Exotic Diseases

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Species Infected

affects sheep

has been reported in goats

Clinical Signs

• incubation more than 3 years
• loss of body condition
• affected animals will lag, not because of motor incoordination, but because of respiratory distress
• after exercise marked increase in respiratory rate to 120 per minute
• head may jerk rhythmically with respiration
• may be slight nasal discharge and coughing
• affected animals will spend majority of time laying down
• if secondary infection does not supervene, condition will last 3-8 months
• pregnant ewes may abort or deliver weak lambs
• morbidity can be up to 20% with 100% mortality of clinical cases

Lesions

• confined to thorax
• lungs fail to collapse
• enlarged 2-3 times normal and may be moulded to shape of rib cage
• colour greyish-brown to greyish-blue
• diaphragmatic lobes more affected
• but no sharp demarcation of lesions
• consistency of firm sponge rubber
• there may be a few adhesions
• cut surface dry/homogenous in appearance
• lymph nodes always greatly enlarged
• histopathology: chronic diffuse interstitial pneumonia

Aetiology

• Lentivirus (Retroviridae)
• same virus as visna
• why it causes 2 distinct diseases is not certain
• may be both host susceptibility and virus strain dependent

Pathogenesis

• maedi and not visna is the most frequent manifestation of infection but uncertain why
• most infection appears to occur soon after birth
• considered that host mediated immune mechanisms may be involved in the development of a progressive pneumonia

Epidemiology

• as for visna

Differential Diagnoses

     1.  pulmonary adenomatosis
     2.  verminous pneumonia
     3.  caseous lymphadenitis with pulmonary involvement