Correlation between the presence of enzootic pneumonia lesions and detection of Mycoplasma hyopneumoniae in bronchial swabs by PCR.

In many diagnostic laboratories the diagnosis of mycoplasmal pneumonia in pigs is based on clinical signs and the presence of gross and histopathological lesions. The objective of this study was to evaluate the nested-PCR technique as an adjunct to the histopathological diagnosis of Mycoplasma hyopneumoniae infection. Respiratory disease of 184 swine cases submitted to the Minnesota Veterinary Diagnostic Laboratory between 1 January and 30 June 1998 were used. Bronchial swabs were collected and the nested-PCR performed. Lung samples were graded PCR positive or negative. Histopathological lesions were scored 0-4, depending on the mycoplasma-like characteristics of the lesions, with category 4 demonstrating strong evidence of mycoplasma infection.Nested-PCR correlated well with histopathological lesions characteristic of M. hyopneumoniae in categories 3 and 4 and approximately half of the histopathological categories 1 and 2 were nested-PCR positive. The results demonstrate that the nested-PCR is a valuable adjunct in the diagnosis of M. hyopneumoniae infection when non-diagnostic microscopic lesions of mycoplasmosis are found.