Transmission and pathogenicity of encephalomyocarditis virus (EMCV) among rats

Narrative Review of the Safety of Using Pigs for Xenotransplantation: Characteristics and Diagnostic Methods of Vertical Transmissible Viruses

Amid the deepening imbalance in the supply and demand of allogeneic organs, xenotransplantation can be a practical alternative because it makes an unlimited supply of organs possible. However, to perform xenotransplantation on patients, the source animals to be used must be free from infectious agents. This requires the breeding of animals using assisted reproductive techniques, such as somatic cell nuclear transfer, embryo transfer, and cesarean section, without colostrum derived in designated pathogen-free (DPF) facilities. Most infectious agents can be removed from animals produced via these methods, but several viruses known to pass through the placenta are not easy to remove, even with these methods. Therefore, in this narrative review, we examine the characteristics of several viruses that are important to consider in xenotransplantation due to their ability to cross the placenta, and investigate how these viruses can be detected. This review is intended to help maintain DPF facilities by preventing animals infected with the virus from entering DPF facilities and to help select pigs suitable for xenotransplantation.

Management of encephalomyocarditis virus infection in Italian pig farms: a case report

BACKGROUND

Encephalomyocarditis virus (EMCV) has been isolated from many animals, frequently as the cause of fatal myocarditis, but pigs are the most susceptible domestic specie. The virus was isolated in swine farms since 1958 in Panama and Europe from cases of sudden death in young pigs, and the main origin of outbreaks has been assumed to be local rodent populations. There is no treatment for the disease.

CASE PRESENTATION

The clinical case describes an outbreak of encephalomyocarditis virus in a farrowing (farm A) and a weaning (farm B) site, with mortality that reached 24.2% in suckling piglets and 7.7% in weaners. The farms were located in an endemic Italian area, and the outbreak was characterised by high mortality with sudden death and clinical signs due to heart failure (trembling, dispnea and fever). The rodents control program was the key action in managing the outbreak. However, in the weaning site, the lack of rodent program in some unexplored areas of the barn (false ceiling) was responsible of a longer time of resolution of the outbreak. An unusual support treatment approach from human medicine suggestion was also applied using acetylsalicylic acid for its antiphlogistic and antithrombotic effects.

CONCLUSIONS

To control the rodent population in a pig farm is often difficult and requires a deep knowledge also of the rodents habits. Considering the lack of treatment for the disease and the absence of available vaccines in several Countries, acetylsalicylic acid might be of interest for further studies as an important support for pigs' recovery.

Monitoring Urban Zoonotic Virus Activity: Are City Rats a Promising Surveillance Tool for Emerging Viruses?

Urban environments represent unique ecosystems where dense human populations may come into contact with wildlife species, some of which are established or potential reservoirs for zoonotic pathogens that cause human diseases. Finding practical ways to monitor the presence and/or abundance of zoonotic pathogens is important to estimate the risk of spillover to humans in cities. As brown rats (Rattus norvegicus) are ubiquitous in urban habitats, and are hosts of several zoonotic viruses, we conducted longitudinal sampling of brown rats in Vienna, Austria, a large population center in Central Europe. We investigated rat tissues for the presence of several zoonotic viruses, including flaviviruses, hantaviruses, coronaviruses, poxviruses, hepatitis E virus, encephalomyocarditis virus, and influenza A virus. Although we found no evidence of active infections (all were negative for viral nucleic acids) among 96 rats captured between 2016 and 2018, our study supports the findings of others, suggesting that monitoring urban rats may be an efficient way to estimate the activity of zoonotic viruses in urban environments.

Molecular characterization of encephalomyocarditis virus strains isolated from an African elephant and rats in a French zoo

In November 2013, a fatal encephalomyocarditis virus (EMCV) case in a captive African elephant (Loxodonta africana) occurred at the Réserve Africaine de Sigean, a zoo in the south of France. Here we report the molecular characterization of the EMCV strains isolated from samples collected from the dead elephant and from 3 rats (Rattus rattus) captured in the zoo at the same time. The EMCV infection was confirmed by reverse-transcription real-time PCR (RT-rtPCR) and genome sequencing. Complete genome sequencing and sequence alignment indicated that the elephant's EMCV strain was 98.1-99.9% identical to the rat EMCV isolates at the nucleotide sequence level. Phylogenetic analysis of the ORF, P1, VP1, and 3D sequences revealed that the elephant and rat strains clustered into lineage A of the EMCV 1 group. To our knowledge, molecular characterization of EMCV in France and Europe has not been reported previously in a captive elephant. The full genome analyses of EMCV isolated from an elephant and rats in the same outbreak emphasizes the role of rodents in EMCV introduction and circulation in zoos.

