Exotic Diseases

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Species Infected

affects sheep, cattle, goats, other ruminants, rodents, man

Clinical Signs

• dependent on species and age affected - the younger the more severe

Sheep, Goats

• young
• peracute
• sudden death
• acute
• incubation 2-4 days
• fever
• vomition, dysentery
• muscular pain, staggering gait
• mucopurulent nasal discharge
• petechiae on visible mucous membranes
• death 24-48 hours
• 90-100% mortality
• adults
• transient fever
• inappetence
• muscle weakness
• icterus
• abortion
• mortality 20-30%
• some from septic metritis

Cattle

• similar signs but lower mortality and abortion rates

Man

• incubation 4-6 days
• severe influenza-like disease
• complications
• encephalitis
• retinitis and detachment
• hepatic necrosis
• mortalities do occur up to 0.5%

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Lesions


• necrosis of liver is characteristic
• multiple haemorrhages in most tissues and organs
• tarry appearance of intestinal contents especially caecum
• thickened, oedematous gall bladder

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Aetiology

• Phlebovirus (Bunyaviridae)
• no antigenic variants
• vectors - large numbers of mosquito species

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Pathogenesis

• high viraemia develops
• hepatic multiplication induces severe necrosis and hepatic insufficiency

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Epidemiology

• periodic epidemics occur at 5-20 year intervals
• these initiate from endemic foci when seasons of unusually heavy rainfall occurs and where irrigation channels and swamps provide ample mosquito breeding areas
• wind blown vectors can carry disease long distances
• of importance also is the presence of susceptible livestock
• mechanism of interepidemic infection poorly understood
• endemic foci do occur in Kenya, Zimbabwe and South Africa, but whether wild ruminants instead of domesticated animals are primarily responsible is unknown
• man - infection primarily by handling infected materials and animals, not via vector
• high viraemia in man and could be a source of introduction into new country
• non vector borne transmission between livestock possible but not significant

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Differential Diagnoses

     1.  enterotoxaemia
     2.  other causes of abortion
     3.  hepatotoxins
     4.  leptospirosis
     5.  bluetongue
     6.  Wesselsbron disease (Flaviviridae)