Time-related Pathological Changes in Horses Experimentally Inoculated with Equine Influenza A Virus.
To investigate the pathology of equine influenza, necropsy of 7 horses experimentally infected with equine influenza A virus (EIV) subtype H3N8 was conducted on post-infection days (PID) 2, 3, 7, and 14. Histopathologically, rhinitis or tracheitis including epithelial degeneration or necrosis with loss of ciliated epithelia and a reduction in goblet cell numbers, was observed in the respiratory tracts on PIDs 2 and 3. Epithelial hyperplasia or squamous metaplasia and suppurative bronchopneumonia with proliferation of type II pneumocytes were observed on PIDs 7 and 14. Viral antigen was detected immunohistochemically in the epithelia of the nasal mucosa, trachea, and bronchi on PIDs 2 and 3. The sodA gene of Streptococcus equi subsp. zooepidemicus, a suspected cause of suppurative bronchopneumonia, was detected in paraffin-embedded lung tissue sections, but only on PIDs 7 and 14. These findings suggest that damage caused to ciliated epithelia and goblet cells by EIV infection results in secondary bacterial bronchopneumonia due to a reduction in mucociliary clearance.
Epizootic Research Center, Equine Research Institute, the Japan Racing Association, 1400-4 Shiba, Shimotsuke-shi, Tochigi 329-0412, Japan.
Masanori
M
Muranaka
Epizootic Research Center, Equine Research Institute, the Japan Racing Association, 1400-4 Shiba, Shimotsuke-shi, Tochigi 329-0412, Japan.
Takashi
T
Yamanaka
Epizootic Research Center, Equine Research Institute, the Japan Racing Association, 1400-4 Shiba, Shimotsuke-shi, Tochigi 329-0412, Japan.
Yoshinari
Y
Katayama
Epizootic Research Center, Equine Research Institute, the Japan Racing Association, 1400-4 Shiba, Shimotsuke-shi, Tochigi 329-0412, Japan.
Hidekazu
H
Niwa
Racehorse Clinic, Miho Training Center, the Japan Racing Association, Ibaraki 300-0415, Japan.
Kazuomi
K
Oku
Epizootic Research Center, Equine Research Institute, the Japan Racing Association, 1400-4 Shiba, Shimotsuke-shi, Tochigi 329-0412, Japan.
Tomio
T
Matsumura
Department of Veterinary Pathology, School of Veterinary Medicine, Kitasato University, Aomori 034-8628, Japan.
Toshifumi
T
Oyamada
equine influenza A virus; equine respiratory disease; experimental infection