Mastomys natalensis is a possible natural rodent reservoir for encephalomyocarditis virus

Encephalomyocarditis virus (EMCV) infects a wide range of hosts and can cause encephalitis, myocarditis, reproductive disorders and diabetes mellitus in selected mammalian species. As for humans, EMCV infection seems to occur by the contact with animals and can cause febrile illnesses in some infected patients. Here we isolated EMCV strain ZM12/14 from a natal multimammate mouse (Mastomys natalensis: M. natalensis) in Zambia. Pairwise sequence similarity of the ZM12/14 P1 region consisting of antigenic capsid proteins showed the highest similarity of nucleotide (80.7 %) and amino acid (96.2%) sequence with EMCV serotype 1 (EMCV-1). Phylogenetic analysis revealed that ZM12/14 clustered into EMCV-1 at the P1 and P3 regions but segregated from known EMCV strains at the P2 region, suggesting a unique evolutionary history. Reverse transcription PCR (RT-PCR) screening and neutralizing antibody assays for EMCV were performed using collected tissues and serum from various rodents (n=179) captured in different areas in Zambia. We detected the EMCV genome in 19 M. natalensis (19/179=10.6 %) and neutralizing antibody for EMCV in 33 M. natalensis (33/179=18.4 %). However, we did not detect either the genome or neutralizing antibody in other rodent species. High neutralizing antibody litres (≧320) were observed in both RT-PCR-negative and -positive animals. Inoculation of ZM12/14 caused asymptomatic persistent infection in BALB/c mice with high antibody titres and high viral loads in some organs, consistent with the above epidemiological results. This study is the first report of the isolation of EMCV in Zambia, suggesting that M. natalensis may play a role as a natural reservoir of infection.

Encephalomyocarditis virus infection in alpacas

Encephalomyocarditis virus (EMCV) infection was detected by real-time reverse transcription PCR (qRT-PCR) in four adult alpacas (Vicugna pacos) from two properties on the Far North Coast of New South Wales (NSW) in April and May 2018 and in two adult alpacas from a third property on the Central Coast of NSW in October 2018. Viral RNA was detected in a range of samples, including blood, fresh body organs and mucosal swabs. EMCV was isolated from the blood and body organs of five of these alpacas. These animals displayed a range of clinical signs, including inappetence, colic, recumbency and death. Necropsy findings included multifocal to coalescing areas of myocardial pallor, pulmonary congestion and oedema, hepatic congestion and serosal effusion. Histopathological changes comprised acute, multifocal myocardial degeneration and necrosis, with mild, neutrophilic and lymphocytic inflammation (5/5 hearts) and mild, perivascular neutrophilic meningoencephalitis (1/3 brains). This is the first report of disease due to EMCV in alpacas under farm conditions, and it identifies EMCV infection as a differential diagnosis for acute disease and death in this camelid species. In addition to the samples traditionally preferred for EMCV isolation (fresh heart, brain and spleen), blood samples are also appropriate for EMCV detection by qRT-PCR assay.

Viral Disease

This chapter discusses infections of rats with viruses in the following 14 virus families: Adenoviridae, Arenaviridae, Coronaviridae, Flaviviridae, Hantaviridae, Hepeviridae, Herpesviridae, Paramyxoviridae, Parvoviridae, Picornaviridae, Pneumoviridae, Polyomaviridae, Poxviridae, and Reoviridae . Serological surveys indicate that parvoviruses, coronaviruses, cardioviruses, and pneumoviruses are the most prevalent in laboratory rats. A new polyomavirus and a new cardiovirus that cause disease in laboratory rats are described. Metagenomic analyses of feces or intestinal contents from wild rats have detected viruses from an additional nine virus families that could potentially cause infections in laboratory rats.

