ENCEPHALOMYOCARDITTS VIRUS INFECTION OF PIGS 1. An Outbreak in New South Wales

Abstract

Substantial pig mortalities due to heart disease caused by EMC virus infection are described. The majority occurred in 1970 in conjunction with a rodent plague, but retrospective diagnosis of occasional similar mortalities in previous years was possible. Mortality rates in pigs aged 3 to 16 weeks ranged from a few percent to over 50% and the rate was generally highest in younger animals. It is likely that a considerable proportion of cases was sub-clinical. Focal or diffuse pale areas occurred in the myocardium, the wall of the conus arteriosus being most severely affected. In a few animals, resolving lesions were present. Encephalomyocarditis virus was consistently recovered from pigs with acute heart lesions, but not from those in which myocardial fibrosis had commenced. The virus was demonstrated in rodents, although the dependence of pig disease on rodent-derived virus could not be established. Because of similarities between EMC and FMD myocarditides in pigs, specific diagnosis by virus isolation and identification should be obtained whenever possible.

Pathogenesis of encephalomyocarditis experimental infection in young piglets: a potential animal model to study viral myocarditis

“…In swine, historical knowledge about the pathogenicity of EMCV indicates the heart as the main target organ [1,2,4,21,22]. In Table I.…”

“…Isolates that have caused myocarditis in pigs have been associated with rodent outbreaks [2,19,30]. In wild rodents, the natural hosts, the virus usually persists without causing disease [32], whereas infection in laboratory rodents commonly [30] produces fatal encephalitis or myocarditis [7,9,23,27,33,38].…”

“…In swine, the reported natural infections with EMCV have different epidemiological characteristics, probably depending on different EMCV strains which act with different pathogenicity [1,6]. EMCV has been recognised as a cause of fatal myocarditis in young piglets or reproductive failure in sows [1,2,6,17,19,21,26,30]. In Europe, EMCV was first isolated in an outbreak of fatal myocarditis in Italy in 1986 [16].…”

“…In Belgium, the virus has been frequently isolated in association with reproductive failure since 1991 [17], EMCV was isolated in Belgium in 1995 from an outbreak of fatal myocarditis in fattening pigs [19]. In dead pigs the dominant lesion could show focal to multifocal mononuclear myocarditis with myocardial necrosis [1,2,21]. The present paper was aimed at providing additional information of the pathogenesis of a Belgian isolate of EMCV in different organs in experimentally infected piglets.…”

Transmission and pathogenicity of encephalomyocarditis virus (EMCV) among rats

“…The high seroprevalence levels found in the field and the observed clinical infections in separated pens and compartments of affected pig houses might therefore point to an additional spreading mechanism, for example via rodents. Although it is known that rats can be infected with the EMC virus [2], only little is known about the spread of the virus within the rat population. More insight into the transmission of EMCV among rats might enlighten their role as a possible transmitter or a potential reservoir for the EMC virus and stress the need for an effective rodent control programme at the farm level.…”