Encephalomyocarditis Virus Strain Research Articles

RNA sensor–induced type I IFN prevents diabetes caused by a β cell–tropic virus in mice

Viral infections have been linked to the onset of type I diabetes (T1D), with viruses postulated to induce disease directly by causing β cell injury and subsequent release of autoantigens and indirectly via the host type I interferon (IFN-I) response triggered by the virus. Consistent with this, resistance to T1D is associated with polymorphisms that impair the function of melanoma differentiation associated gene-5 (MDA5), a sensor of viral RNA that elicits IFN-I responses. In animal models, triggering of another viral sensor, TLR3, has been implicated in diabetes. Here, we found that MDA5 and TLR3 are both required to prevent diabetes in mice infected with encephalomyocarditis virus strain D (EMCV-D), which has tropism for the insulin-producing β cells of the pancreas. Infection of Tlr3-/- mice caused diabetes due to impaired IFN-I responses and virus-induced β cell damage rather than T cell-mediated autoimmunity. Mice lacking just 1 copy of Mda5 developed transient hyperglycemia when infected with EMCV-D, whereas homozygous Mda5-/- mice developed severe cardiac pathology. TLR3 and MDA5 controlled EMCV-D infection and diabetes by acting in hematopoietic and stromal cells, respectively, inducing IFN-I responses at kinetically distinct time points. We therefore conclude that optimal functioning of viral sensors and prompt IFN-I responses are required to prevent diabetes when caused by a virus that infects and damages the β cells of the pancreas.

Differential IFN-α/β production suppressing capacities of the leader proteins of mengovirus and foot-and-mouth disease virus

Picornaviruses encompass a large family of RNA viruses. Some picornaviruses possess a leader (L) protein at the N-terminus of their polyprotein. The L proteins of encephalomyocarditis virus, a cardiovirus, and foot-and-mouth disease virus (FMDV), an aphthovirus, are both dispensable for replication and their major function seems to be the suppression of antiviral host cell responses. Previously, we showed that the L protein of mengovirus, a strain of encephalomyocarditis virus, inhibits antiviral responses by inhibiting type I interferon (IFN-alpha/beta) gene transcription. The L protein of the FMDV is a protease (L(pro)) that cleaves cellular factors to reduce cytokine and chemokine mRNA production and to inhibit cap-dependent cellular host mRNA translation, thereby limiting the production of proteins with antiviral activity. In this study, we constructed a viable chimeric mengovirus that expresses FMDV L(pro) in place of the authentic L protein in order to compare the efficiency of the immune evasion mechanisms mediated by L and L(pro) respectively. We show that in this mengovirus background the L protein is more potent than FMDV L(pro) in suppressing IFN-alpha/beta responses. Yet, FMDV L(pro) is important to antagonize infection-limiting responses both in vitro and in vivo.

Encephalomyocarditis in Korea: Serological survey in pigs and phylogenetic analysis of two historical isolates

Serum samples from 3315 pigs from 363 farms located throughout all nine Korean provinces were tested for the presence of encephalomyocarditis virus (EMCV) antibodies using the virus neutralization test. The seroprevalence of EMCV in the total pig population was 9.1%, whereas in the herd the prevalence was 43.5%. The first two EMCVs isolated were K3 and K11; these strains were isolated in 1990 from a mummy and a stillborn fetus, respectively, suspected of having EMCV. Phylogenetic analyses of the capsid coding region and the VP3/VP1 genes using the Bayesian approach, and a neighbor-joining analysis, revealed that the EMCV strains fell into two clusters: groups 1 and 2, with two sub-clusters within group 1, group 1a and 1b. The Korean isolates belonged to the group 1a cluster, along with strains BJC3 (China), B424/90 (Greece) and BEL-2887A/91 (Belgium), whereas five strains isolated from Sus scrofa in Belgium (B279/95, B440/95), Italy (I001/96, I136/86), and Cyprus (C108/95) belonged to the group 2 cluster.

