Influenza alone and in sequence with pneumonia due to Streptococcus pneumoniae in the squirrel monkey.

Squirrel monkeys (Saimiri sciureus) inoculated intratracheally with 10(4.2)-10(8.2) egg median infectious doses (EID50) of type A influenza virus (H3N2) responded with clinical illness including such signs as fever, sneezing or coughing, coryza, and increased respiratory rates. Necropsy studies performed six days after inoculation revealed bronchopneumonia in addition to a mild tracheitis. Squirrel monkeys given 10(5)-6 x 10(8) colony-forming units (cfu) of Streptococcus pneumoniae intratracheally died four to six days later after developing severe illness characterized by fever, bacteremia, lethargy, anorexia, coughing, labored breathing, and bronchopneumonia. Monkeys given 770 cfu of S. pneumoniae responded with less severe symptoms and survived. Four squirrel monkeys inoculated with 10(8.2) EID50 of virus and then 102 hr later with 770 cfu of S. pneumoniae developed severe disease; three of the four animals died within 40 hr. At necropsy these monkeys had more extensive and severe bronchopneumonia than was seen in monkeys infected with either organism alone.