Diagnosis of mycoplasmal pneumonia of swine: sequential study by direct immunofluorescence.

An improved direct fluorescent antibody test was evaluated for specificity and efficacy in diagnosing mycoplasmal pneumonia of swine. A sequential study was carried out in which pigs inoculated with a pneumonic lung suspension containing Mycoplasma hyopneumoniae strain 11 were euthanatized at postinoculation (PI) weeks 2 to 12. Fluorescent coating of M hyopneumoniae was detected primarily on bronchial and bronchiolar epithelial surfaces of lungs with gross lesions of pneumonia. Fluorescence was observed to be most intense at PI weeks 4 to 6, with a tendency to decrease in intensity from PI weeks 8 to 12. This indicated that there may be a decrease in number of M hyopneumoniae cells in the more advanced stages of the disease. The use of a counterstain (chelated azo-dye) provided an excellent color contrast and permitted making unambiguous interpretation of results.