Table 3. Pathogenicity of avian and human H5N1 viruses in mice.

Viruses*	Deaths	Days to death	Lung titer	Brain titer	Kidney titer	Paralysis
A/Ck/HK/61.9/02	7/7	8	4.8 ± 0.29	No	No	No
A/Ck/HK/31.4/02	2/7	9	3.6 ± 0.38	1.8†	No	Yes (1/9)
A/Gs/HK/739.2/02	3/11	10	2.8 ± 0.5	3.25 ± 0.25	No	Yes (3/8, 3/9, 3/10)
A/HK/213/03	10/11	11	4.5 ± 0.5	4.0†	No	No

Groups of mice were inoculated intranasally with 50 μl of allantoic fluid containing ≈0.5 × 10^6.5 eID₅₀ of virus. Titers are expressed as the mean ± SD log₁₀ eID₅₀ per 0.1 ml of tissue homogenate. Deaths are expressed as the number of deaths per number inoculated, and paralysis is expressed as the number of mice with paralysis per number of days after inoculation.

^*Infectivity in embryonated chicken eggs for all viruses was 10^7.5 eID₅₀ per 0.1 ml.

^†Virus was detected and titered in the brain tissues of one paralyzed or dead mouse.