Emc virus humans

Progress on xenografts, such as pig heart transplantation in humans, has raised safety concerns that need to be explored. In this review we will highlight the biology of EMCV and all known and potential virulence factors. Mice inoculated intravenously, intraperitoneally, subcutaneously, intracranially or by intranasal instillation with filtered edema fluid from the gibbon developed paralysis of the posterior members and a myocarditis followed by death in a week.

The pathogenic agent was at that time named the encephalomyocarditis virus. In , a Mengo virus was isolated by Dick et al. It was isolated from a captive rhesus monkey that had developed hind limb paralysis. In , cross sero-neutralization studies showed that Mengo, EMCV were antigenically indistinct from each other, meaning they are part of the same species.

The L and 2A, two proteins that are considered as viral security proteins or virulence factor, are the most divergent. The EMCV, like other picornaviruses, is a small non-enveloped virus, with an icosahedric capsid of 30 nm diameter 10 and a genome consisting of a positive single-stranded RNA of approximately 7.

The viral RNA is infectious in and of itself, meaning that viral proteins are not required to initiate viral gene expression, and thus its introduction by transfection into cells suffices for production of infectious viral particles. The genome has a unique coding region flanked by two untranslated regions UTR.

Figure 1. A Genomic organization. The polyproteins is cleaved by the 3C protease, cleavage sites are indicated black triangles. Ribosome skinping curved right arrow.

B Description of EMCV proteins properties and functions known or assumed by similarity with other picornaviruses. Adjacent to the poly C tract are some pseudoknots with unknown function. The IRES of picornaviruses fall into five categories, based on conserved primary and secondary structure 14 for review see ref. It is subdivided into five structural domains designated H-L, and immediately upstream of the initiation codon AUG a pyrimidine rich tract is found.

The genome of picornaviruses also contains a higher-order RNA structure, the cis-acting replication element CRE , used as a template for 3D polymerase-mediated VPg uridylation, necessary for initiation of viral RNA replication. The EMCV genome is represented in Figure 1 and the accompanying table describes EMCV proteins and summarizes, in their respective order within the polyprotein, their known functions.

In this review we highlight what has been shown for EMCV and what has been assumed from study of other picornaviruses. In the next paragraphs we used the term picornaviruses to designate that as far as we know it has not been clearly proven for EMCV but it has been shown for other picornaviruses. The Mengovirus has been crystallized and analyzed by X-ray diffraction. Five protomers assemble into a pentamer and 12 pentamers are necessary to form the capsid.

The capsid is organized around symmetric axes of 2-, 3- and 5-fold symmetry. Five VP1 proteins are grouped around the 5-fold symmetry axis, while VP2 and VP3 proteins alternate around the 3-fold symmetry axis. The extremities of the branches are constituted of prominent structures loops that are the most exposed region at the surface of the Mengo capsid.

Each branch of the star is separated by a depression called the pit. The pit corresponds to the contact region between VP1 and VP3. By analogy, it has been supposed that the Mengo pit would serve as a receptor binding site. The time scale given in the figure legend is specific for BHK and might vary upon the cell type and the EMCV strain use for the infection. Figure 2.

Encephalomyocarditis viral replication cycle. The virion binds to a cellular receptor. After uncoating, the genomic RNA is released by an unknown mechanism. The polyprotein is cleaved during and after the translation, leading to precursors or mature proteins. Some of those proteins allow formation of the membranous vesicles where genome replication will occur.

Those new positive genomic RNAs will either serve for translation after removal of VPg, serve as matrix for synthesis of new viral RNAs or will be encapsidated. Five protomers will assemble into pentamers and 12 of them will form the icosahedric capsid. Virions are then egress by cell lysis. Modified from ref. To initiate the infection, the first step is the attachment of the virus particle to a cell membrane molecule: a receptor or coreceptor. Thus, the main receptor for EMCV, as well as its viral binding partner, remains uncertain.

A recent study suggests that the capacity of the virus to interact with cell surface sialic acid residues is important for infection of BRL cells.

The mechanisms involved in internalization and uncoating of cardioviruses are poorly documented. Thus, unlike FMDV whose entry requires receptor-mediated endocytosis and endosomal acidification, it is believed for EMCV that interaction of the viral particle with a cellular receptor suffices to induce the conformational changes of the capsid shell required for viral RNA delivery into the cytoplasm.

VP1 N-terminal extremities have an amphipathic helix that inserts into the cell membrane and allows the formation of a pore through which the viral RNA is thought to be injected into the cell. Once the genomic RNA is in the cytoplasm, it must be translated as it cannot be replicated by cellular RNA polymerases and no viral enzymes are brought along with the viral particle.