A Disintegrin and Metalloproteinase 9 Domain (ADAM9) Is a Major Susceptibility Factor in the Early Stages of Encephalomyocarditis Virus Infection

Encephalomyocarditis virus (EMCV) is a picornavirus that produces lytic infections in murine and human cells. Employing a genome-wide CRISPR-Cas9 knockout screen to find host factors required for EMCV infection, we identified a role for ADAM9 in EMCV infection. CRISPR-mediated deletion of ADAM9 in multiple human cell lines rendered the cells highly resistant to EMCV infection and cell death. Primary fibroblasts from ADAM9 KO mice were also strongly resistant to EMCV infection and cell death. In contrast, ADAM9 KO and WT cells were equally susceptible to infection with other viruses, including the picornavirus Coxsackie virus B. ADAM9 KO cells failed to produce viral progeny when incubated with EMCV. However, bypassing EMCV entry into cells through delivery of viral RNA directly to the cytosol yielded infectious EMCV virions from ADAM9 KO cells, suggesting that ADAM9 is not required for EMCV replication post-entry. These findings establish that ADAM9 is required for the early stage of EMCV infection, likely for virus entry or viral genome delivery to the cytosol.IMPORTANCE Viral myocarditis is a leading cause of death in the United States, contributing to numerous unexplained deaths in people ≤35 years old. Enteroviruses contribute to many cases of human myocarditis. Encephalomyocarditis virus (EMCV) infection causes viral myocarditis in rodent models, but its receptor requirements have not been fully identified. CRISPR-Cas9 screens can identify host dependency factors essential for EMCV infection and enhance our understanding of key events that follow viral infection, potentially leading to new strategies for preventing viral myocarditis. Using a CRISPR-Cas9 screen, we identified a disintegrin and metalloproteinase 9 domain (ADAM9) as a major factor required for the early stages of EMCV infection in both human and murine infection.

Encephalomyocarditis virus is potentially derived from eastern bent-wing bats living in East Asian countries

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EMCV genome was widely found in fecal guanos in Taiwanese, Korean, and Japanese caves.

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Miniopterus fuliginosus is the main source of the fecal guano.

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It is possible that Miniopterus fuliginosus is one of the natural hosts of EMCV in East Asia.

Bats are reservoir hosts of many zoonotic viruses and identification of viruses that they carry is important. This study aimed to use high throughput screening to identify the viruses in fecal guano of Taiwanese insectivorous bats caves in order to obtain more information on bat-derived pathogenic viruses in East Asia. Guano samples were collected from two caves in Taiwan, pooled, and then subjected to Multiplex PCR-based next generation sequencing for viral identification. Subsequently, encephalomyocarditis virus (EMCV) sequence was detected and confirmed by reverse transcription PCR. EMCV is considered as rodent virus and thus, animal species identification through cytochrome oxidase I (COI) barcoding was further done to identify the viral source. Finally, determination of distribution and verification of the presence of EMCV in guano obtained from Japanese and South Korean caves was also done. We concluded that the guano collected was not contaminated with the excrement of rodents which were reported and presumed to live in Taiwan. Also, EMCV genome fragments were found in guanos of Japanese and South Korean caves. It is possible that the eastern bent-wing bat (Miniopterus fuliginosus) is one of the natural hosts of EMCV in East Asia.

Construction, expression, and characterization of a single-chain variable fragment (ScFv) antibody targeting to the encephalomyocarditis virus

Encephalomyocarditis virus (EMCV) is as a potential zoonotic agent with a wide host range. Here, applying gene splicing by overlap extension PCR (SOE-PCR), we describe a simple method for producing single-chain variable fragment (scFv) antibody against EMCV that configurates in the orientation of VH-(GGGGS)₄ -VL. DNA template was resverse transcribed by total RNA that derived from hyperimmunized antibody positive mice spleen after inoculation inactivated EMCV-PV21 as antigen. Using the degenerate primers designed for the variable regions of IgG of murine antibody, the 417 bp of gene encoding VH-linker (VHL) and 360 bp of gene encoding linker-VL (LVL) of the anti-EMCV was individually amplified from DNA template by PCR, repectively. The 762 bp gene encoding anti-EMCV scFv was constructed by SOE-PCR when the mixed VHL and LVL genes were used as the template. The amplified gene subcloned into pGEX-6P1 to yield pGEX-6P1/EMCV-scFv. Recombinant vector transformed into the Escherichia coli BL21 (DE3) and a 53 KDa GST-scFv fusion protein was obtained by SDS-PAGE electrophoresis. Animal experiment results showed that the pretective rate of mice in group A which challenged 500 μL 10⁴ TCID₅₀ EMCV per mouse for 7 d post-inoculation scFv 3 d (0.5 mg purified recombinant scFv per mouse) was 91.67% (11/12). The serum anti-EMCV antibody titer in group A mice was most significantly higher than that in positive control mouse (P < 0.01), coversely the serum relative mRNA copies were significantly lower than that in positive control mouse (P < 0.05). These findings indicated that recombinant anti-EMCV scFv has remarkable anti-EMCV effect in mice.

