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

The complex interplay between encephalomyocarditis virus and the host defence system

A variety of animals can be infected by encephalomyocarditis virus (EMCV). EMCV is the established causative agent of myocarditis and encephalitis in some animals. EMCV causes high fatality in suckling and weaning piglets, making pigs the most susceptible domestic animal species. Importantly, EMCV has zoonotic potential to infect the human population. The ability of the pathogen to avoid and undermine the initial defence mechanism of the host contributes to its virulence and pathogenicity. A large body of literature highlights the intricate strategies employed by EMCV to escape the innate immune machinery to suit its "pathogenic needs." Here, we also provide examples on how EMCV interacts with certain host proteins to dampen the infection process. Hence, this concise review aims to summarize these findings in a compendium of decades of research on this exciting yet underappreciated topic.

Construction, expression and assemble of EMCV VLPs and their potency evaluation

Encephalomycarditis virus (EMCV) is an essential pathogen with a broad host range and causes enormous economic losses to the pig industry worldwide. Here, we constructed and assembled the EMCV virus-like particles (VLPs) in vitro and verified high efficiency of virus protection. Results showed that the proteins auto-assembled into VLPs successfully in vitro. The animal experiments revealed that high-titer antibody production is triggered by VLPs. Meanwhile, the mice challenged with EMCV were obviously protected. The protection rate of group VLPs with the adjuvant was 75%, while that of the VLPs group was 62.5% compared to the control. These findings indicate that recombinant EMCV VLPs have a remarkable anti-EMCV effect and could be a new vaccine candidate for the control of EMCV infection.

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.

Encephalomyocarditis Virus Abrogates the Interferon Beta Signaling Pathway via Its Structural Protein VP2

Type I interferon (IFN)-mediated antiviral responses are critical for modulating host-virus responses, and indeed, viruses have evolved strategies to antagonize this pathway. Encephalomyocarditis virus (EMCV) is an important zoonotic pathogen, which causes myocarditis, encephalitis, neurological disease, reproductive disorders, and diabetes in pigs. This study aims to understand how EMCV interacts with the IFN pathway. EMCV circumvents the type I IFN response by expressing proteins that antagonize cellular innate immunity. Here, we show that EMCV VP2 is a negative regulator of the IFN-β pathway. This occurs via the degradation of the MDA5-mediated cytoplasmic double-stranded RNA (dsRNA) antiviral sensing RIG-I-like receptor (RLR) pathway. We show that structural protein VP2 of EMCV interacts with MDA5, MAVS, and TBK1 through its C terminus. In addition, we found that EMCV VP2 could significantly degrade RLRs by the proteasomal and lysosomal pathways. For the first time, EMCV VP2 was shown to play an important role in EMCV evasion of the type I IFN signaling pathway. This study expands our understanding that EMCV utilizes its capsid protein VP2 to evade the host antiviral response.IMPORTANCE Encephalomyocarditis virus is an important pathogen that can cause encephalitis, myocarditis, neurological diseases, and reproductive disorders. It also causes huge economic losses for the swine industry worldwide. Innate immunity plays an important role in defending the host from pathogen infection. Understanding pathogen microorganisms evading the host immune system is of great importance. Currently, whether EMCV evades cytosolic RNA sensing and signaling is still poorly understood. In the present study, we found that viral protein VP2 antagonized the RLR signaling pathway by degrading MDA5, MAVS, and TBK1 protein expression to facilitate viral replication in HEK293 cells. The findings in this study identify a new mechanism for EMCV evading the host's innate immune response, which provide new insights into the virus-host interaction and help develop new antiviral approaches against EMCV.

Encephalomyocarditis virus infection in a splenectomised calf

BACKGROUND

Encephalomyocarditis (EMC) caused by EMC virus (EMCV) was diagnosed in a 5-month-old splenectomised calf, which died suddenly on an experimental farm that had a high infestation of rodents.

RESULTS

At postmortem examination, the lungs were dark purple and diffusely congested. On histological examination, the calf had severe necrotising myocarditis. EMCV was isolated from the heart. The polyprotein gene of the EMCV isolate was amplified by PCR and had 85-91% identity with published EMCV sequences, including 89% identity with isolates from Queensland. On phylogenetic analysis, the polyprotein gene had highest sequence identity with South Korean EMCV strain, CBNU.

CONCLUSION

This is the first report of naturally occurring EMC in cattle in Australia and the first report of naturally occurring bovine EMC from which EMCV has been isolated.

