Fatal inflammatory heart disease in a bonobo (Pan paniscus)

We report the first probable identification of encephalomyocarditis virus (EMCV) in a bonobo (Pan paniscus) that had been part of a forest re-introduction programme. Clinical presentation was of episodic acute on chronic heart failure and cerebral infarction with end-stage renal failure rather than sudden death which is more commonly associated with EMCV infection. A postmortem diagnosis of probable EMCV was made using gross pathological and histopathological examination. Findings included acute on chronic heart failure combined with the unusual but characteristic histopathological features of non-suppurative necrotizing myocarditis with mononuclear, inflammatory infiltration of the brain.

Encephalomyocarditis in Monkeys

This paper presents the results of studies of a spontaneous viral infection in monkeys--encephalomyocarditis caused by encephalomyocarditis virus. The infection first detected in the Sukhumi Breeding Center in 1974 was observed in the Adler Breeding Center since 2001. The characteristics of the virus are described and principles of diagnostic by the results of pathologic studies are presented.

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).

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.

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.

Detection of encephalomyocarditis virus in clinical samples by immunomagnetic separation and one-step RT-PCR

A method of immunomagnetic separation and one-step reverse transcription-polymerase chain reaction (RT-PCR) was developed for the detection of Encephalomyocarditis virus (EMCV). EMCV was captured from sample on magnetic beads with homologous monoclonal antibody and then heat denatured. The heated beads were used directly in one-step RT-PCR reaction to amplify a 285-bp PCR fragment at the 3' end of the genomic region that encodes the viral polymerase. This method detected as little as 3.5 TCID(50) of EMCV from infected cell culture. It was shown with this method that the sensitivity of RT-PCR increased when applied for the detection of EMCV added to fecal extract. Using this protocol EMCV was detected from heart homogenate samples containing less than 100 TCID(50)/ml. The amplified product was sequenced to ensure specificity. The immunomagnetic-RT/PCR procedure described here should be useful for the rapid, specific and sensitive detection of EMCV in clinical samples. This technique is rapid, reliable and can be readily adapted to detect EMCV from other clinical samples.

Serological evidence that Mus musculus is the natural host of Theiler's murine encephalomyelitis virus

Theiler's murine encephalomyelitis virus (TMEV) infection is maintained in mouse colonies by fecal-oral spread (with no apparent role for persistent central nervous system infection) from an acutely infected animal to another. Therefore, serological methods offer the principal way to assess infection in mice and related rodent populations. Infection of mouse colonies with TMEV appears to be worldwide, yet no systematic serologic studies have been reported. In this study, enzyme-linked immunoassay and neutralization analysis of sera from feral Mus musculus obtained from four locations in the United States and one in Russia revealed antibodies to purified TMEV and two linear viral peptide epitopes in more than 50% of the sera derived from the five different locations. A similar analysis of sera from 26 species of related rodents trapped at multiple locations in North America and Europe indicated the presence of anti-TMEV antibodies only in a small proportion of water and bank voles that belong to a different subfamily. These results indicate that Mus musculus is the natural host of TMEV.

Evaluation of ultrastructural changes associated with encephalomyocarditis virus in the myocardium of experimentally infected piglets

OBJECTIVE

To evaluate the ultrastructural changes and localization of encephalomyocarditis virus (EMCV) and viral pathogenesis in the myocardium of experimentally infected piglets.

ANIMALS

Eight 20-day-old piglets.

PROCEDURE

Six piglets were inoculated oronasally with 5 ml (10(6) median tissue culture infective dose/ml) of EMCV suspension, and 2 were used as uninfected controls. Piglets were euthanatized or died between postinoculation days 1 and 3. Samples of heart tissue from all piglets were evaluated histologically, by virus isolation, and by use of immunohistochemistry and electron microscopy.

RESULTS

All infected piglets had gross or microscopic lesions of interstitial myocarditis. immunohistochemically, EMCV antigen was detected in the cytoplasm of cardiac muscle cells, Purkinje fibers, and endothelial cells and in the nucleus of cardiac muscle cells and Purkinje fibers. Ultrastructural lesions were characterized by degeneration and necrosis of cardiac muscle cells and Purkinje fibers. Virus was present intracytoplasmically in cardiac muscle cells, Purkinje fibers, and endothelial cells of capillaries and intranuclearly in cardiac muscle cells. The cell membranes of the Purkinje fibers and endothelial cells had distinct protrusions that contained virus particles. In control piglets, no lesions were found, and no EMCV antigen was detected.