Protective immune response in mice vaccinated with a recombinant adenovirus containing capsid precursor polypeptide P1, nonstructural protein 2A and 3C protease genes (P12A3C) of encephalomyocarditis virus

Encephalomyocarditis virus (EMCV) infection can cause acute myocarditis and sudden death in pre-weaned piglets as well as severe reproductive failure in sows. In this study, two recombinant adenoviruses containing capsid precursor polypeptide P1 alone (Ad-P1) and P1 plus nonstructural protein 2A and 3C protease coding regions (Ad-P12A3C) of EMCV were respectively constructed using replication-defective human adenovirus serotype 5 as vector, and their antibody responses and protective efficacies against a lethal EMCV challenge were evaluated in mice. Both Ad-P1 and Ad-P12A3C were confirmed to be capable of expressing VP1 protein in BHK21 cells by immunoperoxidase monolayer assay (IPMA). The results showed that mice vaccinated once or twice with Ad-P1 and Ad-P12A3C generated specific antibody response against VP1 protein of EMCV. Although Ad-P1 induced higher antibody titers, virus-neutralizing antibody response was considerably less (p<0.05), compared to that of Ad-P12A3C. Upon challenging with a virulent EMCV strain, Ad-P12A3C elicited efficacious protection (100% for both vaccination once and twice) in the vaccinated mice; whereas the mice immunized with Ad-P1 showed a lower protection (12.5% for vaccination once and 75% for twice). Our work suggests that the recombinant adenovirus (Ad-P12A3C) containing the capsid precursor polypeptide coding region (P1) plus nonstructural protein 2A and 3C protease genes have an excellent potential to be used as a vaccine that can provide sufficient protective efficacy against EMCV infection in animals.

PDTC inhibits picornavirus polyprotein processing and RNA replication by transporting zinc ions into cells

Previously, it was shown that pyrrolidine dithiocarbamate (PDTC) inhibits proteolytic polyprotein processing and replication of human rhinovirus by transporting metal ions into cells. Here, it is shown that PDTC also inhibits replication of two other picornaviruses: coxsackievirus B3 (CVB3), a closely related virus that belongs to the genus Enterovirus, and mengovirus, an encephalomyocarditis virus strain that belongs to the genus Cardiovirus, and that this inhibition is due to the dithiocarbamate moiety of the compound. Making use of subgenomic replicons, evidence is provided that PDTC inhibits replication of these two viruses by disturbing viral RNA synthesis. Furthermore, it is shown that PDTC transports zinc ions into cells and that these zinc ions play an important role in the antiviral activity mediated by PDTC. Finally, it is shown that PDTC interferes with proteolytic processing of the polyproteins of both CVB3 and mengovirus, but that the underlying mechanism between these two viruses differs. In CVB3-infected cells, PDTC interferes strongly with the proteolytic activity of 3CD(pro), as shown by the impaired production of the mature capsid proteins as well as the autocleavage of 3CD(pro) into 3C(pro) and 3D(pol). In mengovirus-infected cells, however, PDTC had no effect on the proteolytic production of capsid proteins or the autocleavage of 3CD(pro). Instead, PDTC caused the accumulation of a high-molecular-mass precursor protein, due to an impairment in the primary 'break' that normally occurs at the 2A-2B junction. Thus, PDTC disturbs polyprotein processing and replication of two groups of picornaviruses, enteroviruses and cardioviruses, but the underlying mechanism is different.

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.

Cardiovirus leader proteins are functionally interchangeable and have evolved to adapt to virus replication fitness

The leader (L) proteins encoded by picornaviruses of the genus Cardiovirus [Theiler's murine encephalomyelitis virus (TMEV) and Encephalomyocarditis virus (EMCV)] are small proteins thought to exert important functions in virus-host interactions. The L protein of persistent TMEV strains was shown to be dispensable for virus replication in vitro, but crucial for long-term persistence of the virus in the central nervous system of the mouse. The phenotype of chimeric viruses generated by exchanging the L-coding regions was analysed and it was shown that the L proteins of neurovirulent and persistent TMEV strains are functionally interchangeable in vitro and in vivo, despite the fact that L is the second most divergent protein encoded by these viruses after the L* protein. The L protein encoded by EMCV and Mengo virus (an EMCV strain) shares about 35 % amino acid identity with that of TMEV. It differs from the latter by lacking a serine/threonine-rich C-terminal domain and by carrying phosphorylated residues not conserved in the TMEV L protein. Our data show that, in spite of these differences, the L protein of Mengo virus shares, with that of TMEV, the ability to inhibit the transcription of type I interferon, cytokine and chemokine genes and to interfere with nucleocytoplasmic trafficking of host-cell proteins. Interestingly, analysis of viral RNA replication of the recombinant viruses raised the hypothesis that L proteins of TMEV and EMCV diverged during evolution to adapt to the different replication fitness of these viruses.