This VPg does not have any known role in translation and can be detached from the viral RNA by a cellular enzyme. There exist five types of IRES that differ in their primary and secondary structures, the location of the initiation codon and their activity in different cell types. All picornaviruses possess an IRES. In both cases, the 60S ribosomal subunit joins the complex at the AUG initiation codon, initiation factors are released, and elongation ensues.

The translation of picornaviral RNA leads to synthesis of viral proteins, some of which inhibit cap-dependent translation. The cardioviruses that possess only one protease, 3C, seem to have developed different strategies that enable inhibition of host cell translation, even if this inhibition is slower and less efficient.

Figure 3. Encephalomyocarditis viral 2A protein. However, the first instance of polyprotein processing is not proteolytic, and indeed occurs during translation between the 2A and 2B protein, before EMCV 3C pro synthesis. The NPG P sequence at the junction between these two proteins leads to ribosome skipping; no peptide bond is made between the glutamine G of 2A and the proline P of 2B, resulting in production of two separate peptides for details see Fig.

It is a cysteine protease that exhibits a high degree of substrate specificity. Comparison of known cleavage sites of the EMCV viral protease has failed to reveal a clear consensus sequence, although some common determinants can be identified. EMCV 3C pro has been described to be extremely labile in vitro and in vivo.

During EMCV infection, once the 3C protease is translated, it is immediately active and starts to cleave the polyprotein in cis. When detached from the polyprotein, 3C pro can also cleave newly synthesized polyproteins in trans.

EMCV 3C pro cleavage sites within the polyprotein are indicated by small black triangles in Figure 1. Replication of the picornavirus genome occurs within the cytoplasm. Picornavirus infection leads to intracellular membranous proliferation and rearrangements. The endoplasmic reticulum ER and Golgi apparatus are rearranged and the cytoplasm fills up with bilayer membranous vesicles. The enterovirus 2B protein is a small hydrophobic protein.

The 2B protein is a viroporin, 42 able to form transmembranous pores, which could explain this calcium flux. In addition to membrane rearrangements, it inhibits protein trafficking through the Golgi complex. However, De Jong et al. In addition, the 3A protein, which is a small transmembraneous hydrophobic protein, has also been found in the membranous complex. It is assumed that the lipids that make up the membranous vesicles are derived from the ER.

Indeed, during PV infection, it has been shown that the vesicles of the replication complex resemble those of the autophagic pathway, in that they possess double membrane structures, cytoplasmic components within the vesicles, and typical autophagic markers such as LC3 and LAMP1 latency-associated membrane protein 1.

Thus, viral replication of EMCV is believed to occur in the cytosol within the replication complex localized at the surface of clustered membranous vesicles. Again, very few studies have addressed the replication of EMCV, and most of our assumptions are based on extrapolation from studies performed with enteroviruses. The model developed for poliovirus replication is believed to hold for other picornaviruses, but this awaits confirmation.

It is commonly accepted that translation of picornaviruses must stop to allow transcription of the negative strand viral RNA, 56 negative RNA synthesis being the first step of viral RNA replication. The mechanism governing the shift from translation to replication is not fully determined, although a model has recently been proposed for PV.

The initiation of negative strand RNA synthesis of picornaviruses is still controversial. Interestingly, the position of the cre within the genome seems not to be critical and can even be provided in trans. The elongation of the negative strand leads to the formation of a double-stranded RNA structure called the replication form RF.

Picornavirus positive strand synthesis initiation from the RF has not been elucidated. Two main hypotheses have been proposed for VPg-pUpU generation. The first hypothesis suggests that initiation of positive strand synthesis may use VPg proteins that have already been uridylylated, in excess, during negative strand synthesis.

The RF structure is presumed to be unwound for positive strand synthesis. The 2C viral protein possesses an ATP ase activity and a putative helicase domain even if helicase activity has never been reported , and seems to be important for positive RNA synthesis.

This interaction probably destabilizes the RF. However, cellular helicases and nuclear proteins might also be implicated, as the RF structure is infectious when used to transfect non-enucleated cells.

Indeed, there is formation of partially double-stranded RNA, corresponding to the replication intermediates RI that allows simultaneous synthesis of several positive RNA strands from a single negative RNA template. The last steps in the EMCV viral cycle are encapsidation of newly synthesized viral RNA, maturation of the provirions and virus release from the cell. The mechanisms involved in encapsidation and maturation are still unresolved and are probably the least studied steps of the viral cycle.

The formation of viral particles occurs in the cytosol through the 3C pro cleavage of the P1 precursor, releasing VP0, VP1 and VP3 that auto-assemble to form a protomer containing a single copy of each protein. Five protomers form a pentamer and 12 pentamers auto-assemble to form the icosahedric capsid. There are two models for picornavirus RNA encapsidation. A first model proposes that the protomers assemble into empty capsid and that the viral RNA is then inserted into the capsid.

