Table 1.

Properties of egg-adapted SD0 strainsa

VirusEgg passage at which positive hemagglutination was detectedNA stalk insertion
No. of amino acids insertedOrigin of gene insertion
0EA1222PB2
7EA1210PB2
10EA1013PB1
18EA818PB2
21EA1020NP
2EA120NAb
5EA80NA
14EA120NA
19EA120NA
25EA100NA
  • a Approximately 107.3 PFU of SD0 virus (1 ml) were injected into 10-day-old embryonated chicken eggs. After 2 days of incubation at 35°C, egg allantoic fluid was harvested and tested for viral growth by hemagglutination assays. Viruses were serially passaged by inoculating the eggs with undiluted allantoic fluid until hemagglutination was observed. The passage at which hemagglutination was first observed is shown. Only strains that yielded positive hemagglutination are indicated. The NA stalk insertion was detected by sequencing the NA gene.

  • b NA, not applicable.