CONCLUSIONS

Localization of EMCV intracytoplasmically or intranuclearly in various myocardial cells may well reflect the sites of viral proliferation. The presence of virus particles in cell membrane protrusions and in vacuoles within the lumen of capillaries indicates that virus is released not only by disintegration of the host cell but also via exocytosis.

Persistence of encephalomyocarditis virus (EMCV) infection in piglets

Six piglets that had survived experimental infection with encephalomyocarditis virus (EMCV) were treated with dexamethasone for a period of 5 days. The virus had not been detected in excretions of putative carriers for a period of 13-20 days before the treatment. All piglets showed a rise in cardiac isoenzyme (CK-MB) activity, from the first day of treatment, suggesting myocardial damage. Antibody titres against EMCV remained stable or slightly decreased during treatment. EMCV was isolated from blood, nasal and faecal samples from all piglets on days 2 and 3 after initiation of treatment and from various tissues of three piglets. Four contact piglets, that were housed together with the dexamethasone-treated piglets, became infected, indicating that EMCV was shed by treated piglets. It is suggested that recovered pigs may play an important role in the dissemination of EMCV.

A comparative study of the pathogenic properties and transmissibility of a Greek and a Belgian encephalomyocarditis virus (EMCV) for piglets

Thirteen susceptible piglets, aged 40 days, were divided into two groups and were experimentally infected either with a Greek (myocardial) or a Belgian (reproductive) encephalomyocarditis virus (EMCV) strain (total dose 5 x 10(6) TCID50, intramuscularly and intranasally). Six piglets were placed in the same rooms, 24 h later, as contact controls. The following criteria were studied: ante mortem: clinical signs, serum cardiac isoenzyme activities (CK-MB and LD-1), viraemia, nasal and faecal virus excretion and serological response. Post mortem (after death or euthanasia): gross lesions, virus isolation from tissues, RT-PCR, as well as histopathological and immunohistochemical findings. The Greek strain was more pathogenic, producing mortality, with high cardiac isoenzyme activities and pronounced macroscopic myocardium lesions. The Belgian strain was able to induce mild heart lesions, as detected only by cardiac isoenzyme activity and histopathologically. All contact pigs were infected, within the first 1-2 days of their introduction, that coincided with the period of viral excretion by the experimentally infected pigs (up to the 3rd day post infection). Disease was mild, with no mortality.

Epidemiologic, pathogenic and molecular analysis of recent encephalomyocarditis outbreaks in Belgium

In 1991 EMCV was isolated for the first time in Belgium from the offspring of a sow with reproductive failure. From August 1995 until December 1996, EMCV was diagnosed in 154 Belgian pig holdings in association with myocardial failure and sudden death in fatteners and suckling piglets or with reproductive failure in sows. To clarify some epidemiological aspects 3 EMCV isolates characteristic for the different clinical pictures and outbreaks were studied. Field observations and animal experiments indicated that the pathogenicity induced by each isolate is specific for one age category and that the spread of the virus is limited. The presented data also suggest that rodents may play a role in the transmission of EMCV but that pig-to-pig transmission is at least as important. Molecular analysis of two separate regions on the genomes of the respective EMCV isolates showed that the 1995-96 EMCV epizootic in Belgium was due to a new virus introduction. Furthermore, the VP1 coding gene is proposed as a marker of virulence.

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.

Molecular analysis of encephalomyocarditis viruses isolated from pigs and rodents in Italy

Partial nucleotide sequences of encephalomyocarditis (EMC) viruses isolated from five, apparently independent, outbreaks of fatal myocarditis in pigs in Italy were compared with three EMC viruses isolated from wild rodents from a different geographic region in the same country. These viruses were also compared with EMC viruses isolated from pigs in other European countries and three historical strains. All the Italian EMC viruses were closely related (> 94.6% nucleotide identity), but were distinct from viruses occurring in Belgium in 1991 (< 80.5% nucleotide identity), Greece in 1990 (< 83.3% nucleotide identity) and the three older viruses (< 82.9% nucleotide identity). An EMC virus isolated from pigs in the Netherlands in 1988, was closely related to the Italian viruses (95.3-99.3% nucleotide identity). It is suggested that pigs may play a role in the movement of EMC viruses between different geographic regions.

