TABLE 2.
Nasal excretion of H5N1 avian influenza in pigsb
| Day | Swab viral titer (log10 EID50/0.1 ml) (SD)
|
|||||||
|---|---|---|---|---|---|---|---|---|
| A/Vt/1203/04
|
A/Ck/Vt/C-58/04
|
A/Dk/Th/D4AT/04
|
A/Gs/Th/G7CS/04
|
|||||
| Inoculated | Contact | Inoculated | Contact | Inoculated | Contact | Inoculated | Contact | |
| −1 | −a | − | − | − | − | − | − | − |
| 1 | 2.75 (0.5) | − | 3.75 | − | 2.75 | − | 3.75 | − |
| 2 | 3.33 (0.3) | − | 3.75 | − | 3.33 | − | 3.75 | − |
| 3 | 1.33 (0.3) | − | 2.33 | − | 1.75 | − | 2.75 | − |
| 4 | − | − | 0.75 | − | − | − | 01.33 | − |
| 5 | − | − | − | − | − | − | − | − |
| 6 | − | − | − | − | − | − | − | − |
−, no detectable virus.
The viruses used in this study were isolated in embryonated chicken eggs as described previously (7). We selected one human and one avian isolate from Vietnam (A/Vt/1203/04 and A/Ck/Vt/C-58/04) and two avian isolates from Thailand (A/Dk/Th/D4AT/04 and A/Gs/Th/G7CS/04). Sequence analysis revealed the four viruses to have 99.1% to 99.8% homology in their hemagglutinin genes (data not shown). Yorkshire white weanling pigs (approximately 4 weeks old) that were determined to be free of detectable influenza virus by serologic testing were inoculated intranasally with 3.3 × 106 EID50 of virus in a volume of 1.0 ml (divided between two plastic syringes for separate inoculation of each nostril). An uninoculated littermate was housed in an isolator with each inoculated pig to test for pig-to-pig transmission of virus. Because of the small size of the isolators in our BSL3+ facility, we attempted to obtain the maximum possible information by using four individual, albeit genetically very similar (5), viruses to infect small numbers of animals. In most cases, only one pig was inoculated with each virus. However, the human virus (A/Vt/1203/04) group was retested separately to confirm our results. The pigs’ temperatures and food consumption were recorded daily, beginning 2 days before inoculation and ending on day 6 after inoculation (end of study). Each nostril was swabbed daily, and virus was titrated in embryonated chicken eggs. All viruses and animal experiments were handled in a BSL3+ facility approved by the U.S. Department of Agriculture, and the research staff wore fitted HEPA filter masks.