Table 2

Transmissibility is dependent upon the type of hemagglutinin expressed by the virus

Virus used to infect indexaGene constellationbGrowth in contact micecHId% Infectede
PB2PB1PAHANPNAMNSNasal TurbinatesTracheaLung
Udorn3.96 ± 0.82.9 ± 0.181.32 ± 1.46640100
PR8<0.9f<0.9<0.9<100
PR8-Udorn HA + NAg4.8 ± 0.523.13 ± 0.35<0.9320100
PR8-Udorn HA3.95 ± 0.763.32 ± 1.10<0.91280100
PR8-Udorn NA<0.9<0.9<0.9<100
  • a Index mice were infected via the total respiratory tract route with 1,000 PFU of reverse-engineered viruses and cohoused with contact mice.

  • b Reverse-engineered viruses contained different combinations of A/Udorn/307/72 (Udorn) genes (gray) and A/PuetoRico/8/34 Mt Sinai lineage (PR8) genes (white). Shading indicates the presence of the gene.

  • c Four days after cohousing, the viral loads were measured in nasal turbinates, trachea, and lung of contacts and are expressed as mean log10 PFU/ml ± SD (n = 6).

  • d Hemagglutination-inhibiting (HI) antibody titers of contacts are reported as means ± SD (n = 3).

  • e Percentage of contacts containing virus in nasal turbinates (n = 6).

  • f Detection limit of the plaque assay.

  • g PR8-Udorn HA + NA, virus containing all genes from PR8 except for the HA and NA genes of Udorn; PR8-Udorn HA, virus containing all genes from PR8 except for the HA gene of Udorn; PR8-Udorn NA, virus containing all genes from PR8 except for the NA gene of Udorn.