FIG. 2.

Cumulative incidence for neurologic disease induced by the parental viruses KP and KP41 as well as the six chimeric viruses over a 120-day period of observation. Mice were inoculated i.p. as neonates and followed for evidence of clinical neurologic disease. Mice were scored as positive at the first physical sign, which was generally an abnormality of reflex abduction of the hind limbs when mice were picked up by the tail. The numbers of mice followed for each group are as follows: KP, 30; KP41, 37; E⁵³K/L⁵⁶P, 39; R⁴³E, 70; G⁴⁴N, 24; R⁴⁷Q, 30; E⁵³K, 28; and L⁵⁶P, 27.