Encephalomyocarditis Virus in Pigs
Encephalomyocarditis virus (EMCV) has been
recognized as a swine pathogen responsible for sporadic
outbreaks for the last thirty years. It is classified in
the genus Cardiovirus in the family Picornaviridae.
The EMCV group is generally regarded as a rodent virus with
the principle vectors being rats and mice. The group can
naturally infect a wide range of vertebrate species, including
swine, which is the most susceptible of the domesticated
animals. To date there is no clear evidence to support
the role of EMCV as a pathogen in livestock other than swine.
The traditional manifestation of the disease
in swine is characterized by acute onset of disease with
sudden deaths due to myocardial failure in pre-weaning pigs.
Anorexia, listlessness, trembling, staggering, paralysis,
or dyspnea may also be observed. Younger pigs are usually
more susceptible with mortality reaching up to 100% in the
unweaned animals. Post-weaning pigs generally develop subclinical
infections. EMCV has been recovered from stillborn and
mummified fetuses demonstrating that transplacental infection
may occur. Infected pregnant sows may have near-term abortions
and low farrowing rates. Infertility problems seen in these
animals are attributed to fetal mummifications after intrauterine
Oral transmission through either rodent feces
or carcasses appears to be the most likely route of transmission.
Virus strain, viral dose, history and susceptibility of
the individual animal all appear to affect the course of
It is important when making a diagnosis to
differentiate EMCV from the other reproductive diseases.
History can be an important component to the diagnosis of
EMCV especially when it is one of reproductive failure with
high preweaning mortality. This can be seen in sows of
any parity, which can be used to distinguish from porcine
parvovirus, which is primarily manifested in gilt litters.
Dyspnea, due to heart failure, seen grossly as white necrotic
lesions in the heart, is characteristic of EMCV but should
be differentiated from Selenium/Vit. E deficiency. *
Virus isolation and identification is considered necessary
for a definitive diagnosis. Since there is no transmission
of maternal immunoglobulins across the placenta in pigs,
detection of antibody specific to EMCV from stillborn or
large mummified fetuses is significant for fetal infection.
EMCV has no treatment, however, there is an
apparently effective inactivated vaccine available in the
Energy should, therefore, be utilized to control the rodent
population on the farms as well as minimize stress among
the affected pigs. Disinfection can be accomplished using
mercuric chloride or iodine-based solutions when necessary.
The virus seems to replicate in the intestine and cause
a viremia within 2 days of infection. The highest titers
are obtained from the head, but spleen, mesenteric lymph
nodes, liver, pancreas and kidney also contain virus.
*Other gross lesions may include hydropericardium, hydrothorax,
pulmonary edema and ascitis. The most common microscopic
lesions are necroses of myocardial fibers with mononuclear
cell infiltration. Perivascular accumulation of mononuclear
cells can also be observed in the meninges and brain.
-by Jason K. Huff, Class of 2000
-edited by Marlon Rebelatto, DVM,