Pathologic findings in dogs infected with newly emerged canine H3N8 influenza virus

Abstract

In 2004, investigation of an outbreak of a spontaneous respiratory disease in greyhound dogs in Jacksonville FL led to the isolation of an H3N8 influenza A virus (canine/FL/04). Gene sequence analysis indicates the virus was of equine origin. Subsequent respiratory disease investigation studies have demonstrated that closely related H3N8 canine influenza virus has become widely disseminated throughout the United States and is inducing serious respiratory disease both in racing greyhound dogs and in pet and animal shelter dog populations. Postmortem examinations were conducted on greyhound dogs in the initial disease outbreak and subsequently in pet and animal shelter dogs of varying breeds that were demonstrated to be canine influenza positive by RT-PCR and/or virus isolation. In addition, dogs were inoculated intratracheally with canine/FL/04 virus and studied at 5 and 14 days after inoculation. In all dogs studied, canine influenza virus infection was associated with severe erosive or hyperplastic tracheitis and bronchitis. Viral antigen was identified in epithelial cells lining trachea, bronchi and their glands and in macrophages. Budding virions were identified by transmission electron microscopy on the apical surface of bronchial ciliated epithelial cells in association with severe ciliary defects. In greyhound dogs, death following infection was associated with severe hemorrhagic pneumonia and hemorrhage throughout thoracic tissues. In spontaneous canine influenza infections, secondary bacterial pneumonia was common. Funded by State of Florida Pari-mutuel Trust Fundt