Development and application of an indirect ELISA for the detection of antibodies against encephalomyocarditis virus

Encephalomyocarditis virus (EMCV) can cause acute myocarditis in young pigs or reproductive failure in sows. It has been recognized worldwide as a pathogen infecting many species and causes substantial economic losses. In the present study, an indirect ELISA was developed for the detection of antibodies to EMCV. The VP1 gene of EMCV was amplified by reverse transcription-quantitative polymerase chain reaction and expressed in Escherichia coli with 49.3 kDa under the condition of isopropyl-β-d-thiogalactoside. Following this, the authors obtained the recombinant protein VP1 as a coating antigen. The antigen concentration and serum dilution were optimized using a checkerboard titration. Compared with viral neutralization tests, the sensitivity and specificity of the indirect ELISA was 95.7% and 92.9%, respectively. A total of 265 clinical swine serum samples from different pig farms in China were used to a serological survey. The seropositive rate of the serum samples was 81.9%. In conclusion, the developed indirect ELISA assay is sensitive and specific, which will be useful for large-scale serological survey in EMCV infection and monitoring antibodies titers against EMCV.

High diversity of picornaviruses in rats from different continents revealed by deep sequencing

Outbreaks of zoonotic diseases in humans and livestock are not uncommon, and an important component in containment of such emerging viral diseases is rapid and reliable diagnostics. Such methods are often PCR-based and hence require the availability of sequence data from the pathogen. Rattus norvegicus (R. norvegicus) is a known reservoir for important zoonotic pathogens. Transmission may be direct via contact with the animal, for example, through exposure to its faecal matter, or indirectly mediated by arthropod vectors. Here we investigated the viral content in rat faecal matter (n=29) collected from two continents by analyzing 2.2 billion next-generation sequencing reads derived from both DNA and RNA. Among other virus families, we found sequences from members of the Picornaviridae to be abundant in the microbiome of all the samples. Here we describe the diversity of the picornavirus-like contigs including near-full-length genomes closely related to the Boone cardiovirus and Theiler's encephalomyelitis virus. From this study, we conclude that picornaviruses within R. norvegicus are more diverse than previously recognized. The virome of R. norvegicus should be investigated further to assess the full potential for zoonotic virus transmission.

Clinical problems due to encephalomyocarditis virus infections in two pig herds

Background

Infections with encephalomyocarditis virus may cause myocarditis and sudden death in young pigs and reproduction disorders in sows. The presence of encephalomyocarditis virus infected rodents is considered a major risk factor for transmission of the virus to pigs. There is currently no effective treatment. Tightening up biosecurity, applying effective rodent control and reducing stress are the main control measures.

Case presentation

Two farrow-to-finish herds suffering from problems with sudden death are presented. In herd A, suckling piglets from 3 to 12 days old were dying acutely whereas in herd B, piglets at the end of the nursery period (8–10 weeks) were showing identical problems. A presumptive diagnosis of encephalomyocarditis virus infection was made because typical lesions were observed in some of the affected pigs. These lesions were not always present in pigs dying acutely or in some cases the lesions were very subtle. Therefore other causes had to be ruled out based upon clinical history, clinical signs and diagnostic tests. A conclusive diagnosis was finally established by showing encephalomyocarditis virus in heart tissue using conventional gel-based polymerase chain reaction tests. The real-time PCR test that gave initially negative result was further optimized to avoid false negative results.

Conclusions

Typical lesions are not always present in piglets infected with encephalomyocarditis virus, indicating the importance of examining multiple animals. Problems in suckling piglets may occur in affected herds without reproductive problems in sows. Transmission routes of EMCV in swine are not fully understood. A stand-empty period following thorough cleaning and disinfection is recommended for controlling EMC virus infections.

