Encephalomyocarditis

Infection caused by Encephalomyocarditis virus, found globally. Usually it is of no clinical importance, but there are some myocarditis cases with high mortality or reproductive problems.

Alternative names: EMC

The main host and reservoir of the encephalomyocarditis virus is the rat, although the mouse can also transmit it. It infects and causes disease in a wide variety of vertebrate animals. In North America, pigs appear to be the most susceptible of the production animals. The virus is found throughout the world but differs in virulence and pathogenicity depending on the country and region. In most European countries, mainly those of the European Union, it tends to be relatively mild or non-pathogenic and the disease is rarely diagnosed.

In Australia, strains appear to be much more virulent for pigs than those in New Zealand. Strains in Florida, the Caribbean and probably Central America affect the heart and cause death, while those same strains often cause reproductive problems in the Midwestern United States.

Sows
First symptoms:

Some abortions near the end of gestation.

• Increased number of mummies and stillborn piglets, as well as pre-weaning mortality.
• Lower farrowing rate.
• Affected sows may show symptoms such as fever and lack of appetite.
• Clinical signs are not usually observed on affected fattening farms.
• Embryonic death.

Nursing piglets

• Sudden death.
• Respiratory symptoms.
• Tremors.
• Lack of coordination or paralysis.
• Low viability.
• Usually no symptoms.

Nursery and fattening stage

•  Not seen.

• Pigs can be infected by rats, or feed and water contaminated by rats.
• The clinical disease usually occurs when the number of rats increases to infestation level.
• It does not seem to spread widely among pigs.
• Replacement gilts may be infected with pathogenic strains.

To make a definitive diagnosis the virus must be isolated and identified or an increase in blood antibodies must be demonstrated in two samples taken in 2 weeks apart. Encephalomyocarditis can be confused with Aujeszky, parvovirus, and PRRS virus, although there are symptoms that differentiate these four infections. Encephalomyocarditis virus would be the last on the list of diagnostic priorities in Europe. It is rare that parvovirus causes abortion or disease in sows or piglets; mummified piglets can be examined for evidence of this infection. 

• There is no treatment.
• Rat control.
• A possible vaccine (its efficacy is not very clear).