Seminário de doenças infecto-contagiosas

CHAPTER

2.8.8.

SWINE INFLUENZA

SUMMARY
Swine influenza is a highly contagious viral infection of pigs. Swine influenza virus (SIV) infections cause respiratory disease characterised by coughing, sneezing, nasal discharge, elevated rectal temperatures, lethargy, breathing difficulty, and depressed appetite. In some instances, SIV infections are associated with reproductive disorders such as abortion. Clinical signs and nasal shedding of virus can occur within 24 hours of infection. Morbidity rates can reach 100% with SIV infections, while mortality rates are generally low. Secondary bacterial infections can exacerbate the clinical signs following infection with SIV. Transmission is through contact with SIV-containing secretions such as nasal discharges and aerosols created by coughing or sneezing. Identification of the agent: Virus identification is best accomplished by collection of samples within 24–48 hours after development of clinical signs. The animal of choice is an untreated, acutely ill pig with an elevated rectal temperature. Virus can readily be detected in lung tissue and nasal swabs. Virus isolation can be conducted in embryonated chicken eggs and on continuous cell lines. Isolated viruses can be subtyped using the haemagglutination inhibition (HI) and the neuraminidase inhibition tests, or by reverse transcription-polymerase chain reaction assays. Immunohistochemistry can be conducted on formalin-fixed tissue and a fluorescent antibody test can be conducted on fresh tissue. Enzyme-linked immunosorbent assays (ELISA) are commercially available for detection of type A influenza viruses. Serological tests: The primary serological test for detection of SIV antibodies is the HI test conducted on paired sera. The HI test is subtype specific. The sera are generally collected 10– 21 days apart. A four-fold or greater increase in titre between the first and second sample is suggestive of a recent SIV infection. Additional serological tests that have