The main reservoir host for the EMC virus is the rat although mice may also spread it. It infects and causes disease in a wide range of vertebrate animals but pigs appear to be the most susceptible of farm animal species. The virus is world-wide but differs in pathogenicity and virulence in different countries and regions. In most countries of Europe, particularly those in the EU, it tends to be relatively mild or non-pathogenic and disease in pigs is rarely diagnosed.

In Australia the strains appear to be much more virulent for pigs than those in New Zealand. Virulent strains in Florida, the Caribbean and probably Central America damage the heart and cause death whereas those in the Mid West of the US tend to cause reproductive problems.

Clinical disease in pigs tends to occur when rat numbers increase to plague levels. Pigs can be infected from rats or from rat-contaminated feed or water. It does not seem to spread very readily between pigs.

In affected herds there are usually no clinical signs in weaned and growing pigs.

Symptoms

Sows

In gilts and sows first signs are often :

• A few abortions near the end of pregnancy.

Then over a period of about 3 months

• The numbers of mummified foetuses and stillbirths increase and pre-weaning mortality rises.
• The farrowing rate worsens.
• Affected females may show signs of fever and lack of appetite.
• Embryo death
• In affected herds there are usually no clinical signs in weaned and growing pigs.

Piglets,

• Poor viable.
• Usually none.

Weaners & Growers

• N/A

Causes / Contributing factors

• Pigs can be infected from rats or from rat-contaminated feed, water or bedding.
• Disease does not seem to spread very readily between pigs.
• Incoming breeding stock with pathogenic strain.

Diagnosis

To make a definitive diagnosis the virus has to be isolated and identified or rising antibodies demonstrated in blood samples taken two weeks apart.

EMC could be confused with AD, parvovirus infection and PRRS although there are distinguishing signs between these four. EMCV would be the last on the list of diagnostic priorities in Europe but to a lesser extent in the Mid West USA. Abortion or illness in sows or piglets due to PPV is uncommon and mummified pigs can be examined for the evidence of this infection.