ENCEPHALOMYOCARDITIS VIRUS (EMCV)
LEVELS: Rarely occurs: Requires significant failure at one or more control points for transmission to humans; Highly unlikely: No evidence of non-foodborne zoonotic transmission; Moderately effective: Requires high level of compliance with extraordinary on-farm biosecurity measures to prevent farm-to-farm transmission; Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s); Substantial: Unsustainable acute or chronic losses related to severe clinical signs in a high prevalence of animals; Negligible: Little or no market disruption when disease occurs on one or more farms; Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments; Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy; No availability: Effective treatments not currently available in the US (or have not been developed); No availability: Effective vaccines not currently available in the US (or have not been developed); Not feasible: Eradication extremely unlikely
OVERVIEW
Encephalomyocarditis virus (EMCV) is a cardiovirus first described in 1940 that causes rodent-borne disease in pigs and many other species worldwide. While infection of swine with EMCV is common, clinical disease is less frequent. When disease occurs, it takes two main forms: acute myocarditis causing sudden death primarily in young pigs (especially in the first weeks of life, with mortality approaching 100% in preweaning piglets), and reproductive failure in sows. EMCV is distributed globally with outbreaks reported in Australia, South Africa, New Zealand, Cuba, Canada, and throughout Europe. Clinical disease often clusters in "endemic areas"—in Belgium, Italy, Greece, and Cyprus, outbreaks of acute myocarditis have been repeatedly documented. Rodents, particularly rats, serve as the primary reservoir, shedding virus in feces and urine for extended periods (up to 62 days post-infection) while remaining asymptomatic. Infected rodent carcasses in feed and water are considered important sources of swine infection. The presence of mice was identified as the most significant risk factor for clinical EMCV infection in epidemiological studies. EMCV also infects a remarkably wide range of species including primates, elephants, lions, and various wild mammals—zoo outbreaks have been documented following feeding of contaminated carcasses. While human infections appear rare, seroprevalence studies have found antibodies in 17-47% of humans in some endemic areas, and EMCV was isolated from two people with febrile illness in Peru (2009). An inactivated vaccine was previously commercially available in the United States but is no longer produced.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Rarely occurs: Requires significant failure at one or more control points for transmission to humans
The chapter states that "the impact of EMCV on public health is believed to be minimal" and that surveillance "did not detect EMCV in nasal samples of humans working at the human-pig interface." However, the virus has documented potential to infect humans: seroprevalence >17% was found in tropical rainforest cities in Peru; 47% of swine-specialist veterinarians in Mexico tested seropositive; and EMCV was isolated from two people with febrile illness in Peru in 2009 (viruses most closely related to European pig isolates). While direct foodborne transmission has not been documented, the evidence of human infection and the presence of virus in pig tissues suggests theoretical risk. The chapter notes that "secondary infections in immunocompromised persons can be expected to occur" and that EMCV may become more important "if pigs are used as donors for human xenografts"—experimental infection of mice through transplantation of EMCV-infected pig organs validates this concern.
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No evidence of non-foodborne zoonotic transmission
Human infection with EMCV occurs but appears rare despite widespread viral circulation in animal populations. The chapter cites seroprevalence studies showing 17-47% seropositivity in humans in endemic areas (Peru, Mexico), suggesting occupational or environmental exposure occurs. Two human cases of febrile illness with virus isolation were documented in Peru (2009). Experimental studies show EMCV "productively infected primary human cardiomyocytes and induced complete cytolysis," demonstrating human cell susceptibility. However, "despite the frequency of infection in swine," no association between infection and transmission of disease to persons at occupational risk (veterinarians, animal caretakers, laboratory staff) has been established. The disease appears to be self-limiting in immunocompetent humans, but risk may be elevated in immunocompromised individuals.
EFFECTIVENESS OF ON-FARM BIOSECURITY IN PREVENTING FARM-TO-FARM TRANSMISSION
Level: Moderately effective: Requires high level of compliance with extraordinary on-farm biosecurity measures to prevent farm-to-farm transmission
EMCV transmission to pigs occurs primarily through contaminated feed and water—rodents shed virus in feces and urine, and infected rodent carcasses serve as direct sources of infection. Epidemiological studies identified clusters of risk factors: rodent presence, general farm setup, and general hygiene, with "the presence of mice was the most significant risk factor for clinical EMCV infection." Once EMCV enters a pig population, direct pig-to-pig transmission can occur "at least for a short period," and transplacental transmission is documented. However, simulation modeling suggested that "one single EMCV introduction was unlikely to cause a major outbreak by direct pig-to-pig transmission alone," and "other mechanisms, such as multiple introductions from a rodent reservoir, may be required for large outbreaks to occur." Standard biosecurity focused on rodent exclusion and control is effective—infected rodents persistently shed virus but transmission is preventable by eliminating rodent access to feed, water, and pig housing. The seasonal pattern of outbreaks (peaks in autumn) may relate to rodent behavior seeking shelter in farm buildings.
DIFFICULTY OF DETECTING AND CONFIRMING INFECTION
Level: Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s)
Clinical presentation is suggestive: sudden death in young piglets (especially 3 days to 5 weeks of age) with characteristic gross lesions (enlarged, soft, pale heart with white foci, hydropericardium, hydrothorax, pulmonary edema); reproductive failure in sows of all parities (distinguishing from parvovirus which mainly affects gilts). Histopathology showing nonsuppurative myocarditis with variable degree of lymphocyte/histiocyte/plasma cell infiltration is indicative. However, definitive diagnosis requires: virus isolation in BHK-21, HeLa, or Vero cells (rapid, complete CPE); identification by cross-neutralization with reference antiserum or fluorescent antibody staining; real-time RT-PCR for sensitive, specific detection; or lateral flow biosensor with recombinase polymerase amplification for field testing. Serology (VN, ELISA) detects antibodies with titers ≥1:16 considered significant. Differential diagnosis includes FMD (also causes myocarditis in piglets), PRRS, pseudorabies, PCV, and leptospirosis for reproductive problems.
