Experimental Sendai virus infection in laboratory rats. I. Virus replication and immune response.

Sixty 5 to 8 week old Sprague-Dawley (Crl:CD(SD)BR) rats were inoculated intranasally with 2000 egg infectious doses of egg-propagated Sendai virus. Virus was recovered from the upper respiratory tract and lungs on days 1 through 8 post-inoculation (PI). Serum antibody responses were measured for 12 rats over a 9 month period PI. Antibody was first detected at 7 days, peaked at 21 days, and was detected in 5 of the 12 rats at 9 months. A cell-mediated response, as measured by lymphocyte blastogenesis, also was detected at 7 days and peaked at 21 days, but was not detected at 6 months PI. Lung and serum interferon (IFN) was first detected at 3 hours and peaked at 6 hours, but was not detected by 160 hours. Lung IFN levels were 4 to 10 times those in the serum. These studies indicate that pathogenesis of Sendai virus infection in the rat is similar to that reported in the mouse, but that there are differences in the kinetics of both viral replication and morphologic changes, as described in the companion paper.