FIG. 5.

Inoculation i.n. with the attenuated KyA strain is protective against subsequent challenge with the pathogenic EHV-1 strain RacL11. Groups of CBA mice were either uninfected (•) or infected i.n. with 2 × 10⁶ PFU of KyA (○). Two weeks following KyA infection, both groups of mice were infected i.n. with 1.5 × 10⁶ PFU of RacL11. On days 2 and 4 postchallenge, the lungs were removed and homogenized, and the amount of infectious EHV-1 was determined by standard plaque titration as previously described. Each dot represents the log PFU per lung determined from a single mouse. The horizontal bars represent the mean log PFU per experimental group.