Experimental assessment of the pathogenicity of two avian influenza A H5 viruses in ostrich chicks (Struthio camelus) and chickens.

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.