ANNEX

MANUAL OF DIAGNOSTIC PROCEDURES, SAMPLING METHODS AND CRITERIA FOR THE EVALUATION OF THE RESULTS OF LABORATORY TESTS FOR THE CONFIRMATION AND DIFFERENTIAL DIAGNOSIS OF SWINE VESICULAR DISEASE
CHAPTER IX

Clinical signs and features of swine vesicular disease
Swine vesicular disease is a contagious disease of pigs caused by an enterovirus of the picornaviridae family, which can be a sub-clinical, mild or severe vesicular condition depending on the strain of virus involved, the route and dose of infection, and the husbandry conditions under which the pigs are kept. Additional stress factors such as transport, mixing with other pigs and temperature extremes could also predispose to the development of clinical signs.
It is characterised by a mild fever and vesicles on the coronary band, the bulbs of the heel, skin of the limbs and less frequently the snout, lips, tongue and teats. The morbidity rate may be as high as 100 % but mortality is very low or nil.
Infection can develop in an inapparent or mild form showing only a transitory decline in the general appearance of pigs but leading to the development of virus neutralising antibodies in a few day .
Because of the subclinical or mild nature of the disease, it is often first suspected following serological tests for disease surveillance or export certification. Recent European outbreaks of swine vesicular disease have been characterised by less severe or no clinical signs, diagnosis frequently being dependent on serology.
However, clinical signs of swine vesicular disease are indistinguishable from those of foot-and-mouth disease. Any vesicular condition must be treated initially as suspected foot-and-mouth disease and differential diagnosis must be obtained as quickly as possible.
The incubation period of swine vesicular disease in individual pigs is usually between two and seven days, after which a transient fever of up to 41 °C may occur, but clinical signs may become evident in the holding after a longer period. Vesicles then develop on the coronary band, typically at the junction with the heel. These may affect the whole coronary band resulting in loss of the hoof. More rarely, vesicles may also appear on the snout, particularly on the dorsal surface, on the lips, tongue and teats, and shallow erosions may be seen on the knees. Affected pigs may be lame and off their feed for a few days.
Younger pigs are more severely affected, although mortality due to swine vesicular disease is very rare, in contrast with foot-and-mouth disease in young stock.
Nervous signs have been reported, but are unusual. Abortion is not a typical feature of swine vesicular disease. Cardiac failure due to multifocal myocarditis can be a feature of foot-and-mouth disease and encephalomyocarditis, especially in young piglets, but does not occur in swine vesicular disease.
Recovery is usually complete in two to three weeks, with the only evidence of infection being a dark, horizontal line on the hoof where growth has been temporarily interrupted.
Affected pigs may excrete virus from the nose and mouth and in the faeces up to 48 hours before the onset of clinical signs. Most virus is produced in the first seven days after infection, and virus excretion from the nose and mouth normally stops within two weeks. Virus can be isolated from the faeces for up to 20 days after infection, although it has been reported present for up to three months. It can persist for a considerable period of time in the necrotic tissue associated with ruptured vesicles and in the faeces.
Specific IgM can be usually detected in the blood from two to three days post infection and disappear after about 30 to 50 days; specific IgG can be usually detected in the blood from 10 to 14 days post infection and last for some years. The Ig isotype can be determined by means of the ELISA described in Chapter VIII(B)(2).