Mycoplasma hyorhinis infection in early cases of mycoplasmal pneumonia in swine and evaluation of diagnostic assays

Abstract

RESUMO.-[Infecção por Mycoplasma hyorhinis em casos precoces de pneumonia micoplásmica em suínos e comparação entre técnicas diagnósticas.] A pneumonia micoplásmica causada por bactérias do gênero Mycoplasma é uma enfermidade de grande importância para indústria suinícola, sendo ainda controverso o papel desempenhado por Mycoplasma hyorhinis nessa doença. A confirmação da presença dessas bactérias bem como a identificação de seus papéis em doenças respiratórias continua sendo um grande desafio. Os objetivos desse estudo foram comparar diferentes técnicas, em especial a de hibridização fluorescente in situ (FISH), para diagnóstico de micoplasmoses respiratória em suínos naturalmente infectados e avaliar a presença do M. hyorhinis em casos precoces de pneumonia micoplásmica. Mycoplasmal pneumonia is an important disease in the pig industry. Due to the controversial role of Mycoplasma hyorhinis in this disease, confirmation of the presence of this bacterium and the identification of its roles in respiratory disease remain major challenges. The objectives of this study were to evaluate the presence of M. hyorhinis in early cases of mycoplasmal pneumonia and to determine the usefulness of fluorescent in situ hybridization (FISH) for the diagnosis of respiratory mycoplasmosis in naturally infected pigs. Ninety M. hyopneumoniae and/or M. hyorhinis-infected lung tissue samples based on diagnostic mosaic (DM) were used. The average age of the animals was 116 and 57 days (P<0.01) for groups 1 (positive-M. hyopneumoniae only) and 2 (positive-M. hyorhinis only), respectively. These findings suggest that development of lesions caused by M. hyorhinis occurs earlier than for M. hyopneumoniae. Using the DM as the gold standard, the sensitivity and specificity of FISH for M. hyopneumoniae were 75 and 100%, respectively, and were 40 and 73.3% for the immunohistochemistry (IHC). The sensitivity and specificity of FISH for M. hyorhinis were 76.7 and 100%, respectively. These findings demonstrate that FISH can be a useful tool for diagnosing mycoplasmosis. Viral antigens (PCV2 or influenza A) were detected in 53.3% (16/30) of the samples in group 2 (M. hyorhinis-PCR positive) and 13.3% (4/30) of the samples in group 1 (M. hyopneumoniae-PCR positive). This finding indicates that the association of M. hyorhinis and viral infection in nursery pigs likely starts due to a viral immunosuppressive condition.

The Role of Pathology in the Diagnosis of Swine Respiratory Disease

“…Histopathological tools can also be used to detect bacterial nucleic acids or antigens, for example, to diagnose respiratory mycoplasmosis or A. pleuropneumoniae infections [61][62][63]. In the lung, M. hyopneumoniae is localized on the surface of bronchial and bronchiolar epithelial cells [64], while A. pleuropneumoniae binds to respiratory epithelial cells of the terminal bronchioles and to pneumocytes [10].…”