Guidelines for diagnosis of swine influenza
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This article is intended to describe the adequate sample collection, the laboratory procedures/techniques, the expected results and their interpretation for diagnosis of influenza infection in swine, serving as a support for field veterinarians. In live pigs, the samples to be taken are nasal secretions, oral fluids and blood. For dead pigs, preference should be given to samples of cranioventral lung consolidation. Nasal discharge and chilled lung fragments are used for detection of virus (virus isolation -VI) or viral nucleic acids (conventional RT-PCR and real-time RT-PCR). Samples should not be frozen, because the virus is inactivated at -20°C. Molecular characterization of isolates is performed by phylogenetic analysis of gene sequences obtained by DNA sequencing. Serum is used for the detection of antibodies using hemagglutination inhibition (HI) test and ELISA. Oral fluid may be used for either antibody (ELISA) or viral detection. Fragments of lung fixed in 10% formaldehyde are used for histopathological analysis to identify bronchointerstitial pneumonia, and for immunohistochemistry (IHC) for antigens. For a successful diagnosis, sampling should be preferably performed in the acute phase of the disease to improve chances of virus detection. The best options to perform the diagnosis of influenza A in a swine herd are RT-PCR and VI from nasal swabs or oral fluid in live pigs and/or lung tissue for RT-PCR, VI or IHC in dead pigs. Serological tests are of very limited diagnostic value and are useful only to determine the immune status of the herd, notindicating clinical disease, because antibodies are detected after 7-10 days post infection (subacute phase). The diagnosis of influenza is important to evaluate the involvement of this agent in the complexof respiratory diseases in pigs. Furthermore, the isolation of influenza virus is essential for monitoring the main subtypes circulating ina given region or country, as well as for the detection of potential new viral reassortants, because influenza is considered a zoonosis.
author list (cited authors)
Schaefer, R., Rech, R. R., Silva, M. C., Gava, D., & Ciacci-Zanella, J. R.