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

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

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

Isolation and molecular characterization of a second serotype of the encephalomyocarditis virus

Encephalomyocarditis virus (EMCV) and Theilovirus are the two species of the Cardiovirus genus. Whereas theiloviruses comprise several sero-/genotypes, all known EMCV isolates are serologically very similar and are thought to belong to one serotype, named EMCV-1. Here, a novel EMCV type is described. Strain RD 1338 (D28/05) was isolated from a wood mouse (Apodemus sylvaticus) in Germany and can be distinguished from EMCV-1 by serological and molecular means. Failure of EMCV-1 specific hyperimmune sera to neutralize RD 1338 suggests a distinct serotype. The viral genome was de novo sequenced using next-generation Illumina/Solexa technologies. Considerable differences of the BC-loop/loop I/loop II sequences of VP1, the VP2 puff and the VP3 knob provide a structural basis for deviant serological properties. Sequence alignments reveal amino acid identities of 75 percent for the P1 region and 84 percent for the P2 and P3 regions when comparing RD 1338 to EMCV-1 strains and some 60 percent and less than 50 percent amino acid identities, respectively, for comparisons with theilovirus strains. Phylogenetic analyses of the P1, 2C and 3CD gene regions support the establishment of an EMCV-2 serotype. In contrast to the theilovirus sero-/genotypes that show a narrow host range, EMCV-1 infects a wide variety of hosts. The host range of EMCV-2 remains to be determined.

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.

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

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