Sendai virus (SV) infection in aged BALB/c mice was evaluated as a nat
ural model for age-associated susceptibility to viral pneumonia. Young
(2 month-old) and aged (22-24 month-old) BALB/c mice were inoculated
intranasally with 100 median pneumonia doses (PD50) of SV and examined
at 6, 10, and 20 days by virus titration, immunohistochemistry, histo
pathology, and serology. The aged mice had significantly higher virus
titers in lung, prolonged infection, delayed development, and resoluti
on of pneumonia and significantly lower serum antibody titers. In a se
cond experiment, the responses of young mice were compared to intermed
iate-aged mice (11-13 and 17-18 months old). The intermediate-aged mic
e had some characteristics of young mice and others of aged mice. The
results indicate that SV infection can be used to study aging-associat
ed susceptibility to a pneumotropic virus in a natural host, and that
susceptibility of mice to viral pneumonia increases gradually during a
ging.