Transmission of avian influenza virus (H3N2) to dogs

Abstract

In South Korea, where avian influenza virus subtypes H3N2, H5N1, H6N1, and H9N2 circulate or have been detected, 3 genetically similar canine influenza virus (H3N2) strains of avian origin (A/canine/Korea/01/2007, A/canine/Korea/02/2007, and A/canine/Korea/03/2007) were isolated from dogs exhibiting severe respiratory disease. To determine whether the novel canine influenza virus of avian origin was transmitted among dogs, we experimentally infected beagles with this influenza virus (H3N2) isolate. The beagles shed virus through nasal excretion, seroconverted, and became ill with severe necrotizing tracheobronchitis and bronchioalveolitis with accompanying clinical signs (e.g., high fever). Consistent with histologic observation of lung lesions, large amounts of avian influenza virus binding receptor (SAalpha 2,3-gal) were identified in canine tracheal, bronchial, and bronchiolar epithelial cells, which suggests potential for direct transmission of avian influenza virus (H3N2) from poultry to dogs. Our data provide evidence that dogs may play a role in interspecies transmission and spread of influenza virus.

Figure 1

Phylogenetic relationship among hemagglutinin genes of canine influenza virus isolates. Tree of hemagglutinin genes from representative isolates from dog, human, bird, pig, and horse. Scale bar represents a difference of 5%. Red boxes indicate strains isolated in this study.

Figure 2

Body temperature, virus shedding, and antibody seroconversion after challenge with canine influenza virus. Body temperature was increased from 1 day postinoculation (dpi) and slowly decreased to normal temperature by 7 dpi. Virus shedding was detected from 1 dpi to 6 dpi by reverse transcription–PCR. However, the ELISA antibody titers increased after 6 dpi. Antibody titers were regarded as positive if percent inhibition (PI) was >50.

Figure 3

Histopathologic lesions in the trachea and lungs of control (A and C) or experimentally infected (B, D–F) dogs (A/canine/Korea/01/2007 [H3N2]) at different days postinoculation (dpi). A) Control dog at 9 dpi, showing normal pseudostratified columnar epithelium lining of the trachea; original magnification ×400. Hematoxylin and eosin (HE) stain. B) Influenza-infected dog at 9 dpi, showing necrotizing tracheitis characterized by necrosis (n), squamous metaplasia (s), and hyperplasia of the epithelium and nonsuppurative inflammation (c) in the connective tissue; original magnification ×400. HE stain. C) Control dog at 3 dpi, showing normal alveoli; original magnification ×200. HE stain. D) Influenza-infected dog at 3 dpi, showing severe diffuse necrotizing bronchitis and bronchiolitis with suppurative inflammation in the lumina; original magnification ×100. HE stain. E) Influenza-infected dog at 6 dpi, showing severe necrotizing bronchiolitis; original magnification ×200. HE stain. F) Influenza-infected dog at 6 dpi (serial section of E), showing large amounts of influenza A virus antigens (red stain; arrows) in the bronchiolar epithelium and lumen. Immunohistochemistry; Red Substrate (Dako, Carpinteria, CA, USA); Mayer’s hematoxylin counterstain. G) Influenza-infected dog at 9 dpi, showing severe necrotizing alveolitis with accumulation of necrotic cells in terminal bronchioles (tb) and alveoli (a); original magnification ×200. HE stain.

Figure 4

Lectin staining (red stain) for SAα 2,3-gal (avian influenza virus receptors) and SAα 2,6-gal (human influenza virus receptors) in canine trachea, bronchus, and bronchioles, together with porcine tissues as a positive control. Original magnification all x300. −, no staining; ±, rare or few positive cells; +, moderate numbers of positive cells; and ++, many positive cells.