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Virus excretion, immune response, and, for chickens, deaths were recorded in 3-week-old ostriches and chickens inoculated by either the intramuscular or intranasal route with one of two influenza A viruses of subtype H5. One of the viruses, A/turkey/England/50-92/91 (H5N1) (50/92), was highly pathogenic for chickens causing 5/5 deaths by each route of inoculation. The other virus, A/ostrich/Denmark-Q/72420/96 (H5N2) (72420/96), isolated from ostriches in quarantine in Denmark during 1996, was of low pathogenicity for chickens, causing no clinical signs by either route of inoculation. No significant clinical signs were seen in any of the ostriches infected with either of the viruses by either route of infection. Both viruses were recoverable from both species up to 12 days post-infection, and low serological responses were detected in surviving infected ostriches and chickens at 21 days after inoculation.

A total of 146 of 506 ostriches (Struthio camelus) introduced into a quarantine in Denmark died within the first 23 days. The majority of deaths were in young birds up to 10 kg body weight. Avian influenza A viruses (AIVs) were isolated from 14 pools of organ tissues representing seven groups each of three or four ostriches, which died over the first 3 weeks. The AIVs were detected in respiratory tissues, kidneys and intestines. All were subtype H5N2. The intravenous pathogenicity index of each isolate for chickens was 0.0 and the four isolates examined each had the amino acid sequence -P-Q-R-E-T-R*G-L-F- at the cleavage site of the haemagglutinin protein, typical of non-pathogenic AIVs. In addition, an avirulent avian paramyxovirus type 1 virus was isolated from one pool of kidney tissues. Bacteriological examination gave no significant results. The most characteristic pathological findings were impaction of the proventriculus and gizzard, enteritis with stasis and multi-focal necrotic hepatitis.