Table 2.

Mortality ratio and average clinical scores, monkeys inoculated by the intrathalamic route with ACAM1000 or Dryvax^® and necropsied on Day 16 after infection.

Study	Group (test article)	Dose log10 pfu	No. monkeys	No. (%) illa	No. (%) dead	No. (%) severe histopathologyb
1	ACAM1000	6.0	2	0 (0)	0 (0)	0 (0)
		7.0	2	0 (0)	0 (0)	0 (0)
		8.0	2	0 (0)	0 (0)	0 (0)
2	ACAM1000	7.1	6	0 (0)	0 (0)	0 (0)
	Dryvax®	7.7	6	3 (50)	3 (50)	3 (50)

^aA clinical scoring system was used to assign each animal a daily numerical score. Signs of encephalitis, such as paresis, incoordination, lethargy, tremors or spasticity were assigned numerical values for severity by the following grading method: 0 = No clinical signs of encephalitis; 1 = Rough coat, not eating; 2 = High pitched voice, inactive, slow moving; 3 = Shaky movements, tremors, in coordination, limb weakness; 4 = Inability to stand, limb paralysis, moribund or dead. Animals euthanized due to illness deemed too severe to permit further observation under humane conditions were given a score of 4 on the day of euthanasia and a score of 4 from the day after euthanasia through Day 16. Animals that died were given a score of 4 from the day of death to Day 16. The mean clinical score for each monkey was the average of the animal's daily score; since animals were evaluated twice daily, the higher daily score was used. The clinical score for a group was the mean of the individual animal clinical scores. In Study 2, one Dryvax^®-treated animal was found dead on Day 4, and two additional Dryvax^®-treated animals underwent unscheduled euthanasia due to declining health status on Day 6. Clinical signs in these animals included decreased activity levels (observed as low food consumption, decreased activity, hunched appearance, and/or lethargic), tremors, seizures and convulsions, and loss of coordination. The 3 monkeys that developed clinical signs had individual mean scores of 3.1, 3.3 and 3.4. The group mean score for this treatment group was 1.8. None of the ACAM1000 monkeys showed signs of illness, and the group mean score was 0.4.

^bBrain sections examined included cerebral cortex, basal ganglia (two levels), thalamus and midbrain, upper medulla and cerebellum, lower medulla and cerebellum, low medulla, and the cervical and lumbar spinal cord enlargements. Evidence of severe meningitis was noted histologically in the 3 early death Dryvax^®-treated animals in Study 2. Mild signs of residual meningitis, such as edema and small areas of cellular infiltration (mostly by lymphoid and monocytic cells), were also noted in the remaining three Group 1 animals and 5/6 Group 2 animals. There was no degeneration or necrosis of neurons, and there were no neuronophagic foci. No accumulations of bacteria were found in brain sections from animals showing the most severe signs of meningitis, and there were no signs of demyelination. The characteristics of the neuropathological lesions are consistent with previous studies of vaccinia virus, which causes nonpurulent meningitis and brain edema in monkeys by, Morita et al.²⁴