The impact of compartmentalised housing on direct encephalomyocarditis virus (EMCV) transmission among pigs; insight from a model

Although generally considered a rodent virus, pigs sometimes were suggested a potential reservoir host for encephalomyocarditis virus (EMCV), implying pig-to-pig transmission can cause major outbreaks in a pig population (basic reproduction ratio, R0>1). An earlier experimental study on EMCV transmission among pigs was inconclusive in this respect (R0≈1.24; CI 0.4-4.4). In this study we used a simulation model to extrapolate the experimental results to commercial, compartmentalised pig housings and tested to what extend contacts between pigs in different pens needed to be reduced in order to prevent major outbreaks in a compartment following a single introduction. The final size of simulated outbreaks was measured and the probability to observe outbreaks that affected at least 50 or 80% of the pens was calculated. Simulation scenarios compare one homogeneously mixing compartment (no fence) to epidemiological theory and an increasing effect of fencing on the pig-to-pig transmission between pigs in neighbouring pens. For any R0<1.24 the probability to observe outbreaks affecting more than 50% of the pens remained below 10% if compartmentalisation was introduced leaving per capita transmission rate unchanged. If fences also reduced contact transmission the probability to observe major outbreaks was below 50% for any R0<2.7. Only for R0>4, major outbreaks occurred with more than 50% chance even if only minimal contact between adjacent pens was allowed. In conclusion the results suggested that in a compartmentalised pig housing one single EMCV introduction is unlikely to cause a major outbreak by direct pig-to-pig transmission alone. Other mechanisms e.g. multiple introductions from a rodent reservoir may be required for large outbreaks to occur.

Development of a TaqMan-based real-time reverse transcription polymerase chain reaction assay for the detection of encephalomyocarditis virus

Encephalomyocarditis virus (EMCV) is one of the major zoonosis pathogens and can cause acute myocarditis in young pigs or reproductive failure in sows. In this study, a TaqMan-based real-time reverse transcription polymerase chain reaction (RT-PCR) assay targeting 3D gene of EMCV was developed and their sensitivities and specificities were investigated. The results indicated that the standard curve had a wide dynamic range (10(1)-10(6) copies/μL) with a linear correlation (R(2)) of 0.996 between the cycle threshold (Ct) value and template concentration. The real-time RT-PCR assay is highly sensitive and able to detect 1.4×10(2) copies/μL of EMCV RNA, as no cross-reaction was observed with other viruses. These data suggested that the real-time RT-PCR assay developed in this study will be suitable for future surveillance and specific diagnosis of EMCV-infection.

Rapid detection of encephalomyocarditis virus by one-step reverse transcription loop-mediated isothermal amplification method

The encephalomyocarditis virus (EMCV) can cause acute myocarditis in young pigs or reproductive failure in sows. In this study, a reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay was developed to detect EMCV RNA. The RT-LAMP assay was highly sensitive and able to detect 2.2 × 10(-5)ng of EMCV RNA, as no cross-reaction was observed with other viruses. The RT-LAMP assay was conducted in isothermal (62 °C) conditions within 50 min. The amplified products of EMCV could be detected as ladder-like bands using agarose gel electrophoresis. This is the first report to demonstrate the application of a one-step RT-LAMP assay for the detection of EMCV. The sensitive, specific and rapid RT-LAMP assay developed in this study can be applied widely in clinical diagnosis and field surveillance of EMCV.

Complete Genome Sequence of Porcine Encephalomyocarditis Virus Strain BD2

Encephalomyocarditis virus (EMCV) causes acute myocarditis in young pigs or reproductive failure in sows, and it is divided into two main groups. Here, we report the complete genome sequence of EMCV strain BD2, which belongs to group I.

Prevalence of swine viral and bacterial pathogens in rodents and stray cats captured around pig farms in Korea

In 2008, 102 rodents and 24 stray cats from the areas around 9 pig farms in northeast South Korea were used to determine the prevalence of the following selected swine pathogens: ten viral pathogens [porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), rotavirus, classical swine fever virus (CSFV), porcine circovirus type 2 (PCV2), encephalomyocarditis virus (EMCV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine parvovirus (PPV), pseudorabies virus (PRV) and Japanese encephalitis virus (JEV)] and four bacterial pathogens (Brucella, Leptospira, Salmonella and Lawsonia intracellularis). In total, 1,260 tissue samples from 102 rodents and 24 stray cats were examined by specific PCR and RT-PCR assays, including tissue samples of the brain, tonsils, lungs, heart, liver, kidneys, spleen, small intestine, large intestine and mesenteric lymph nodes. The percentages of PCR-positive rodents for the porcine pathogens were as follows: 63.7% for Leptospira, 39.2% for Brucella, 6.8% for Salmonella, 15.7% for L. intracellularis, 14.7% for PCV2 and 3.9% for EMCV. The percentages of PCR-positive stray cats for the swine pathogens were as follows: 62.5% for Leptospira, 25% for Brucella, 12.5% for Salmonella, 12.5% for L. intracellularis and 4.2% for PEDV. These results may be helpful for developing control measures to prevent the spread of infectious diseases of pigs.

