Encephalomyocarditis virus disease of pigs associated with a plague of rodents

Abstract

An epizootic of encephalomyocarditis virus (EMCV) disease in pigs in the central west of New South Wales in association with a plague of mice (Mus musculus) in 1984 is described. The disease was confirmed in 47 outbreaks in 37 piggeries and 1152 pigs died, representing an overall death rate of 17.4% in pigs considered at risk. The disease was diagnosed in both intensively housed pigs and pigs farmed outdoors, with mortality rates higher in piggeries with less than 50 sows. The age at which pigs died ranged from 4 days to 24 weeks with higher death rates in younger pigs. Serological testing of pigs slaughtered at Blayney abattoir indicated EMCV infection to be more widespread than the disease reported. Mice were present in all piggeries reporting the disease while rats were present in 66% of the outbreaks. The role of rodents as natural reservoirs of EMCV and the possibility of variations in pathogenicity amongst strains of the virus are discussed.

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

“…It is ubiquitous in nature and has been isolated from both animals (insects, birds, mammals) and humans [35,40]. Several studies indicate that EMCV can cause interspecies infections, making it a potential zoonotic agent [5,13,16,28,30]. However, most of the evidence of human infection has been indirect, detected from the presence of antibodies.…”

“…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].…”

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

“…Neutralising antibodies can be detected as early as 5 days postinoculation in experimentally infected pigs [1], whereas the virus can be isolated from blood and excreta already one day after inoculation [3,7,17]. EMCV-transmission has been described from rodents to a wide variety of other species, including humans [1,16,22], while a recent study indicated that rats easily spread the virus among each other [24]. Although EMCV-transmission from rodents to pigs is considered important, also the impact of horizontal and vertical pig-to-pig transmission needs to be known/quantified to understand their contribution to the spread of the disease on a pig farm [7,17].…”

Transmission and pathogenicity of encephalomyocarditis virus (EMCV) among rats

“…At first, pigs might get infected by the ingestion of substances (e.g. faeces or carcasses) of infected rodents [1,20,23]. The second route is horizontal pig-to-pig transmission during the short period of viraemia [4,17] or after reactivation of EMCV persistence [5].…”