Diagnostic methods in infectious respiratory disease

For laboratory diagnosis of respiratory disease it is of overwhelming importance that the specimens taken are adequate, taken from the correct site and at the correct time. The lower regions of the respiratory tract are particularly difficult to sample but are more likely to yield the causative agent of a pneumonia. Infections involving the upper respiratory tract are much easier to sample and appropriate aspiration apparatus can be used. Consideration must be given to the timing of sample collection in relation to the life cycle of the causative micro-organism. Sampling of several animals is recommended. Diagnosis may be achieved by isolation in culture of the causative agent or the demonstration of the agent by indirect methods such as electron microscopy and ELISA. Clinical biochemical tests may reflect systemic metabolic changes induced by microbial infections and give an indication of the severity of the disease and its prognosis. Pulmonary function tests have limited application in animals and are only likely to be used under experimental conditions and in horses and small animals.