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.

Pathogenesis of Experimental Encephalomyocarditis: A Histopathological, Immunohistochemical and Virological Study in Mice

Mice (n=20) 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 18-59 days post-infection (dpi), except for two mice that died at 6 and 32 dpi, and samples of brain, heart, pancreas, kidney, Peyer's patches, spleen, lung and thymus were processed for virological, histopathological and immunohistochemical examination. Apart from the two deaths, the experimental infection was inapparent, but virus was invariably recovered from faeces and several organs. The main histopathological lesions were focal interstitial pancreatitis, depletion of thymus and Peyer's patches, and interstitial pneumonia. Additionally, in the two mice that died, multifocal interstitial myocarditis was observed. EMCV antigen was detected in the cytoplasm of pancreatic acinar cells and in macrophages of the lung and the thymus. Antigen was also detected in the cytoplasm of cardiac muscle cells from three animals, including the two that died. The results support the role of mice, in addition to rats, as reservoir hosts in the epidemiology of EMCV infections on pig farms.

Effect of challenge dose and age in experimental infection of pigs with encephalomyocarditis virus

Two experiments were performed to compare the severity of encephalomyocarditis virus (EMCV) infection in pigs. The pigs were challenged with the Greek myocardial strain, at different ages and with different doses. In the first experiment, nineteen susceptible pigs, 40 days old, were divided into three groups and were experimentally infected with 10 6 TCID 50, 10 4 TCID 50 or 10 2 TCID 50 of the Greek EMCV strain. In the second experiment, 10 susceptible pigs, of either 20 or 105 days, were divided into two groups according to age and were experimentally infected with 10 6 TCID 50 of the Greek EMCV strain. In addition, five piglets, each one the same age as its experimental group, were used as uninfected controls. No clinical signs were observed after infection, except a transient temperature rise in some pigs. Another important observation was the difference in mortality between groups. The survival rate of the 40-day-old pigs was inversely related to the viral dose. In these pigs, a positive association between the viral dose and the severity of macroscopical and histopathological lesions of the heart was also evident. Viral isolations from various organs of the challenged 40-day-old pigs increased with the increasing dose level. When challenged with 10 6 TCID 50 of EMCV, there was no difference in the fatality rate of the 20- and 40-day-old pigs, but none of the 105-day-old pigs died. The severity of the macroscopical and the histopathological heart lesions was inversely related to the age of the pigs. Furthermore, viral isolations from the various organs were higher in 20- and 40-day-old pigs than in the older ones. In 40-day-old pigs, neutralizing antibodies linearly increased as the dose increased. These antibodies were consistently lower in 20-day-old pigs. Viraemia, and nasal and faecal excretions were detected in all groups and lasted 1–3 days, except for the 105-day-old pigs whose symptoms lasted for an additional day.

Transmission and pathogenicity of encephalomyocarditis virus (EMCV) among rats.

Due to the probable role played by rodents as a reservoir for the transmission of the EMC virus to pigs, the experiment reported here was performed in order to assess the transmission rate of EMCV within a rat population. Twenty-five eight-week-old Wistar rats housed in individual plastic cages were experimentally infected either with a Greek myocardial EMCV strain (5 rats with a 0.2 x 10(6) TCID50 dose per rat and 10 rats with a 0.5 x 10(4.5) TCID50 dose per rat, oronasally) or a Belgian myocardial EMCV strain (10 rats with a 0.5 x 10(4.5) TCID50 dose per rat, oronasally). Two to five days later, each inoculated rat was moved to a new clean cage and coupled with a contact rat to compare the pathogenicity of the two strains and to estimate the basic reproduction ratio R0, indicating the level of EMCV transmission. During the experiments, faecal virus excretion was measured as well as the serological response against EMCV. After euthanasia, virus isolation was attempted from different rat tissues. Neither strains produced mortality, nor clinical signs and only low titres of neutralising antibodies were found. All contact rats, however, were infected and the virus was isolated from their faeces and from various tissues. Both 10-pair experiments revealed a point estimate for the R0 of infinity (95%-CI for both the Greek and Belgian EMCV strains = 4.48 - infinity), as did the 5-pair experiment with a higher dose of the Greek strain (95%-CI = 1.83 - infinity). Combining the results from the two 10-pair experiments resulted in an estimate for R0 of infinity (95%-CI: 9.87 - infinity). These results indicate that the EMC virus can spread very easily within a rat population by horizontal rat-to-rat transmission (R0 >> 1).

