Exotic Diseases

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Species Infected

affects only pigs

Clinical Signs

• vary with strain of virus and between animals
• incubation period 2-6 days
• virulent virus
• all ages affected
• at beginning of outbreak only a few animals will appear affected
• lethargy and fever
• anorexia, weakness and staggering
• conjunctivitis develops with gumming of eyelids
• vomiting and diarrhoea
• reddening/purpling of skin of snout, ears, abdomen, medial aspect of legs
• death 5-20 days post-infection
• mortality up to 90%
• low virulent virus
• some recover
• period of illness longer, 30 days or more
• anorexia, depression
• failure to thrive
• variable mortality, 1-60%
• subclinical infection in sows in UK induces embryonic death, malformations, stillbirths
• if piglets survive may have tremors and transmit acute disease to older pigs

Lesions

• damage to endothelium leads to oedema and multiple haemorrhages
• lymph nodes oedema, haemorrhage peripheral region of nodes
• petechiae and ecchymoses of kidney, urinary bladder, stomach, intestinal mucosa and larynx
• splenic infarction
• pathognomonic infarction of colonic submucosal vessels causes button ulcers
• small necrotic circular lesions that are exacerbated by secondary bacterial infection
• discolouration of skin, secondary to endothelial damage
• bronchopneumonia, congestion and occasional infarction of myocardium

Aetiology

• Pestivirus (Flaviviridae)
• related to bovine viral diarrhoea virus
• survives for long periods under favourable conditions especially in pork and pork products
• strain variation from virulent to avirulent, with low virulence strains increasing in prevalence

Pathogenesis

• viral entry primarily by ingestion but can enter other mucous membranes or through abrasions and inhalation
• early replication in tonsils followed by multiplication in cervical lymphoid tissue
• by 16 hr a viraemia develops and replication then occurs in spleen and other lymphoid and haematopoietic tissues
• invades parenchymatous organs 3-4 days
• many lesions are referable to endothelial damage and thrombosis of blood vessels
• death or recovery follows this phase

Epidemiology

• spread by direct contact between pigs or by contaminated feed, fomites or environment
• carrier sow giving birth to infected piglets does have important role in spread of disease
• entry into herd can be through contaminated pork in garbage, via infected pigs or by contaminated materials (e.g. trucks)

Differential Diagnoses

     1.  African swine fever - clinically cannot be readily differentiated from swine fever
     2.  pseudorabies
     3.  acute salmonellosis
     4.  erysipelas
     5.  pasteurellosis
     6.  infection by bovine viral diarrhoea virus
     7.  thrombocytopaenia purpura
     8.  warfarin poisoning
     9.  heavy metal poisoning