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

The Reproduction Number of Swine Viral Respiratory Diseases: A Systematic Review

Diseases in the swine industry can cause significant economic and health impacts. This review examines R0 estimates for respiratory diseases in pigs, assessing variations and comparing transmission risks within and between farms. A literature search of three databases aggregated peer-reviewed research articles on swine viral respiratory diseases' R0 values. The study focused on seven diseases: Aujeszky's disease (AD), Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), Circovirus, Influenza A (IA), Encephalomyocarditis Virus (EV), Classical Swine Fever (CSF), and African Swine Fever (ASF). R0 values were estimated for transmission within and between herds/farms using various methods, from complex mathematical models to simple calculations. Data primarily came from disease surveillance and laboratory experiments. The median R0 for within-herd and between-herd transmission was 10 and 3.31 for AD, 2.78 and 1.14 for PRRSV, 5.9 and 0.89 for Circovirus, 1.75 and 1.6 for CSF, and 3.94 and 3.15 for ASF. For IA and EV, only within-herd R0 values were estimated at 8.65 and 1.3, respectively. Diseases with high R0 values highlight the need for prompt detection and response to outbreaks. Continuous monitoring and evaluation of pathogen transmissibility are crucial for enhancing disease surveillance and reducing the impact of livestock diseases.

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.

Identification of the Cell-Surface Protease ADAM9 as an Entry Factor for Encephalomyocarditis Virus

EMCV is an animal pathogen that causes acute viral infections, usually myocarditis or encephalitis. It is thought to circulate mainly among rodents, from which it is occasionally transmitted to other animal species, including humans. EMCV causes fatal outbreaks of myocarditis and encephalitis in pig farms and zoos, making it an important veterinary pathogen. Although EMCV has been widely used as a model to study mechanisms of viral disease in mice, little is known about its entry mechanism. Here, we employ a haploid genetic screen for EMCV host factors and identify an essential role for ADAM9 in EMCV entry.

Encephalomyocarditis virus (EMCV) is an animal pathogen and an important model organism, whose receptor requirements are poorly understood. Here, we employed a genome-wide haploid genetic screen to identify novel EMCV host factors. In addition to the previously described picornavirus receptors sialic acid and glycosaminoglycans, this screen unveiled important new host factors for EMCV. These factors include components of the fibroblast growth factor (FGF) signaling pathway, such as the potential receptors FGFR1 and ADAM9, a cell-surface metalloproteinase. By employing various knockout cells, we confirmed the importance of the identified host factors for EMCV infection. The largest reduction in infection efficiency was observed in cells lacking ADAM9. Pharmacological inhibition of the metalloproteinase activity of ADAM9 did not affect virus infection. Moreover, reconstitution of inactive ADAM9 in knockout cells restored susceptibility to EMCV, pointing to a proteinase-independent role of ADAM9 in mediating EMCV infection. Using neutralization assays with ADAM9-specific antiserum and soluble receptor proteins, we provided evidence for a role of ADAM9 in EMCV entry. Finally, binding assays showed that ADAM9 facilitates attachment of EMCV to the cell surface. Together, our findings reveal a role for ADAM9 as a novel receptor or cofactor for EMCV.

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.

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.

Detection and characterization of potentially zoonotic viruses in faeces of pigs at slaughter in Germany

Pigs can harbour a variety of viruses in their gastrointestinal tract. Some of them are closely related to human viruses and are therefore suspected to have a zoonotic potential. Only little is known about the presence of those viruses in pigs at slaughter. However, by contamination of meat with zoonotic viruses during the slaughtering process, food-borne transmission to humans may be possible. Here we analyzed 120 faecal samples of pigs at slaughter from 3 different geographical regions of Germany for the presence of astrovirus (AstV), encephalomyocarditis virus (EMCV), hepatitis E virus (HEV), norovirus genogroup II (NoV GII) and group A rotavirus (GARV). Using real-time RT-PCR, the most frequently detected virus was AstV, which was present in 20.8% of the samples, followed by NoV GII with a detection rate of 14.2%. EMCV, HEV and GARV were found only occasionally with detection rates of 4.2%, 2.5% and 0.8%, respectively. Analyses of partial genome sequences of the viruses indicated that the detected AstV and NoV GII mainly represented typical pig virus strains, which have not been detected in humans so far. However, the GARV and HEV strains were more closely related to human strains. The results indicate that enteric viruses, some of them with zoonotic potential, are present in pig faeces at slaughter. Application of good hygiene practice is necessary to minimize the risk of introducing these viruses into the food and to prevent virus transmission to highly exposed persons such as slaughterers and veterinarians.

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.

Vaccination of influenza a virus decreases transmission rates in pigs

Limited information is available on the transmission and spread of influenza virus in pig populations with differing immune statuses. In this study we assessed differences in transmission patterns and quantified the spread of a triple reassortant H1N1 influenza virus in naïve and vaccinated pig populations by estimating the reproduction ratio (R) of infection (i.e. the number of secondary infections caused by an infectious individual) using a deterministic Susceptible-Infectious-Recovered (SIR) model, fitted on experimental data. One hundred and ten pigs were distributed in ten isolated rooms as follows: (i) non-vaccinated (NV), (ii) vaccinated with a heterologous vaccine (HE), and (iii) vaccinated with a homologous inactivated vaccine (HO). The study was run with multiple replicates and for each replicate, an infected non-vaccinated pig was placed with 10 contact pigs for two weeks and transmission of influenza evaluated daily by analyzing individual nasal swabs by RT-PCR. A statistically significant difference between R estimates was observed between vaccinated and non-vaccinated pigs (p < 0.05). A statistically significant reduction in transmission was observed in the vaccinated groups where R (95%CI) was 1 (0.39-2.09) and 0 for the HE and the HO groups respectively, compared to an R_o value of 10.66 (6.57-16.46) in NV pigs (p < 0.05). Transmission in the HE group was delayed and variable when compared to the NV group and transmission could not be detected in the HO group. Results from this study indicate that influenza vaccines can be used to decrease susceptibility to influenza infection and decrease influenza transmission.

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.