Table 2. Histological examination of the lungs of mice.

Days	1			3			6
#*	1	2	3	1	2	3	1	2	3
b240	++/++	+++/+++	++/++	+++/+++	++/++	+++/+++	+++/+++	+++/+++	+++/+++
saline	++/++	+++/+++	+++/+++	+++/+++	+++/+++	+++/+++	+++/+++	+++/+++	ND†

Nine mice per group were infected with 10 MLD₅₀ of CA04 virus and three mice per group were euthanized on days 1, 3, and 6 post-infection. The extent of pneumonia and viral antigen expression was evaluated by using a distribution scoring system. 0%, -; 0% < 40%, +; 40% < 60%, ++; and 60% < 100%, +++.

*The number of the individual animals.

^†Not determined.