Table 1. H5N1 viruses characterized in mallard ducks.
| Isolation site | Virus | Inoculated dead/total | Contact dead/total | Pathogenicity | Days virus shed | No. amino acid differences in HA |
|---|---|---|---|---|---|---|
| Hong Kong | A/Hong Kong/156/97 | 0/2 | 0/2 | Low | 7 | 0 |
| A/chicken/Hong Kong/YU562/01 | 0/2 | 0/2 | Low | 7 | 0 | |
| A/chicken/Hong Kong/SSP94/03 | 0/2 | 1/2 | High | 11 | 0 | |
| A/chicken/Hong Kong/AP111/03 | 0/2 | 0/2 | Low | 11 | 0 | |
| Vietnam | A/mallard/Vietnam/16D/03 | 1/2 | 2/2 | High | 17 | 11 |
| A/duck/Vietnam/40D/04 | 1/2 | 0/2 | High | 13 | 4 | |
| A/Vietnam/1203/04 | 2/2 | 1/2 | High | 13 | 2 | |
| A/Vietnam/3046/04 | 0/2 | 0/2 | Low | 13 | 10 | |
| A/chicken/Vietnam/48C/04 | 1/2 | 0/2 | High | 17 | 6 | |
| A/chicken/Vietnam/133/04 | 1/2 | 1/2 | High | 11 | 2 | |
| Thailand | A/Thailand/1 (Kan-1)/04 | 0/2 | 0/2 | Low | 11 | 0 |
| China | A/chicken/Anhui-Chaohu/85/04 | 0/2 | 0/2 | Low | 17 | 2 |
| Indonesia | A/chicken/Pangkal Pinang/BPPV3/04 | 0/2 | 0/2 | Low | 13 | 0 |
| Singapore | A/duck/Singapore/3/97 (H5N3) | 0/2 | 0/2 | Low | 7 | 0 |
Two 4- to 6-week-old mallard ducks were inoculated with 106 EID50 of virus and placed after 4 hours with two contact ducks. The small number of ducks tested was because of the space constraints of the biosafety level 3+ facilities. High pathogenicity, at least one duck died; low pathogenicity, no ducks died. Days virus shed indicates the greatest number of days virus was detectable in at least one duck (inoculated or contact). All viruses that were shed at late time points were isolated from the cloaca. The number of amino acid differences in HA is a comparison of the HA gene sequence of virus shed by one duck at the latest time point and the HA gene sequence of the original virus sample. Changes occurred throughout the HA structure, with some occurring within antigenic sites. No changes were observed to occur within the multibasic cleavage site.