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