Encephalomyocarditis virus (EMCV) is a globally distributed pathogen recognized for causing disease across various animal species. This viral infection primarily impacts mammals, leading to a range of clinical presentations. Understanding EMCV’s characteristics and spread is important for animal health management and disease prevention efforts worldwide.
Understanding Encephalomyocarditis Virus
Encephalomyocarditis virus is a single-stranded RNA virus that belongs to the Picornaviridae family and the Cardiovirus genus. This non-enveloped virus lacks an outer lipid membrane, contributing to its stability. While EMCV has a broad host range, domestic swine are particularly susceptible, causing considerable economic losses.
Beyond swine, EMCV can infect a wide array of other mammalian species. Rodents, particularly rats and mice, are primary natural reservoirs, often carrying the infection without symptoms. Other susceptible animals include elephants, non-human primates, wild boars, raccoons, lions, and various ungulates. The virus is found globally, with outbreaks reported across continents, and is of economic importance in tropical areas.
How EMCV Spreads
The main route for EMCV transmission is through ingestion of contaminated feed or water. Rodents play a significant role, shedding the virus in their feces and urine, which can contaminate animal feed and water sources. Rats can shed the virus for up to a month after infection, contributing to environmental contamination.
Infected rodent carcasses can also serve as a source of infection when ingested by other animals. While direct animal-to-animal transmission, particularly between pigs, is not widely observed as a primary route, infected pigs can shed the virus in nasal secretions and feces for a short period (first 3 days). The virus is resistant to environmental conditions and can remain infectious for weeks to several months.
Recognizing EMCV Infection
Clinical signs of EMCV infection vary by host species and age, with swine showing distinct manifestations. In young piglets, infection often leads to sudden death, usually attributed to acute heart failure or myocarditis. Mortality rates in pre-weaning piglets can be as high as 100%. Affected piglets may also display signs such as lethargy, fever, anorexia, labored breathing, trembling, staggering, paralysis, or vomiting.
Infected pregnant sows can experience reproductive failure, including mummified fetuses, stillbirths, and abortions, often occurring in late gestation. Older pigs typically have subclinical infections, showing no overt signs of illness, though some may develop chronic myocarditis.
Diagnosis is often initially based on clinical signs and herd history. Definitive confirmation involves laboratory tests such as virus isolation from affected tissues (e.g., myocardium or spleen), reverse transcriptase polymerase chain reaction (RT-PCR), or serological tests like virus neutralization and enzyme-linked immunosorbent assay (ELISA). Histopathological examination of tissues can reveal characteristic lesions in the heart and brain.
Controlling and Preventing EMCV
Controlling and preventing EMCV outbreaks depends on implementing strict biosecurity measures within animal husbandry settings. This includes managing farm access to prevent virus introduction and maintaining rigorous hygiene for facilities and equipment. Covering feed to prevent contamination by rodent excreta is important.
Rodent control programs are a primary strategy for limiting EMCV spread, as wild rats and mice are significant reservoirs and disseminators. Effective measures include baiting and trapping to reduce rodent populations. When infection occurs, isolation of affected animals and proper disposal of infected carcasses are recommended to prevent further environmental contamination. While inactivated vaccines are available for some domestic and wild animals, including experimental options for pigs, non-human primates, and ungulates, their broad commercial availability and efficacy can be limited. Research continues into developing more widely applicable and effective vaccines.
EMCV and Human Health
Encephalomyocarditis virus is recognized as having zoonotic potential, meaning it can transmit from animals to humans. Documented human infections are uncommon, and when they do occur, they are frequently asymptomatic or result in mild illness. Individuals who experience symptoms report flu-like signs such as fever, chills, nausea, headaches, and vomiting.
In rare instances, more pronounced neurological symptoms like nuchal rigidity or delirium have been reported. Human infections are associated with significant exposure to infected animals or their environments, commonly seen in occupations like swine farm workers, zookeepers, and veterinarians. Despite its ability to infect humans, EMCV is not widely regarded as a major public health concern. There is no documented evidence of direct pig-to-human transmission, though the potential for transmission from pigs used in xenografts is a consideration.