicitly excludes as adjunctive rather than pathogen-directed. Against that sits real, preventable loss: preweaning mortality approaching 100% in outbreaks. Outcomes would meaningfully improve if an effective antiviral existed. Both halves of level 3. Level 3 confirmed, and squarely on the standing note's neonate rule -- lethal in neonates and trivial in adults, so score the neonate.
C8 Vaccine availability
Availability of effective vaccines or bacterins
Available but inconsistent: Commercial or autogenous vaccines exist in the US but protection may be inconsistent
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c8l2, agree with assessment"
Basis. ch36 36.4.10: "In the past, an inactivated EMCV-1 vaccine was commercially available in the United States. The vaccine produced a strong humoral immune response in vaccinated pigs and vaccinates were protected from clinical disease when challenged with virulent EMCV that killed 60% of unvaccinated controls. Further, protection against transplacental infection was demonstrated under experimental conditions. An EMCV vaccine candidate composed of noninfectious virus-like particles has been described." 36.4.9: "Within EMCV-1 there is little antigenic variation; therefore cross-protection between all EMCV strains is likely to occur." shic_emcv: "An inactivated vaccine for EMCV is available. Virus-like particle (VLP) vaccines are also being investigated for use in swine."
How this level was decided
Level 2, and the tense in the chapter is what decides it: the inactivated vaccine WAS commercially available in the United States. It worked -- protection against a challenge that killed 60% of controls, and against transplacental infection -- and the single serotype means cross-protection is likely, so this is a tractable target rather than a hard one. But it is not on the market now, and the VLP candidates are experimental. A product that exists and works but is not currently obtainable is closer to "available but inconsistent" than to either endpoint. FLAGGED for Eric: if he reads a withdrawn product as no product, this is level 3, since EMCV is one of the few entries in this batch where a vaccine would clearly be used. Level 2 confirmed by a direct statement -- a product exists. It is the first situation level 2 covers, available but of unquantified consistency, with VLP candidates still in development behind it.
Levels and evidence are generated from data/assignments/encephalomyocarditis_virus.yml; the overview is authored in data/overviews/encephalomyocarditis_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.