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Although the incubation period for classical swine fever is generally less than ten days, in the field it may take up to four weeks for clinical signs to become apparent in a population. Disease severity varies with virulence, immune status and the age of the animal: this means that although acute, chronic and congenital forms of the disease can be appreciated, there is no "classic" disease presentation.
 
Although the incubation period for classical swine fever is generally less than ten days, in the field it may take up to four weeks for clinical signs to become apparent in a population. Disease severity varies with virulence, immune status and the age of the animal: this means that although acute, chronic and congenital forms of the disease can be appreciated, there is no "classic" disease presentation.
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In the acute form, animals are almost always pyrexic. In piglets under 12 weeks old the fever may exceed 40°, but in adults
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In the acute form, animals are almost always pyrexic. In piglets under 12 weeks old the fever may exceed 40°, but in adults temperatures may be no higher than 39.5°. Lethargy, conjunctivitis, lymphomegaly may be seen, as well as respiratory signs and diarrhoea. Neurological signs such as gait abnormalities, incoordination and convulsions are also common. The most telling sign of classical swine fever is haemorrhage of the skin. These arise in the second or third week post-infection on the ear, tail, abdomen and medial aspect of the limbs and persist until death.
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Piglets up to 12 weeks of age most often display
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the acute form. A constant finding is pyrexia, usually
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higher than 40 �C, but in adults the temperature
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may not exceed 39.5 �C. Initial signs are anorexia,
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lethargy, conjunctivitis, enlarged and discoloured
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lymph nodes, respiratory signs and constipation
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followed by diarrhoea. Neurological signs are frequently
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seen, such as a staggering gait with weakness
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of hind legs, incoordination of movement, and
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convulsions (Fig. 1). The typical haemorrhages of
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the skin are usually observed on the ear, tail, abdomen
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and the inner side of the limbs during the
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second and third week after infection until death.
   
The virus is shed from the infected animal by saliva,
 
The virus is shed from the infected animal by saliva,
 
urine and faeces (Depner et al., 1994; Laevens et al.,
 
urine and faeces (Depner et al., 1994; Laevens et al.,
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