A novel vaccine combined with an alum adjuvant for porcine encephalomyocarditis virus (EMCV)-induced reproductive failure in pregnant sows

To evaluate a novel vaccine for porcine encephalomyocarditis virus (EMCV), which causes reproductive failure in pregnant sows, virus like particles (VLPs) were generated and immunized twice in 2 week intervals before sow mating. Sows were divided into 4 groups (n=4, per group). Group 1 was immunized with the alum adjuvant alone, Group 2 with VLPs alone, Group 3 with VLPs mixed alum adjuvant, and Group 4 with a commercial killed vaccine. In Group 2, seroconversion was observed at very low levels, while in Group 3, neutralizing antibodies were maintained at a high level until 30 days after farrowing. Similar levels neutralizing antibodies were observed in Group 4. The gestation period of the pregnant sows was on average 115 days, and no injection site reaction or side effects were observed. The mean temperature of the sows after immunization increased temporarily to 38.7-39.1 °C for 1 day. The numbers and weights of surviving piglets were similar among the groups. These data describe a novel EMCV vaccine composed of VLPs mixed with an alum adjuvant that is safe to use during sow gestation and induces and maintains high levels of seroconversion. This vaccine could thus be a candidate for protecting against EMCV induced reproductive failure in pig farms.

Immunogenicity and safety of virus-like particle of the porcine encephalomyocarditis virus in pig

Background

In this study, porcine encephalomyocarditis virus (EMCV) virus-like particles (VLPs) were generated using a baculovirus expression system and were tested for immunogenicity and protective efficacy in vivo.

Results

VLPs were successfully generated from Sf9 cells infected with recombinant baculovirus and were confirmed to be approximately 30-40 nm by transmission electron microscopy (TEM). Immunization of mice with 0.5 μg crude protein containing the VLPs resulted in significant protection from EMCV infection (90%). In swine, increased neutralizing antibody titers were observed following twice immunization with 2.0 μg crude protein containing VLPs. In addition, high levels of neutralizing antibodies (from 64 to 512 fold) were maintained during a test period following the second immunization. No severe injection site reactions were observed after immunization and all swine were healthy during the immunization period

Conclusion

Recombinant EMCV VLPs could represent a new vaccine candidate to protect against EMCV infection in pig farms.

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.

Immune responses and expression of the virus-like particle antigen of the porcine encephalomyocarditis virus

Virus-like particles (VLPs) are particles that consist of viral capsid proteins and are structurally similar to authentic virus. To express VLPs of the porcine encephalomyocarditis virus (EMCV) and investigate their efficacy and immuno response in vivo, a plasmid (P12A3C-pCI) containing the P12A and 3C genes of the EMCV-K3 viral strain was constructed. The VLPs of EMCV-K3 were successfully assembled in 293FT cells on 3 days after transfection with P12A3C-pCI and were identified as particles of about 30-40 nm using transmission electron microscopy (TEM). In an in vivo experiment, the murine cytokines induced by VLPs of naked DNA vaccine showed that the Th1 indicators IL-2, TNF-alpha and GM-CSF, and the Th2 indicators IL-4 and IL-10 were increased. The immunization of mice with the P12A3C-pCI plasmid induced high levels of neutralizing antibody from 128- to 256-fold and led to a significant protection ratio (90%) after challenge with EMCV-K3 (wild-type strain). These VLPs may represent a novel vaccine strategy for the control of EMCV infection on pig farms.

Mass mortality of adult male subantarctic fur seals: are alien mice the culprits?

BACKGROUND

Mass mortalities of marine mammals due to infectious agents are increasingly reported. However, in contrast to previous die-offs, which were indiscriminate with respect to sex and age, here we report a land-based mass mortality of Subantarctic fur seals with apparent exclusivity to adult males. An infectious agent with a male-predilection is the most plausible explanation for this die-off. Although pathogens with gender-biased transmission and pathologies are unusual, rodents are known sources of male-biased infectious agents and the invasive Mus musculus house mouse, occurs in seal rookeries.

METHODOLOGY/ PRINCIPAL FINDINGS

Molecular screening for male-biased pathogens in this potential rodent reservoir host revealed the absence of Cardiovirus and Leptospirosis genomes in heart and kidney samples, respectively, but identified a novel Streptococcus species with 30% prevalence in mouse kidneys.

CONCLUSIONS/ SIGNIFICANCE

Inter-species transmission through environmental contamination with this novel bacterium, whose congenerics display male-bias and have links to infirmity in seals and terrestrial mammals (including humans), highlights the need to further evaluate disease risks posed by alien invasive mice to native species, on this and other islands.

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.

