EXPERIMENTAL OTITIS-MEDIA IN CHINCHILLAS FOLLOWING NASAL COLONIZATION WITH TYPE-7F STREPTOCOCCUS-PNEUMONIAE - PREVENTION AFTER VACCINATION WITH PNEUMOCOCCAL CAPSULAR POLYSACCHARIDE

Chinchillas were colonized intranasally with type 7F S. pneumoniae and pneumococcal otitis media developed in > 50% of the animals during the 1st wk after negative middle ear pressure (-25 mm Hg) was briefly applied. Chinchillas (23) were vaccinated s.c. with the capsular polysaccharide of type 7F S. pneumoniae to determine whether vaccination could prevent development of experimental otitis media. Following vaccination, 14 animals seroconverted with at least a 2-fold rise in serum antibody [Ab] concentration; 9 vaccinated animals did not seroconvert. All 23 vaccinated animals and all of 42 unvaccinated control animals became colonized after intranasal inoculation with pneumococci. Only 1 (7%) of the vaccinated seroconverting animals developed pneumococcal otitis media, whereas 26 (62%) of the control animals developed middle ear infection with type 7F pneumococci. Of 9 vaccinated non-seroconverting animals, 4 (44%) developed pneumococcal otitis media. Protection was associated with high levels of serum Ab prior to intranasal inoculation. Higher Ab levels were found in sterile middle ear effusions than in S. pneumoniae-infected effusions. Vaccination with type 7F pneumococcal capsular polysaccharide significantly reduced the incidence of pneumococcal otitis media following intranasal inoculation of type 7F S. pneumoniae in chinchillas.