Pathogenesis of Encephalomyocarditis Virus (EMCV) Infection in Piglets during the Viraemia Phase: a Histopathological, Immunohistochemical and Virological Study

Six piglets aged 20 days were inoculated oranasally with 5 ml of a suspension (10 6 TCID 50/ml) of a Greek myocardial strain of encephalomyocarditis virus (EMCV). The animals either died ( n=2) or were killed for examination on days 1,2 or 3 post-inoculation (pi). EMCV was isolated from virtually all organs examined (heart, tonsils, palatine glands, pancreas, spleen, small intestine and mesenteric lymph nodes). Histopathologically, interstitial myocarditis, necrosis of cardiac muscle cells and Purkinje fibres, and necrotizing tonsillitis were detected in all inoculated piglets. Focal interstitial pancreatitis, necrosis of pancreatic acinar cells and Langerhans islet cells, and necrosis of germinal centre lymphocytes of the lymph nodes and Peyer's patches were detected in two piglets that died or were killed on day 3 pi. Immunohistochemically, viral antigen was detected in epithelial cells of all organs examined, including the tonsils, palatine glands, pancreatic interlobular ducts and small intestine. This suggests that EMCV is epitheliotropic, in addition to its known myocardial tropism. The frequent presence of intracytoplasmic EMCV in macrophages of the tonsils and spleen supports the hypothesis that macrophages play a role in viral replication and dissemination in the body.

Transmission of encephalomyocarditis virus (EMCV) among pigs experimentally quantified

Two types of transmission experiments were performed to estimate the basic reproduction ratio R 0, indicating the level of encephalomyocarditis virus (EMCV) transmission among pigs. In a first experimental set-up with nine separate pairs, one randomly chosen piglet per pair was inoculated with a Belgian (myocardial) EMCV strain (B279/95, 10 3 TCID 50/ml oronasally) and placed back into the pen. In the second experiment with two separate groups of five piglets, two piglets in each group were inoculated at the start. During the experiments, viraemia in blood and excretions was measured as well as the serological response against EMCV antigen. After death or euthanasia, the piglets were checked for heart lesions and virus isolation was done on various tissues. In both the experiments, the majority of the inoculated piglets either died with typical heart lesions (five out of nine and three out of four resp.), or produced high levels of neutralising antibody. EMC virus was isolated from the hearts of all piglets that died during either one of the experiments. The pairwise experiment revealed a point estimate for R 0 of 2.0 (95% confidence interval (CI)=0.37–10.74), while the group experiment resulted in a R 0-value of 0.71 (95% CI=0.08–4.93). Combining the information from both experiments results in an estimate for R 0 of 1.24 (95% CI=0.39–4.35). Since R 0 has values around the threshold value of 1, the spread of EMCV due to contacts between pigs will in most cases be limited, but due to chance processes may lead to large outbreaks as well.

Nucleotide sequence and construction of an infectious cDNA clone of an EMCV strain isolated from aborted swine fetus

A full-length cDNA clone of an Encephalomyocarditis virus (EMCV) strain (2887A) isolated from aborted swine fetus was constructed and sequenced. Sequence comparison showed more than 99% nucleotide and amino acid sequence identity with two other EMCV strains, EMCV-PV21 and -R. However, the 2887A genomic sequence showed only about 84% nucleotide identity and 96% amino acid identity with EMCV-B, -D and -PV2 variants. RNA synthesized by in vitro transcription of this cDNA clone was infectious upon transfection of BHK21 cells, as shown by cytopathic effects and identification by neutralization test, and by propagation of the virus released into the culture media. The transcript RNA led to the production of infectious particles despite the presence of two nongenomic nucleotide residues at the 5′ end, the short poly(C) tract (C 10TCTC 3TC 10), the short poly(A) tail (7A), and the presence of six nongenomic nucleotides at the 3′ end. The rescued virus was also found to be highly pathogenic for mice by intra-peritoneal inoculation producing a fatal disease indistinguishable from that of wild-type virus. An important finding concerning the molecular basis of infectivity was that the in vitro synthesized EMCV RNA transcript is infectious, although it contains a very short poly(A). The availability of the infectious cDNA clone of the reproductive failure strain of EMCV should prove to be useful for studying the molecular basis of the pathogenicity of EMCV in pig.

Genetically engineered Mengo virus vaccination of multiple captive wildlife species.