Occurrence of pathogens in wild rodents caught on Swedish pig and chicken farms

A total of 207 wild rodents were caught on nine pig farms, five chicken farms and five non-farm locations in Sweden and surveyed for a selection of bacteria, parasites and viruses.Lawsonia intracellulariaand pathogenicYersinia enterocoliticawere only detected in rodents on pig farms (9% and 8% prevalence, respectively) which indicate that these agents are more likely to be transmitted to rodents from pigs or the environment on infected farms.Brachyspira hyodysenteriae(1%),Brachyspira intermedia(2%),Campylobacter jejuni(4%),Campylobacter upsaliensis(2%), leptospires (7%) and encephalomyocarditis virus (9%) were also detected from rodents not in contact with farm animals.GiardiaandCryptosporidiumspp. were common, although no zoonotic types were verified, andSalmonella entericawas isolated from 1/11 mice on one farm but not detected by PCR from any of the rodents.Trichinellaspp. andToxoplasma gondiiwere not detected.

The encephalomyocarditis virus

The encephalomyocarditis virus (EMCV) is a small non-enveloped single-strand RNA virus, the causative agent of not only myocarditis and encephalitis, but also neurological diseases, reproductive disorders and diabetes in many mammalian species. EMCV pathogenesis appears to be viral strain- and host-specific, and a better understanding of EMCV virulence factors is increasingly required. Indeed, EMCV is often used as a model for diabetes and viral myocarditis, and is also widely used in immunology as a double-stranded RNA stimulus in the study of Toll-like as well as cytosolic receptors. However, EMCV virulence and properties have often been neglected. Moreover, EMCV is able to infect humans albeit with a low morbidity. 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.

Isolation, molecular characterization, and phylogenetic analysis of porcine encephalomyocarditis virus strain HB10 in China

Encephalomyocarditis virus (EMCV) can cause myocarditis, respiratory failure, reproductive failure, and mortality in pregnant sows, fetuses, and ablactating piglets. Diseases caused by EMCV currently affect the swine industry worldwide. A virus was isolated from organs of dead piglets that presented with acute myocarditis in northern China. The production of a specific cytopathic effect on susceptible cells and the results of hemagglutination inhibition (HI) assay, PCR, electron microscopy (EM), and sequencing indicated that the pathogen was EMCV; the strain was named HB10. Other pathogenic agents causing myocarditis and death were excluded as possible pathogenic agents. Phylogenetic analyses of the capsid coding region and the VP3/VP1 genes using the neighbour-joining method revealed that EMCV isolates cluster into two groups (groups 1 and 2) with two sub-clusters within group 1 (group 1a and b). HB10 belongs to group 1a, along with strains CBNU, GX0601, BJC3, NJ08, and BEL-2887A/91. Five strains isolated from Sus scrofa belong to group 2. The results of this and previous studies indicate that HB10 and other EMCV strains cause myocarditis of pigs in China.

Rodents on pig and chicken farms - a potential threat to human and animal health

Rodents can cause major problems through spreading various diseases to animals and humans. The two main species of rodents most commonly found on farms around the world are the house mouse (Mus musculus) and the brown rat (Rattus norvegicus). Both species are omnivorous and can breed year-round under favourable conditions. This review describes the occurrence of pathogens in rodents on specialist pig and chicken farms, which are usually closed units with a high level of bio-security. However, wild rodents may be difficult to exclude completely, even from these sites, and can pose a risk of introducing and spreading pathogens. This article reviews current knowledge regarding rodents as a hazard for spreading disease on farms. Most literature available regards zoonotic pathogens, while the literature regarding pathogens that cause disease in farm animals is more limited.

Vaccination of llamas, Llama glama, with an experimental killed encephalomyocarditis virus vaccine

Encephalomyocarditis virus (EMCV) is a pandemic virus that has caused mortality in numerous captive wildlife species worldwide. An experimental killed vaccine was created from two EMCV isolates associated with zoo animal mortality in the southern United States. The vaccine was tested for safety and efficacy in eleven llamas (Llama glama). All animals received an initial vaccination and a second booster vaccination 4 wk later. Serum antibody responses were monitored at initial vaccination and at 4 wks, 8 wk, 6 mo, and 12 mo postvaccination. Eight of the 11 llamas vaccinated experienced at least a 4-fold increase in serum antibody titers to EMCV. Antibody titers of those eight animals remained elevated above prevaccination levels when measured at 12 mo. The experimental killed EMCV vaccine tested may be a useful tool to prevent EMCV infection in llamas when given in 2 doses 4 wk apart, and then revaccinated or with antibody levels monitored annually thereafter.