Genetics of susceptibility to Theiler's virus infection

Theiler's virus is a picornavirus of mouse which causes an acute encephalomyelitis followed by a persistent infection of the white matter resulting in chronic inflammation and demyelination. This disease has been studied as a model for multiple sclerosis. Inbred strains of mice are either resistant--they clear the infection after the acute encephalomyelitis--or susceptible to persistent infection and demyelination. Susceptibility is a polygenic trait which has been analyzed using methods of association with "candidate" genes, and linkage analysis after a complete genome scan. The H-2Db gene is responsible for an efficient CTL response which makes some strains resistant. Non H-2 genes responsible for the susceptibility of other strains have been mapped by linkage analysis to the lfng and, possibly, the Mbp loci. The analysis of a set of congenic mice ruled out the possibility that the relevant gene codes for interferon gamma, and showed that the region around lfng probably contains two susceptibility genes. The analysis of mutant mice showed further that the Mbp gene, which codes for the myelin basic protein, has a major effect on viral persistence.

The efficacy of an experimental oil-adjuvanted encephalomyocarditis vaccine in elephants, mice and pigs

An oil-adjuvanted inactivated encephalomyocarditis (EMC) vaccine was developed to protect a wild population of elephants against a natural outbreak of disease. The experimental vaccine was initially tested for efficacy by challenging mice and pigs. Mice showed protection against challenge and pigs developed high antibody levels. Since both vaccinated and control pigs failed to develop clinical disease, apparently due to the low virulence of the strain in this species, protection in pigs could not be evaluated. Vaccinated elephants developed high antibody titers which protected all vaccinates from a challenge roughly two months post-vaccination, whereas controls developed fatal or sub-clinical myocarditis. This is the first report of an inactivated EMC vaccine inducing high antibody titers in domestic and wild animal species. Due to the potency of this vaccine and the acceptability of the oil adjuvant used, it has potential for use in animals in zoological collections as well as in the pig industry.

Comparative study of the pathogenic properties of a Belgian and a Greek encephalomyocarditis virus (EMCV) isolate for sows in gestation

Thirteen conventional sows were inoculated between 61 and 92 days of gestation with a Belgium or a Greek EMCV isolate to investigate the difference in pathogenicity of both strains for sows in gestation. The Belgian EMCV strain was isolated from the offspring of a sow with productive failure and without myocardial lesions. The Greek strain was isolated from a 3-month-old pig with prominent myocardial lesions. The present study demonstrates a transplacental virus transmission with fetal death following an infection of the sows in gestation with both isolates. The fetal pathogenicity was more severe with the Greek strain than with the Belgian isolate. No myocardial lesions were noticed.

Rapid diagnosis of encephalomyocarditis virus infections in pigs using a reverse transcription-polymerase chain reaction

Encephalomyocarditis virus (EMCV) is widespread and the economic losses caused by an EMCV outbreak in pig holdings and the similarity between a foot-and-mouth disease virus (FMDV) and an EMCV infection in young piglets stress the need for a rapid, specific and broad diagnostic assay. An alternative to the time-consuming seroneutralisation assay, currently used for the characterisation of EMCV, is described. An EMCV specific reverse transcription-polymerase chain reaction (RT-PCR), using primers located in a conserved region of the 3D gene of the viral genome, was developed and tested on 114 different EMCV isolates. The identity of the respective amplicons was confirmed by sequencing. The potential of this assay for future diagnostic purposes was demonstrated by applying the RT-PCR on tissue samples collected from an experimentally infected piglet.

Encephalomyocarditis virus infections in an Australian zoo

Fatal encephalomyocarditis virus (EMCV) infections in a ring-tailed lemur (Lemur catta), a squirrel monkey (Saimiri sciureus), three mandrills (Mandrillus sphinx), a chimpanzee (Pan troglodytes), a pygmy hippopotamus (Choeropsis liberiensis), and two Goodfellows tree kangaroos (Dendrolagus goodfellowi) occurred at Taronga Zoo. This is the first description of EMCV in a zoological collection outside of the United States. Regardless of species, the most common clinical presentation was sudden death. The gross pathologic changes were diffuse or focal pallor of the myocardium with occasional marked pulmonary congestion. Necrotizing nonsuppurative myocarditis was consistently present. EMCV was isolated from only one of 54 feral rodents examined. No antibodies to EMCV were detected with a serum neutralization test in 79 stored sera from a wide variety of zoo mammals. Titers of 1:16, 1:16, and 1:4 were recorded for a spider monkey (Aeteles geoffroyi), a lion (Panthera leo), and an orangutan (Pongo pygmaeus), respectively. Of seven mandrills tested in 1988, six had measurable virus titers. Later testing indicated that these titers did not persist, and one mandrill with a titer > 1:128 in 1988 subsequently succumbed to EMCV infection in 1991.