Encephalomyocarditis virus (EMCV), has caused the deaths of many species of animals in zoological parks and research institutions. The Audubon Park Zoo, (New Orleans, Louisiana, USA) attempted vaccination of several species with a killed EMCV vaccine with mixed results. This paper reports an attempt at vaccination against EMCV using a genetically engineered, live attenuated Mengo virus (vMC0) at the Audubon Park Zoo and Miami Metro Zoo, (Miami, Florida, USA) from December 1996 to June 1997. Several species of animals were vaccinated with vMC0, which is serologically indistinguishable from the field strain of EMCV. Serum samples were taken at the time of vaccination and again 21 days later, then submitted for serum neutralization titers against EMCV. The vaccinate species included red capped mangebey (Cercocebus torquatus), colobus (Colobus guereza), angolan colobus (Colobus angolensis), ruffed lemur (Lemur variegatus ruber and Lemur variegatus variegatus), back lemur (Lemur macaco), ring-tailed lemur (Lemur catta), siamang (Hylobates syndactylus), diana guenon (Cercopithicus diana), spider monkey (Ateles geoffroyi), common marmoset (Callithrix jacchus), talapoin monkey (Cercopithecus talapoin), Brazilian tapir (Tapirus terrestris), Baird's tapir (Tapirus bairdii), Malayan tapir (Tapirus indicus), dromedary camel (Camelus dromedarius), bactrian camel (Camelus bactrianus), gerenuk (Litocranius walleri), guanaco (Lama glama guanicoe), black duiker (Cephalophus niger), Vietnamese potbellied pig (Sus scrofa), babirusa (Babyrousa babyrussa), collard peccary (Tayass tajacu), and African crested porcupine (Hystrix africaeaustralis). The vaccine response was variable, with high virus neutralizing antibody titer responses in some primate species and mixed to poor responses for other species. No ill effects were seen with vaccination.

Cytokines produced early in picornavirus infection reflect resistance or susceptibility to disease.

Gender bias favoring female resistance to picornavirus disease is not seen in ICR Swiss mice following infection with the MM strain of encephalomyocarditis virus (EMCV) (causing encephalitis and death) as it is with D variant of EMCV (causing diabetes in males). To define this difference, an in vitro virus-infected splenocyte culture system was used to explore virus effects on lymphoid cells. Infected and sham-infected splenocyte cultures, prepared from both genders of mice and infected with either virus variant, were examined for immunoregulatory cytokines in the first 24 h of infection using ELISA or bioassays. Disease resistance was associated with increased levels of interferon-y (IFN-gamma) and undetectable levels of interleukin-10 (IL-10) by 12 h postinfection in splenocytes from ICR Swiss females infected with EMCV-D. Disease susceptibility was associated with high levels of IL-10 at 12 h after infection of spleen cells from ICR Swiss males infected with EMCV-D or from both genders infected with EMCV-MM. This information was used to protect susceptible mice against picornavirus disease (either diabetes or death) by giving them an inducer of IFN-alpha/beta, to induce natural killer (NK)-like cells to produce high levels of IFN-gamma and rat monoclonal anti-IL-10 to neutralize the effects of mouse IL-10.

Rapamycin and wortmannin enhance replication of a defective encephalomyocarditis virus.

Inhibitors of the phosphatidylinositol 3-kinase (PI3 kinase)-FKBP-rapamycin-associated protein (FRAP) pathway, such as rapamycin and wortmannin, induce dephosphorylation and activation of the suppressor of cap-dependent translation, 4E-BP1. Encephalomyocarditis virus (EMCV) infection leads to activation of 4E-BP1 at the time of host translation shutoff. Consistent with these data, rapamycin mildly enhances the synthesis of viral proteins and the shutoff of host cell protein synthesis after EMCV infection. In this study, two defective EMCV strains were generated by deleting portions of the 2A coding region of an infectious cDNA clone. These deletions dramatically decreased the efficiency of viral protein synthesis and abolished the virus-induced shutoff of host translation after infection of BHK-21 cells. Both translation and processing of the P1-2A capsid precursor polypeptide are impaired by the deletions in 2A. The translation and yield of mutant viruses were increased significantly by the presence of rapamycin and wortmannin during infection. Thus, inhibition of the PI3 kinase-FRAP signaling pathway partly complements mutations in 2A protein and reverses a slow-virus phenotype.

Encephalomyocarditis viruses with short poly(C) tracts are more virulent than their mengovirus counterparts.

