Performance of gross lesions at postmortem for the detection of outbreaks during the avian influenza A virus (H7N7) epidemic in The Netherlands in 2003

A total of 123 submissions (on average, five birds per submission) from poultry flocks with a suspicion of an infection with highly pathogenic avian influenza virus were investigated at postmortem during the 2003 epidemic in The Netherlands. A total of 86 of these submissions were from infected flocks (positive submissions), and 37 submissions were from non-infected flocks (negative submissions). Peritonitis was the most frequently (62%) recorded pathological finding in positive submissions, followed by tracheitis (43%), oedema of the neck and/or wattles (12%) and (petechial) haemorrhages in the proventriculus (4%). A total of 17% of the positive submissions consisted of birds without any macroscopic lesion. The pathological lesions observed in our study do not fully comply with descriptions in literature, especially the lack of haemorrhagic changes in tissues and low prevalence of oedema of the neck, comb and wattles. It is recommended that if peritonitis, or tracheitis, or oedema of the neck and/or wattles or (petechial) haemorrhages in the proventriculus is observed at postmortem examination, especially if accompanied by an anamnesis describing acute and high mortality in a flock, this should consistently result in follow-up action to exclude highly pathogenic avian influenza in the differential diagnosis as cause of the disease problems by testing tissue samples with an avian influenza-specific laboratory test at the avian influenza reference laboratory.