Table 1.
Protective efficacy of recombinant DEV vaccines against H5N1 lethal virus HB/49 challenge in ducksa
| Challenge time p.v. | Vaccine | Dose (PFU) | No. HI antibody positive/totalb (mean titer, log2) | No. of swabs showing shedding virus/total no. (titer in log10EID50/ml) on day p.c.c: |
No. surviving/ total | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| 3 |
5 |
7 |
||||||||
| Oropharyngeal | Cloacal | Oropharyngeal | Cloacal | Oropharyngeal | Cloacal | |||||
| 3 Days | rDEV-ul41HA | 105 | 0/11 | 3/8 (2.5 ± 1.5) | 3/8 (2.3 ± 1.1) | 1/6 (1.3) | 0/6 | 0/5 | 0/5 | 5/8 |
| rDEV-us78HA | 105 | 0/11 | 3/8 (1.9 ± 1.2) | 1/8 (1.3) | 0/6 | 0/6 | 0/6 | 0/6 | 6/8 | |
| DEV | 105 | 0/11 | 8/8 (2.9 ± 1.4) | 8/8 (2.4 ± 0.9) | / | / | / | / | 0/8 | |
| PBS | 0/11 | 8/8 (3.1 ± 1.3) | 6/8 (1.9 ± 0.6) | / | / | / | / | 0/8 | ||
| 1 wk | rDEV-ul41HA | 105 | 3/11 (1.3) | 0/8 | 0/8 | 0/8 | 0/8 | 0/8 | 0/8 | 8/8 |
| rDEV-us78HA | 105 | 3/11 (2.6) | 0/8 | 0/8 | 0/8 | 0/8 | 0/8 | 0/8 | 8/8 | |
| DEV | 105 | 0/11 | 8/8 (4 ± 0.5) | 8/8 (3.3 ± 0.4) | 1/1 (3.5) | 1/1 (2.3) | / | / | 0/8 | |
| PBS | 0/11 | 8/8 (3.1 ± 0.6) | 8/8 (3.0 ± 0.5) | / | / | / | / | 0/8 | ||
| 3 wk | rDEV-ul41HA | 105 | 3/11 (1.6) | 0/8 | 0/8 | 0/8 | 0/8 | 0/8 | 0/8 | 8/8 |
| rDEV-us78HA | 105 | 4/11 (1.7) | 0/8 | 0/8 | 0/8 | 0/8 | 0/8 | 0/8 | 8/8 | |
| DEV | 105 | 0/11 | 8/8 (3.5 ± 1.6) | 7/8 (2.7 ± 1.5) | / | / | / | / | 0/8 | |
| PBS | 0/11 | 8/8 (3.3 ± 0.8) | 8/8 (2.8 ± 0.5) | 2/2 (3.1 ± 0.5) | 2/2 (1.9 ± 0.9) | / | / | 0/8 | ||
| 3 Days | rDEV-ul41HA | 106 | 0/11 | 1/8 (1.8) | 0/8 | 0/8 | 0/8 | 0/8 | 0/8 | 8/8 |
| rDEV-us78HA | 106 | 0/11 | 0/8 | 0/8 | 0/8 | 0/8 | 0/8 | 0/8 | 8/8 | |
| DEV | 106 | 0/11 | 8/8 (2.1 ± 0.6) | 6/8 (1.5 ± 1.5) | 2/2 (2.9 ± 0.9) | 2/2 (2.1 ± 0.6) | / | / | 0/8 | |
| PBS | 0/11 | 8/8 (3.2 ± 1.2) | 6/8 (2.2 ± 0.6) | / | / | / | / | 0/8 | ||
| 10 wk | rDEV-ul41HA | 105d | 1/6 (3) | 1/6 (1.5) | 0/6 | 0/6 | 0/6 | 0/6 | 0/6 | 6/6 |
| rDEV-us78HA | 105d | 2/6 (1) | 0/6 | 0/6 | 0/6 | 0/6 | 0/6 | 0/6 | 6/6 | |
| rDEV-us78HA | 106 | 1/6 (1) | 0/6 | 0/6 | 0/6 | 0/6 | 0/6 | 0/6 | 6/6 | |
| PBS | 0/6 | 6/6 (3.3 ± 1.7) | 6/6 (2.6 ± 0.9) | / | / | / | / | 0/6 | ||
Four-week-old specific-pathogen-free ducks were used in these studies. The ducks were intramuscularly injected with one or two doses of DEV or recombinant DEVs as indicated or with PBS as a control (p.v. indicates postvaccination). They then were challenged intranasally with 100-fold DLD50 of the H5N1 virus HB/49 at different time points. Three ducks in each group, excluding those that were challenged at 10 weeks p.v., were euthanized on day 3 postchallenge (p.c.) to test for viral replication in organs (Fig. 4), and the remaining ducks in each group were monitored for virus shedding and death for 2 weeks.
Sera were collected from all ducks before challenge, and HI antibody titers were determined by using 0.5% chicken red blood cells. The titers shown are the means for the ducks that had detectable HI antibodies.
Swabs were collected from all of the available ducks on days 3, 5, or 7 p.c. for virus titration in eggs. The titer shown is the means ± standard deviations for the ducks that shed viruses. A backslash indicates that the animals had died by that time point.
Ducks were vaccinated with two doses of 105 PFU of the indicated recombinant DEVs at a 3-week interval.