An epizootic of pneumococcal infection occurred in inbred guinea pig colonies.

Epizootiological observations were made on an outbreak of pneumococcal infection occurred in 14 inbred guinea pig colonies during January to October, 1981. Monthly incidences of diseased animals ranged from 16.6 to 0%, showing the highest rate in the first month of the occurrence. Affection rates were remarkably different according to guinea pig strains, being 75% in JY-1 but 0% in JYG and Strain 2. Affected animals showed ruffled fur, dry-dirty noses, emaciated abdomen and dyspnea, and some of them were resulted in death. At necropsy, the fibrinopurulent pneumonia, pleuropneumonia and pleuritis were found as the major pathological features, and in addition, the fibrinopurulent pericarditis and peritonitis with a large amount of exudate were also observed in some cases. Streptococcus pneumoniae was isolated from nearly all the affected organs, and also from the external nares and trachea. Isolation rate from the external nares was especially high, thus 97.1% of infected guinea pigs including healthy carriers were detected by cultivation of nasal swab samples. Carrier rates of healthy animals were gradually increased from 17.2% in April to 36.5% in October, but the organism was not detected from JYG strain at all. During the observation period, vaccination, advance of weaning age of animals and administration of high vitamin C dose were taken as preventive measures of the epizootic, but no remarkable effect was obtained. The same diseased conditions were successfully produced in Hartley guinea pigs by experimental nasal infection of a pneumococcal strain isolated from this epizootic.