Experimental encephalomyocarditis virus infection in small laboratory rodents

Encephalomyocarditis virus (EMCV) is a cardiovirus that belongs to the family Picornaviridae. EMCV is an important cause of acute myocarditis in piglets and of fetal death or abortion in pregnant sows. Small rodents, especially rats, have been suspected to be reservoir hosts or carriers. This virus also induces type 1 diabetes mellitus, encephalomyelitis, myocarditis, orchitis and/or sialodacryoadenitis in small laboratory rodents. This paper reviews the pathology and pathogenesis of experimental infection with EMCV in small laboratory rodents.

Encephalomyocarditis virus infection in an Italian zoo

A fatal Encephalomyocarditis virus (EMCV) infection epidemic involving fifteen primates occurred between October 2006 and February 2007 at the Natura Viva Zoo. This large open-field zoo park located near Lake Garda in Northern Italy hosts one thousand animals belonging to one hundred and fifty different species, including various lemur species. This lemur collection is the most relevant and rich in Italy. A second outbreak between September and November 2008 involved three lemurs. In all cases, the clinical signs were sudden deaths generally without any evident symptoms or only with mild unspecific clinical signs. Gross pathologic changes were characterized by myocarditis (diffuse or focal pallor of the myocardium), pulmonary congestion, emphysema, oedema and thoracic fluid. The EMCV was isolated and recognized as the causative agent of both outbreaks. The first outbreak in particular was associated with a rodent plague, confirming that rats are an important risk factor for the occurrence of the EMCV infection.

Efficient infection of buffalo rat liver-resistant cells by encephalomyocarditis virus requires binding to cell surface sialic acids

In contrast to the production of virus and cell lysis seen in baby hamster kidney cells (BHK-21) infected with the strain 1086C of encephalomyocarditis virus (EMCV), in buffalo rat liver cells (BRL) neither virus replication nor cytopathic effects were observed. After 29 passages in BRL cells, each alternating with boosts of the recovered virus in BHK-21 cells, the virus acquired the ability to replicate effectively in BRL cells, attaining virus titres comparable to those in BHK-21 cells and producing complete cell destruction. The binding of virus on BRL cells was increased after adaptation and was similar to that observed on BHK-21 cells. Treatment of BRL cells with sialidase resulted in an 87 % reduction in virus binding and inhibition of infection. Sequence analyses revealed three mutations in the VP1 amino acid sequence of the adapted virus at positions 49 (Lys-->Glu), 142 (Leu-->Phe) and 180 (Ile-->Ala). The residue 49 is exposed at the surface of the capsid and is known to be part of a neutralization epitope. These results suggest that the adaptation of EMCV to BRL cells may have occurred through a mutation in a neutralizing site that confers to the virus a capacity to interact with cell surface sialic acid residues. Taken together, these data suggest a link between virus neutralization site, receptor binding and cell permissivity to infection.

Discovery of a novel human picornavirus in a stool sample from a pediatric patient presenting with fever of unknown origin

Fever of unknown origin (FUO) is a serious problem in the United States. An unidentified agent was cultured from the stool of an infant who presented with FUO. This virus showed growth in HFDK cells and suckling mice. Using DNase sequence-independent single-primer amplification, we identified several nucleotide sequences with a high homology to Theiler's murine encephalomyelitis virus. Nearly full-length viral genome sequencing and phylogenetic analysis demonstrate that this virus is a member of the Cardiovirus genus of the Picornaviridae family.

Genomic analysis of two porcine encephalomyocarditis virus strains isolated in China

Two strains of encephalomyocarditis virus (EMCV), designated BJC3 and HB1, were isolated from an aborted fetus and the heart tissue of a dead piglet that had pericardial fluid, respectively. The complete genomic sequences of the two viruses were determined and analyzed. The size of the genomes of BJC3 and HB1 were 7746 and 7735 nucleotides, respectively, including poly(A) tails. Comparative analysis with the genomic sequences of other EMCV strains showed that BJC3 and HB1 shared higher identity (92.5-99.6%) with BEL-2887A/91, EMCV-R and PV21, but lower identity (83.3-84.6%) with EMC-B, EMC-D and D variants, and only 81.0% with Mengo virus. Two amino acid mutations in the leader protein of the two viruses and one amino acid substitution in VP1 of BJC3 were found in comparison to other EMCV strains Phylogenetic analysis based on the amino acid sequences of the entire ORF revealed that the two Chinese isolates BJC3 and HB1 clustered together with the strains BEL-2887/91, EMCV-R and PV21, which belong to the same genetic subgroup as EMCV-30. Our results provide genomic information for EMCV isolated in China.