This is supported by the observation that empty capsids are found during picornavirus infection, but has never been formally proven. A second model proposes that the pentamers assemble directly around the neo-synthesized viral RNA. Substitution of P1 by a reporter gene in several picornaviruses does not perturb viral RNA encapsidation when capsid proteins are provided in trans. In fact, numerous attempts to identify an RNA encapsidation signal have failed.

They showed that for chimeric viruses composed of PV and Cox that are unable to support encapsidation, the encapsidation process could be restored if the P1 and 2C proteins originate from the same virus.

Previous studies on heterologous encapsidation 68 have shown that the PV replicon could be encapsidated into coxsackie B3 virus CBV3 , human rhinovirus 14 RHV14 and mengovirus capsids.

It should be noted that the capsid proteins were provided by the expression of the full viral cDNA under control of a T7 promoter, indicating that their 2C proteins were certainly present. This cleavage is considered to be autocatalytic and would result from a local activation of water molecules by a His residue in the VP2.

This would lead to a nucleophilic attack on the scissile bond and cleavage. Indeed, it is possible that VP0 cleavage is required for the subsequent release of viral RNA into the cytoplasm of newly infected cells. EMCV is a rapidly lytic virus that causes necrotic cell death within 7 to 10 h. Several hypotheses have been advanced, such as cell burst due to accumulation of viral particules or proteins in the cell or permeabilization of cell membranes due to viroporins like the 2C of PV. EMCV was first isolated from a gibbon in in Florida, 1 and then from swine following an epizootic in Panama in A non-exhaustive list of animals from which EMCV has been isolated includes voles, squirrels, elephants, swine, wild boar, racoons, antelope, lions, birds and several species of non-human primates.

All together these studies indicate that EMCV has a worldwide distribution and can infect a wide range of animal species. Its natural reservoir is thought to be rodents mouse or rats. Indeed rat infections are usually asymptomatic and the virus can replicate and be excreted up to 29 d post-infection. EMCV is quite stable in a large spectrum of pH and resistant to ether treatment. The EMCV has often been described as a potential zoonotic agent. Nevertheless, an association between human infection and disease has still not been clearly established.

Some experimental infections on human explants or human primary cell cultures have been described and clearly point out that human cells are sensitive to EMCV. Between and childhood infections associated with fever and encephalitis but no myocarditis were described in Germany and Holland.

Unfortunately, these strains are no longer available for further characterization. These soldiers presented febrile illness for 3 d. Three patients out of the four presented an increase in neutralizing antibody titer.

Meanwhile, the virus was isolated from his blood. From to , no EMCV infections associated with clinical signs were reported. However, serological studies performed on healthy persons revealed a prevalence of 2. Two recent studies, performed in Peru, described human cases. Patients presented febrile illness, likely due to EMCV infection. Indeed, virus was isolated during the acute phase for two patients with nausea, headache and dyspnea. Upon molecular diagnosis, no virus other than EMCV was detected.

There is considerable variation in the severity and location of lesions caused by EMCV in the broad range of susceptible hosts. However, EMCV pathogenesis has mostly been studied in rodents, swine and monkeys.

General symptoms in non-human primates, such as baboons, gibbons, chimpanzees, green and rhesus monkeys, are mainly death and labored respiration associated with acute heart failure. The salient necropsy findings are pulmonary congestion and edema, hydropericardium, hydrothorax, ascites, lymph node and splenic hypertrophy, and pale white-to-tan mottled hearts.

Placental infection with fetal loss can also occur. Infection of monkeys can lead to high mortality in primatology centers, as occurred in a baboon colony in San Antonio in , and more recently in a group of rhesus macaques.

EMCV usually induces acute focal myocarditis with sudden death in pigs. Myocarditis is characterized by cardiac inflammation and cardiomyocyte necrosis. Other symptoms have been observed, such as anorexia, apathy, palsy, paralysis or dyspnea.

Experimentally infected piglets show high fever, followed by death within 2 to 11 d, but can sometimes recover with chronic myocarditis. Mortality decreases with age. After oro-nasal infection of piglets, viruses are thought to spread from tonsils to target organs by means of infected circulating monocytes.

The virus can be detected in the myocardium, even when myocardial lesions are small or absent. Histological analysis of piglet hearts reveals myocarditis associated with scattered or localized infiltration and accumulation of mononuclear cells, vascular congestion, edema and myocardial fiber degeneration, with necrosis.

In the brain, congestion is accompanied by meningitis, perivascular infiltration of mononuclear cells and neuronal degeneration. Reproductive disorders including abortion, fetal death or mummification have been described in infected females. EMCV infection can be asymptomatic, 90 but in mice generally induces encephalitis, member paralysis, 78 , - myocarditis or type 1 diabetes.