FINANCIAL IMPACT ON FARM'S COST OF PRODUCTION
Level: Substantial: Unsustainable acute or chronic losses related to severe clinical signs in a high prevalence of animals
EMCV causes two distinct patterns of economic loss: (1) Acute mortality in young pigs: "Mortality approaching 100% can occur in pigs of preweaning age." Piglets are typically found dead without premonitory signs. In finishing pigs, sudden death affects mainly 60-70 kg animals, often occurring in late afternoon when pigs are most active. Deaths are often restricted to one barn within a farm. (2) Reproductive failure: affected sows show increased numbers of mummified and stillborn fetuses, abortion, and early farrowing. Clinical signs vary from inapparent to severe reproductive losses. In endemic areas, EMCV causes ongoing, recurring losses—Italian studies found increasing early pig deaths and seropositive farms over time. However, many infections are subclinical (seroprevalence 5-15%, occasionally >60% in endemic areas, with similar rates in farms with and without clinical disease), and adult pig mortality is uncommon. Losses are concentrated in specific endemic regions rather than uniformly distributed, making overall industry impact variable. The sporadic, clustered nature of clinical outbreaks means affected farms can experience severe losses while most operations remain unaffected.
EFFECT ON DOMESTIC OR EXPORT MARKETS
Level: Negligible: Little or no market disruption when disease occurs on one or more farms
EMCV is not a WOAH-listed disease and does not trigger trade restrictions or regulatory notifications. The virus is endemic in rodent populations worldwide, so its presence in pig populations is not unexpected and does not affect market access. Economic impacts are limited to direct production losses on affected farms rather than broader market or trade consequences. Consumer concerns are minimal given the very limited evidence of human disease despite widespread viral circulation.
PATHOGEN'S ABILITY TO DEVELOP AND SPREAD RESISTANCE
Level: Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments
EMCV is a viral pathogen (positive-sense single-stranded RNA cardiovirus) that does not carry, acquire, or transmit antimicrobial resistance genes. The virus poses no AMR concerns. EMCV is antigenically stable with essentially one serotype (EMCV-1, though a second serotype EMCV-2 was isolated from a wood mouse in Germany). Genetic variability exists in the VP1 coding region with some strains causing myocarditis, others causing reproductive failure, and some causing both, but this represents viral diversity rather than antimicrobial resistance.
AMR DEVELOPMENT DRIVEN BY DISEASE MANAGEMENT
Level: Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy
No antiviral treatments exist for EMCV. Management focuses on prevention through rodent control and environmental management. In acute outbreaks, mortality may be minimized by avoiding stress or excitement in at-risk pigs. One Italian outbreak report mentioned supportive treatment with acetylsalicylic acid. Antimicrobials are not routinely used for EMCV prevention or treatment. Any antimicrobial use would be rare, individual animal treatment for secondary complications.
AVAILABILITY OF EFFECTIVE TREATMENT OPTIONS
Level: No availability: Effective treatments not currently available in the US (or have not been developed)
No specific treatments exist for EMCV infection. Young pigs typically die suddenly before treatment could be attempted. Supportive care through stress avoidance may reduce mortality in at-risk groups during outbreaks. For reproductive failure, no treatment can reverse fetal infection. One case report mentioned acetylsalicylic acid as supportive treatment, but no antiviral drugs are available. Management focuses entirely on prevention through rodent control.
AVAILABILITY OF EFFECTIVE VACCINES OR BACTERINS
Level: No availability: Effective vaccines not currently available in the US (or have not been developed)
The chapter states: "In the past, an inactivated EMCV-1 vaccine was commercially available in the United States." This vaccine "produced a strong humoral immune response in vaccinated pigs," protected vaccinates from lethal challenge (60% mortality in controls vs. survival in vaccinates), and demonstrated protection against transplacental infection. However, this vaccine is no longer commercially available. Experimental vaccine candidates include virus-like particles (VLPs) that showed protective efficacy in mice. Currently, no commercial EMCV vaccine is available for swine anywhere in the world. Given that EMCV exists as essentially one serotype with little antigenic variation, "cross-protection between all EMCV strains is likely to occur," suggesting that an effective vaccine could provide broad protection if developed.
FEASIBILITY OF ERADICATING THE DISEASE FROM THE US
Level: Not feasible: Eradication extremely unlikely
EMCV eradication from the US pig population is not feasible because: (1) Rodent reservoir: the virus is maintained in rat and mouse populations that cannot be eradicated; infected rodents shed virus for up to 62 days while remaining asymptomatic; (2) Wildlife hosts: EMCV infects over 30 species of mammals and birds, creating multiple reservoirs beyond pigs; (3) Global distribution: the virus is present in rodent populations worldwide; (4) Continuous reintroduction risk: even if eliminated from all pig farms, reintroduction from rodent populations would be inevitable. The practical approach is farm-level prevention through rodent control. The chapter notes that farms exposed to manure through slatted floors (potentially causing low-level exposure and subclinical immunity) showed significant protection against clinical EMCV, suggesting that endemic exposure may provide some population-level protection. Control focuses on reducing clinical impact through rodent management rather than attempting eradication.