Factors related to the incidence of clinical encephalomyocarditis virus (EMCV) infection on Belgian pig farms

We set up a matched case-control study of potential risk factors for clinical encephalomyocarditis virus (EMCV) in 58 pig farms in West Flanders (Belgium). In total, 29 farms experienced a clinical outbreak of EMCV confirmed by EMC virus isolation. Mortality was seen only among suckling piglets (18 case farms), in piglets and other age-groups (4 case farms), or only among fattening pigs (7 case farms). Five farms had reproductive problems among the sows. Control farms were matched geographically on farm size and farm type and were selected on the absence of clinical signs. A questionnaire on potential risk factors for EMCV was developed to collect data at both case and control farms. The exploration of the data used clusters of factors associated with clinical EMCV infection: (a) rodents, (b) general farm set up and (c) general hygiene. The multivariable relationships between clinical appearance of EMCV and potential risk factors were tested with conditional logistic regression. The final model on all farms contained presence of mice (OR=8.3) as a risk factor for clinical EMCV infection while the flow of manure up through the slatted floor (OR=0.11) and movement of manure between manure pits in the pig stable (OR=0.14) were protective.

Transmission of encephalomyocarditis virus in pigs estimated from field data in Belgium by means of R0

Transmission of encephalomyocarditis-virus (EMCV) has been estimated in experiments, but never using field data. In this field study, a farm in Belgium was selected where the presence of EMCV was confirmed by necropsy and virus isolation. Serology was used to estimate the transmission parameter R0. In one compartment with 630 pigs, 6 pens were fully sampled, in the remaining 38 pens, 2 randomly selected pigs were bled. The 151 pigs were bled twice and their serum was tested in a virus neutralisation test. Seroprevalence at the first and second sampling was 41 and 43% respectively, with a cut off value of 1:40. R0 was estimated for 2 scenarios, in- and excluding mortality based on the final sizes from the serological results of the second sampling. The R0 for the fully sampled pens was estimated between 0.6 and 1.7, the combined estimated R0 of these 6 pens was 1.36 (95%-CI 0.93-2.23). The median of the estimated R0 of the partially sampled pens was 1.3 and 1.4. Sampling two pigs per pen provided insight into the spread of the virus in the compartment, while the fully sampled pens provided an accurate estimation of R0. The low R0 strongly suggests that EMCV is not very effectively transmitted between pigs. The number of seropositive pigs in a pen and the spread in the compartment suggests that other routes of infection are more important, in this case most likely rodents. Preventing viral spread should therefore be focussed on rodent control instead of reduction of contact between pigs.

Pathogenesis of experimental encephalomyocarditis: a histopathological, immunohistochemical and virological study in rats

Rats (n=40) aged 8 weeks were infected, either by oronasal inoculation or by contact, with one of two different myocardial strains of encephalomyocarditis virus (EMCV), namely, the Greek strain 424/90 and the Belgian strain B279/95. The animals were killed at 11-62 days post-infection (dpi) and samples of brain, heart, pancreas, kidney, Peyer's patches, spleen, lung and thymus were processed for virological, histopathological and immunohistochemical evaluation. This experimental infection was inapparent, but virus was isolated from faeces and several organs of all animals. The main histopathological changes were focal interstitial pancreatitis, degeneration and necrosis of pancreatic acinar cells, depletion of thymus and Peyer's patches, and interstitial pneumonia. EMCV antigen was detected in the cytoplasm of cardiac muscle cells, pancreatic acinar cells and hepatic epithelial cells, and in macrophages of the spleen, lung and thymus. In the heart (the target organ of EMCV in pigs), the presence of EMCV in cardiac muscle cells without lesions lends support to the hypothesis that the rat is a natural reservoir host species of EMCV. The persistence of virus in the macrophages of the thymus may represent a mechanism of perpetuation and reactivation, under immunosuppressive conditions, of the infection.