FIG. 4.

Titer of infectious virus recovered from virus-infected pigs. The amount of excreted infectious virus (TCID₅₀/milliliter) was determined from nasal swab samples obtained from each animal (designated by number in the key) infected with recombinant M5′ (A), parental (B), and rescuant R5′ (C) viruses. At day 0 p.i., the bar represents the titer of each virus inoculum given to the pigs. Starting at 2 days p.i., each bar represents the titer of virus excreted from the animals at the specified time points.