Table 2. Virulence and replication of four HPAI H5N1 viruses in adult mallards.
| Challenge virus* | No. ducks | Clade | Mortality/morbidity† | Mean day of shedding onset‡ | Mean day of symptom onset§ | Day of death|| | Mean shedding duration¶ | Mean shedding duration until death¶ | Mean peak titre## | Cumulative mean virus shedding** | HI titre†† | Productively infected‡‡ |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| HK1161 | 4 | 2.3.2.1b | 75/100 | 1.0±0.0 | 4.8±0.6 | 4, 6, 8, – | 6.0±1.2 | 5.0±1.0 | 4.6±0.5 (5) | 21.1±3.3 | 15 (1/1) | 4/4 |
| Bulg38WB | 4 | 2.3.2.1c | 0/50 | 1.0±0.0 | 4.5±0.5 | –, –, –, – | 4.8±0.5 | na | 4.3±0.5 (1) | 17.1±1.7 | 43±14 (4/4) | 4/4 |
| LaoLH2 | 4 | 2.3.4.1 | 0/0 | 1.0±0.0 | na | –, –, –, – | 3.8±0.8 | na | 3.5±0.5 (1) | 11.5±3.9 | 60±12 (4/4) | 4/4 |
| HKAP156 | 3 | 2.3.4 | 0/0 | 1.0±0.0# | na | –, –, – | 2.5±0.4 | na | 2.0±1.0 (1) | 4.7#±2.3 | 73±7 (3/3) | 3/3 |
| HK1161 Bulg38WB | 8 | 2.3.2.1 | 75/38 | 1.0±0.0 | – | – | 5.4±0.6 | – | 3.5±0.4 (5) | 19.1±1.9 | – | 8/8 |
| LaoLH2 HKAP156 | 7 | 2.3.4 | 0/0 | 1.0±0.0# | – | – | 3.3±0.6 | – | 3.3±0.4 (1) | 8.6±2.7 | – | 7/7 |
*Abbreviations as in Methods.
†In per cent; morbidity as detected via conjunctivitis, depression, or neurological symptoms (ataxia, seizure, disorientation). Some animals died/were found dead without symptoms having been observed.
‡Mean day p.i. ± standard error. Oropharyngeal shedding. Limit of detection was 0.75 log10 EID50 ml−1. #One animal did not shed.
§Mean day p.i. ± standard error. For mean day of symptom onset, death was included as a symptom.
||Either found dead in cage or euthanized due to moribund state.
¶Shown are mean days ± standard error of oropharyngeal shedding. Swabs were titrated every day or every other day; we considered that a bird that shed from day 1 to day 5 but not on day 7 and with no data for day 6 shed 4.5 days. The bird in the HKAP156 group that did not shed was excluded from the shedding duration calculation. na, not applicable.
##In log10 EID50 ml−1. Limit of detection was 0.75 log10 EID50 ml−1. (Day of peak titre p.i.)
**Cumulative mean virus shedding over time (area under the curve) as log10 EID50 of oropharyngeal swabs.
††Mean haemagglutination inhibition titre to homologous antigen ± standard error (animals with HI titre ≥10/surviving animals).
‡‡By virus shedding and/or seroconversion.