Background and history

These are gut-borne viruses, host specific to the pig, that are described under the name SMEDI viruses which stands for stillbirth, mummification, embryonic death and infertility. The term is now also commonly used for parvovirus infection. Although these groups of viruses are distinct from that of parvovirus, they are often all grouped together clinically because the clinical signs are similar. The enteroviruses are subdivided into serotypes of which at least 11 are known. Four of these, serotypes 1, 3, 6 and 8, have been implicated in reproductive problems in pigs. Serotype 1 is the teschen /talfan virus which can also cause paralysis in pigs. Usually, each pig herd has an array of different serotypes which circulate in weaned and young growing pigs sub-clinically. The pigs are protected by circulatory antibodies derived from their dam's colostrum. By the time they reach breeding age they are solidly immune.

Reproductive problems only occur when a new serotype, to which the gilts are not immune, enters the herd and multiplies in the breeding females. This probably does not happen very often.

It is interesting to note that since the introduction of parvovirus vaccine and the excellent results achieved, the effects from SMEDI viruses would appear to be almost non existent, suggesting that this group of viruses are not important as a cause of reproductive failure.

Similar diseases

SMEDI can be confused with PPV and PRRS infection and occasionally with AD and leptospirosis.

Clinical signs

Natural infection of enteroviruses takes place by mouth through the ingestion of infected faeces. They multiply in the small and large intestines and in the absence of circulating antibodies escape from the intestine into the blood streams to the uterus. They cross the placenta, to produce the typical symptoms of embryo mortality, mummification and stillbirths. In some cases infertility associated with absorption of embryos also occur. If reproductive failure results there will be increases in embryo mortality, foetal deaths and mummified and stillborn piglets. Infection and disease only occur in non-immune sero-negative animals.

Diagnosis

This is carried out by serology and virus isolation.

Causes

A group of enteroviruses, subdivided into serotypes of which at least 11 are known. Four of these, serotypes 1, 3, 6 and 8, have been implicated in reproductive problems in pigs. Serotype 1 is the teschen /talfan virus which can also cause paralysis in pigs.

Prevention

• Expose breeding females and boars to faeces from young growing pigs 8-14 weeks of age to immunise them (feedback). This is best carried out by introducing gilts at 90kg to faeces from pigs 15-50kg weight, twice weekly for 6 weeks prior to mating.
• The practice of feeding placenta should be avoided, because it is not a good source of infection and it is a method of spreading leptospirosis, PRRS and other potentially infectious agents.
• Vaccines could be made but are not indicated.

Treatment

• There is no treatment but if a herd experiences problems with enteroviruses in incoming gilts, management practices should ensure that gilts are exposed to infection at least six weeks before breeding. See acclimatisation chapter 5.