Pathological changes in turkeys experimentally infected with different doses of A/ostrich/Italy/984/2000 H7N1 avian influenza virus

Following experimental inoculation of 3-week-old turkeys with different titres (106, 104, 103, 102 and 101 egg infectious dose (EID50)) of A/ostrich/Italy/984/2000 H7N1 highly pathogenic avian influenza virus (HPAIV), the selected tissues and organs were examined for pathological changes. Tissue samples from different organs that obtained from dead and sacrificed birds were fixed in 10% neutral buffer formaldehyde. Mortality of turkeys which inoculated with different doses of EID50 at different times post inoculation (PI) is as follows: 1) at 48 h PI (HPI): one, two and four turkeys inoculated with 103, 104 and 106 EID50, respectively 2) at 72 HPI: two, two and one turkeys inoculated with 102, 103 and 106 EID50, respectively 3) at 96 HPI: one and two turkeys inoculated with 102 and 104 EID50, respectively and 4) at 120 HPI: just one turkey inoculated with 104 EID50. Birds inoculated with 101 EID50 did not show any mortality. Seven days PI (DPI) the remaining birds were sacrificed. Postmortem examination of birds that died 48 HPI showed very severe hyperaemia and haemorrhage of the lung, slight swelling of kidneys and splenomegaly. Moderate to slight hyperaemia of the lung was observed in the birds sacrificed on day 7. Histopathology showed very severe haemorrhage and vasculitis in the lung, multifocal areas of degeneration and necrosis in the pancreas of birds inoculated with 106 EID50. Hyperaemia, haemorrhage, degeneration and vasculitis were also observed in the lung of birds from the other groups; however the severity of lesions correlated positively with the viral dose. The spleen, caecal tonsils and thymus showed extensive necrosis and lymphoid depletion, even in birds inoculated with 102 and 101 EID50 that were sacrificed 7 DPI, and some repopulation of the spleen was observed 7 DPI. Other organs including the kidneys and adrenal gland showed moderate to slight hyperaemia and necrosis. In conclusion, the lung vascular damage, lymphoid tissue destruction and necrosis were notable even with low viral doses.