Exotic Diseases

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Species Infected

primarily a disease of cattle

some reports in buffalo, yaks, antelope, etc.

Clinical Signs

• incubation period 3-6 weeks
• range of signs including mild or inapparent disease
• acute disease
• high fever 40°C
• anorexia, drop in milk production
• depression
• may lag behind
• development of respiratory symptoms
• cough, laboured respiration
• mucoid nasal discharge
• on auscultation, sounds are related to pleurisy, pleural exudate and pneumonia
• respiratory symptoms to a lesser degree as above may manifest in inapparently affected animals following exercise
• chronic disease
• may appear normal
• when herded provokes a violent and prolonged cough
• poor condition, fail to fatten
• death can occur in up to 3 weeks
• morbidity 90%; mortality up to 50%

Lesions

• acute
• severe fibrinous pneumonia
• copious pleural exudate
• affected areas of lung swollen
• colour varies from deep pink to dark red; related to stages of "hepatisation"
• clear exudate from cut surface
• thickened interlobular septae; these coupled with varying colours of affected lobules gives rise to characteristic "marbled" appearance.
• pleura thickened, covered with fibrin
• blood vessel thromboses
• pulmonary necrosis can occur early
• duller in colour, become surrounded by a fibrous capsule and persist
• renal infarcts can occur
• chronic
• necrotic sequestered lesions retain much of the architecture of acute lesions
• may occasionally get liquefaction
• adhesions occur between parietal and visceral pleura

Aetiology

• Mycoplasma mycoides var mycoides
• sensitive to all environmental influences surviving only for a few hours

Pathogenesis

• infection is by inhalation from active or carrier cases
• a septicaemia develops with localisation in lungs and kidneys
• the essential element in the disease is thrombosis of pulmonary vessels, but the mechanism for this is unknown
• death is due ultimately to anoxia and toxaemia

Epidemiology

• as the organism is very susceptible to environmental influences the sole spread is by inhalation of infected aerosols
• some suggest that this is not only by inhalation of pulmonary aerosols but also by inhalation of infected urinary droplets
• yards, transport, paddocks, troughs do not transfer infection
• infection requires close animal contact such as occurs in housing, trucking, droving, watering holes etc.
• source of infection often provided by a recovered carrier animal in which a pulmonary sequestrum can act as a reservoir of infection for up to 3 years
• stress, intercurrent infection can lead to sequestrum breaking down
• this animal may become an active case
• strong immunity does occur after disease
• vaccination has been used successfully as part of disease control

Differential Diagnoses

     1.  other bacterial pneumonias, e.g. pasteurellosis
     2.  inhalation pneumonia
     3.  chronic fascioliasis
     4.  traumatic pericarditis
     5.  atypical interstitial pneumonia