Comparison of the pathogenic, antigenic and molecular characteristics of two encephalomyocarditis virus (EMCV) isolates from Belgium and Greece

The pathogenicity of two porcine encephalomyocarditis virus (EMCV) isolates for sows in gestation and young piglets was studied. One virus originated from a case of reproductive failure in pigs in Belgium and the other from a case of acute myocarditis in pigs in Greece. Sows in the mid-gestation period and one- to two-month old piglets were inoculated with each isolate. The molecular relationship between both isolates was studied by determining the nucleotide sequence located across the junction of the 1C and 1D capsid-coding genes. Antigenic analysis was performed using a panel of 35 monoclonal antibodies raised against an Italian field isolate of EMCV. All three approaches revealed differences between both isolates and also confirmed that there was no link between the two outbreaks of disease.

Antibody responses to two encephalomyocarditis virus vaccines in rhesus macaques (Macaca mulatta)

Two groups of rhesus macaques (Macaca mulatta) housed in rodent-controlled outdoor corrals were inoculated with two different encephalomyocarditis virus (EMCV) vaccines. One group (n = 45) received a vaccine made from an inactivated field isolate of virus cultured during an outbreak at a zoo in Florida. This vaccine produced fourfold increases in the titers of 28 animals (62%); the increases persisted for at least 18 months (last test) after a single injection of the vaccine. The other group (n = 51) received a vaccine made from an inactivated porcine field strain of the virus. This vaccine did not produce titers in any of the vaccinees.

A retrospective serological survey of the encephalomyocarditis virus among pigs in Chiba prefecture, Japan

One thousand two hundred and forty pigs' sera collected from 1975 to 1992 on 240 farms in Chiba prefecture were subjected to a neutralization test for the encephalomyocarditis (EMC) virus. Seven (23.3%) of 30 pigs in 1975 had neutralizing antibodies against the EMC virus. The antibody positive rates each year ranged from 16.7% (1976) to 56.3% (1981). The differences of antibody positive rates between districts were not great after 1985. These serological results suggested that the EMC virus infection had already been introduced by 1975 and that it is prevalent among pigs in Chiba prefecture.

An outbreak of encephalomyocarditis-virus infection in free-ranging African elephants in the Kruger National Park

A cluster of four deaths in late December 1993, marked the onset of an outbreak of disease of African elephants (Loxodonta africana) in the Kruger National Park (KNP) in South Africa, which has an estimated population of 7,500 elephants. Mortalities peaked in January 1994, with 32 deaths, and then declined steadily to reach pre-outbreak levels by September, but sporadic losses continued until November. During the outbreak altogether 64 elephants died, of which 53 (83%) were adult bulls. Archival records revealed that, in addition to the usual losses from known causes such as poaching and intraspecific fighting, sporadic deaths from unexplained causes had, in fact, occurred in widely scattered locations from at least 1987 onwards, and from that time until the perceived outbreak of disease there had been 48 such deaths involving 33 (69%) adult bulls. Carcases had frequently become decomposed or had been scavenged by the time they were found, but seven of eight elephants examined early in 1994 had lesions of cardiac failure suggestive of encephalomyocarditis (EMC)-virus infection, and the virus was isolated from the heart muscles of three fresh carcases. The results of tests for neutralizing antibody on 362 elephant sera collected for unrelated purposes from 1984 onwards and kept frozen, indicated that the virus had been present in the KNP since at least 1987. Antibody prevalences of 62 of 116 (53%) 18 of 139 (13%) and seven of 33 (21%) were found in elephants in three different regions of the KNP in 1993 and 1994. Studies had been conducted on myomorph rodents in the KNP for unrelated purposes since 1984, and trapping attempts were increased during the perceived outbreak of disease in elephants. There was a striking temporal correlation between the occurrence of a population explosion (as evidenced by markedly increased catch rates per trap-night) and a surge in prevalence of antibody to EM virus in rodents, and the occurrence of the outbreak of disease in elephants.