Specific small interfering RNAs-mediated inhibition of replication of porcine encephalomyocarditis virus in BHK-21 cells

Encephalomyocarditis virus (EMCV) is recognized as a pathogen inducing acute myocarditis and sudden death in preweaned piglets and severe reproductive failure in sows. In this study, eight specific small interfering RNA (siRNA) duplexes targeting different genomic regions of EMCV BJC3 were designed and their ability to inhibit virus replication in BHK-21 cells was investigated. The results showed that BHK-21 cells transfected with siRNA duplexes to 2C gene (JH-4,666, BJC-1,739), 2B gene (BJC-807), 3C gene (BJC-2,363) and 3D gene (BJC-3269) were specifically resistant to EMCV infection when exposed to 500 times the 50% cell culture infective dose (CCID(50)) of EMCV. The levels of the 3D gene in the transfected cells were obviously decreased. IFA and Western blotting analysis confirmed that the expression of VP1 protein in cell culture transfected with the siRNAs was apparently reduced. Of the five siRNAs, JH-4,666, BJC-2,363 and BJC-3,269 were the most effective. Combination of the siRNA duplexes enhanced the inhibition of EMCV replication. Our data indicated that specific siRNAs are able to inhibit the replication of porcine encephalomyocarditis virus in BHK-21 cells, suggesting that RNAi might provide a new approach to prevent EMCV 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.

Serologic responses of Barbary sheep (Ammotragus lervia), Indian antelope (Antilope cervicapra), wallaroos (Macropus robustus), and chimpanzees (Pan troglodytes) to an inactivated encephalomyocarditis virus vaccine

Encephalomyocarditis virus (EMCV) is a picornavirus with a worldwide distribution, capable of infecting a wide range of species. Episodes of EMCV-associated mortality have been reported in zoos and national parks around the world, including sporadic cases at Taronga Zoo, Sydney. An inactivated EMCV vaccine was evaluated by inoculating Barbary sheep (Ammotragus lervia), Indian antelope (Antilope cervicapra), Eastern wallaroos (Macropus robustus), and chimpanzees (Pan troglodytes). A proportion of the vaccinated ungulates were administered a second vaccination 4 wk after the initial dose. Neutralizing antibody titers were monitored for a period of 12 mo. One month after vaccination, all vaccinated groups had developed significant antibody titers that persisted for at least 6 mo. Animals receiving two doses of vaccine had higher titers 3, 6, and 12 mo after the initial vaccination compared with animals receiving a single vaccine dose.

Innovative drug treatments for viral and autoimmune myocarditis

Myocarditis is a common cause of cardiomyopathy and is thought to account for 25% of all cases in humans. Unfortunately, the disease is difficult to detect clinically before a myopathic process ensues. Management of myocarditis-induced heart failure includes the standard regimen of diuretics, digoxin, angiotensin-converting enzyme inhibitors, angiotensin-II receptor blockers, and beta-adrenergic blockers. The management of myocarditis itself is dependent on the etiology of the illness. Treatments that are currently under investigation include immunosuppressants, nonsteroidal antiinflammatory agents, immunoglobulins, immunomodulation, antiadrenergics, calcium-channel blockers, angiotensin-converting enzyme inhibitors, nitric oxide inhibitors (e.g., aminoguanidine), and antivirals. Despite advances in treatment, more work needs to be done in the early detection of myocarditis. Additionally, better means need to be established for distinguishing between viral and noninfectious autoimmune forms of the disease, so that appropriate treatment can be instituted.

Pharmacokinetics and effects of succinylcholine in African elephant (Loxodonta africana) and impala (Aepyceros melampus)

The phenomenon of slow onset of succinylcholine (Sch) effect in elephants was investigated by analyzing blood concentrations of Sch and its metabolite choline in elephant and impala. To assess whether the slow onset phenomenon is related to the pharmacokinetics of Sch following i.m. administration, we analyzed the time course of plasma concentrations of intact drug and its metabolite and determined its pharmacological effects. Blood samples were obtained from anaesthetized elephant (n=6) and impala (n=7) following i.m. administration of a lethal dose of Sch. Time from Sch injection to onset of apnoea and to death was significantly longer for elephant than impala (mean+/-S.D. apnoea 4.4+/-1.5 and 2.3+/-0.9 min, respectively; death 32.6+/-7.3 and 6.2+/-3.4 min, respectively). The C(max) was not different between elephants and impala (20.3+/-7.9 vs. 14.4+/-6.8 nmol ml-1, respectively) but the t(max) was significantly longer for elephants (23.0+/-7.6 vs. 3.7+/-2.2 min). Analysis of the plasma Sch and choline concentrations over time revealed that the relative amount of Sch entering the circulation within the first 30 s after i.m. injection is greater for impala than elephant. No greater rate in the plasma hydrolysis of Sch in elephant compared to impala was apparent.