Susceptibility to EMCV infection differs according to the strain and age of mice, and the viral strain and dose of inoculum. Infection of mice with different EMCV strains results in a wide spectrum of clinical manifestations, ranging from inapparent infection to severe disease and death. EMCV-induced myocarditis is characterized by myocardial necrosis and cellular infiltration. It has been widely used as a model to study viral-induced myocarditis.

Many studies seem to indicate that the inflammatory response is deleterious, - but discordant data do exist. Hind limb paralysis and encephalitis have been documented during EMCV infection.

Upon administration of a high dose of inoculum, mice show encephalitis and paralysis within 4 d of infection and no recovery. Infection of genetically susceptible mouse strains with a high dose of EMCV D leads to diabetes within 3 to 4 d. As described in the previous section, EMCV is known to induce myocarditis, diabetes and reproductive and nervous disorders.

It is believed that symptoms and disease are viral strain-specific. Animal species, sex and age are also known to be important factors for EMCV virulence. Few molecular determinants of EMCV virulence have been defined so far. This chapter will describe them and highlight what should be considered to be potential factors in EMCV virulence.

The first primordial steps that can modulate EMCV virulence is the ability of the virus to adsorb to the cell and gain entry. The viral capsid proteins, in their capacity to interact with cellular receptors, are crucial for this entry step and may be considered to be factors that can modulate EMCV virulence. As regards diabetes induced by EMCV, the genetic background of the mouse is also an important factor. Zhu and colleagues recently observed that mutation of the threonine at position of the VP1 protein decreases the neurovirulence of EMCV.

Substitution of the Thr with an isoleucine or a proline reduced the ability of EMCV to grow in the brain of infected mice. The mutants induced only moderate inflammatory responses and less brain damage, but still caused mortality when inoculated at high doses.

Thus, the VP1 protein of EMCV influences virulent properties, because it is structure by which the virus attaches to its cell receptor and is essential for virus adsorption and entry. However, it should be noted that mutations within viral capsids may also be deleterious for viral assembly as well as release.

Indeed, delay in viral release could probably be sufficient to attenuate virulence. It has been clearly demonstrated that diminution of the length of the Mengovirus poly C strikingly attenuated its virulence, rendering it non-pathogenic in mice.

LaRue et al. The fact that a short poly C tract is less deleterious for EMCV strains than for the Mengovirus strain indicates that the viral genomic context might influence the degree to which virulence is dependent upon the length of the poly C tract. Viral strain sensitivity to the poly C tract length is suspected to be due to a defect in viral replication in certain cell types. Very recently, Loughran et al. This process could be important in regulating virus gene expression and may play some sort of regulatory role in the viral lifecycle.

A definitive diagnosis can be confirmed by virus isolation from infected heart tissue from the acute phase of the disease.

Cardiomegaly and myocardial lesions with yellow or white necrotic foci mm diameter are common and usually present on the epicardium of the right ventricle. These lesions can also be characteristic of Vitamin E and selenium deficiency. Acutely affected pigs may not show any gross lesions on post mortem. Infected foetuses can grossly vary depending on the stage of pregnancy and infection and myocardial lesions may be indistinguishable from other viral infections.

Foetuses can be haemorrhagic, oedematous or apparently normal. Histopathological findings include myocarditis with focal or diffuse accumulation of mononuclear cells, vascular congestion, oedema, degeneration of the myocardial fibres with necrosis and occasional mineralization of necrotic heart muscle. Brain tissue can be congested with evidence of meningitis, perivascular infiltration mononuclear cells and neuronal degeneration. Nonsuppurative encephalitis and myocarditis has also been seen in naturally infected swine foetuses.

Detection of antibody specific to EMCV from still-born piglets has been used to confirm foetal infection [3] [4]. There is no specific treatment. Mortality levels in at risk pigs can be reduced by avoiding stress or excitation. It is important to control rodent populations on farm to prevent the spread of disease and contamination of feeds or water supply. Good husbandry and hygiene protocols should be followed with the regular use of disinfectants.

This article has been expert reviewed by Dr Mandy Nevel. From WikiVet English. The novel coronavirus which was discovered this summer in the Middle East might infect more than just human patients. The pathogen is closely related to SARS, and it may also be able to infect pigs and a wide range of bat species.

The scientists published their findings in the journal mBio. The findings might help public health officials track the source of the outbreak and identify the role of wild animals and livestock in the spread of the virus. Cases have appeared in Qatar and Jordan, and researchers have confirmed nine infections, including five deaths.

The virus has been fully sequenced and its genome revealed that it is closely related to the SARS coronavirus.