We have constructed three cDNA clones of encephalomyocarditis virus strain R (EMCV-R) with poly(C) tracts of C4, C9, and C20. RNA transcribed from these cDNAs was infectious to HeLa cells, and the resultant viruses grew well in this system, albeit with plaque sizes that were proportional to the poly(C) length. When injected into mice, the progeny viruses were only slightly less pathogenic than EMCV-R, and the observed degree of attenuation was not nearly as dramatic as for equivalent mengoviruses with similar short poly(C)s. Short-tract poly(C)-mediated attenuation is therefore highly dependent on viral genomic context.

Development of a radiolabeled nucleic acid probe for the detection of encephalomyocarditis virus of swine.

Encephalomyocarditis virus (EMCV) is a member of the genus Cardiovirus of the family Picomaviridae and infects a number of species including mice, elephants, squirrels, swine, and humans. EMCV infections in swine are usually sporadic in nature throughout the world. EMCV causes encephalitis and myocarditis with high mortality in young piglets and has also been associated with maternal reproductive disease in swine. 4,15,16,19 Transplacental infection in pregnant sows has been demonstrated, but the role of EMCV in clinical reproductive disease in the US swine herds is unclear. Serologic evidence of EMCV infection in swine without clinical problem has been reported. 22 Serologic data suggest that EMCV infections are widespread in the US swine herds, but EMCV has been isolated from only a limited number of cases. 10-14,26 Whether the poor success in EMCV isolation from aborted fetuses is due to the lability of EMCV or to the lack of any role of EMCV in swine reproductive disease has not been resolved. The presence of blocking antibodies may also interfere with the isolation of EMCV from clinical specimens. The recent isolation of porcine reproductive and respiratory syndrome (PRRS) virus from herds with reproductive failure has further confused what role EMCV has in swine reproductive failure in the US swine herds. EMCV isolates are closely related antigenically and there is probably only 1 serotype of EMCV. Variants of EMCV have been isolated that differ in organ tropism and pathogenicity. 1 Antigenic and genomic variability among various EMCV strains has also been reported and may be associated with the diversity in pathogenicity. 1,7,11,24,24 VP1 is the major polypeptide of EMCV against which virus neutralizing antibodies are directed. The VP1 gene is also the least conserved capsid gene among different members of Picornavirus. In contrast, the VP3 and VP4 genes and the 5' nontranslated region of EMCV are more conserved. 13,14,20,26 The major objective of the present study was to determine whether a nucleic acid probe specific for EMCV infection in swine could be developed. Such a probe would be useful in determining the prevalence and role of EMCV, if any, in swine reproductive failure. The EMCV strains used for this study were NVSL-FL, MN-25, ATCC VR-129B, Georgia, OVL-5/90, and Mengo. The NVSL-FL strain was isolated initially from pigs in Florida. The MN-25 strain was isolated from an aborted swine fetus obtained from a Minnesota farm that had a history of acute reproductive failure and neonatal losses. The ATCC VR-129B was originally isolated from a chimpanzee

Outbreaks in Quebec pig farms of respiratory and reproductive problems associated with encephalomyocarditis virus.

Encephalomyocarditis virus (EMCV) was isolated from tissues of aborted fetuses and weaned and suckling piglets from 4 different pig farms in Quebec. The farms were experiencing reproductive failure in sows of different parities concomitant to respiratory problems in suckling and postweaning piglets. At necropsy, gross lesions were confined to the lung and consisted of pulmonary congestion and edema of various degrees. Lesions of multifocal interstitial to proliferative pneumonia were found in the lungs of these piglets. Bacteriologic examination of various tissues from necropsied pigs yielded no pathogens in most cases. No significant antibody titers against 3 swine viruses (transmissible gastroenteritis virus, porcine parvovirus, and swine influenza virus) and two bovine viruses (bovine viral diarrhea and infectious bovine rhinotracheitis viruses) were detected in the sera of convalescent pigs. The Quebec EMCV isolates were antigenically related to the reference ATCC-VR129 strain of EMCV, as demonstrated by indirect immunofluorescence, serum neutralization (SN), and Western immunoblotting. However, one of the Quebec isolates could be distinguish by SN. EMCV-specific SN antibody titers up to 1:12,800 were detected in thoracic and ascitis fluids of aborted fetuses and in sera of convalescent pigs. A possible pneumotropic EMCV variant in swine may exist.