RESUMEN
The presumed route of human infection by Legionella pneumophila is inhalation. We investigated possible oral transmission of legionellosis in guinea pigs. Fifty-six guinea pigs (group 1) were given virulent L. pneumophila, serogroup 1, in drinking water. Fifty-nine guinea pigs (group 2) were inoculated with L. pneumophila via gastric intubation. Nineteen guinea pigs (group 3) were given heat-killed L. pneumophila in drinking water. Twenty-four guinea pigs (group 4, positive control) were inoculated intraperitoneally with L. pneumophila. Twenty-seven guinea pigs (group 5, negative control) were either intubated gastrically with phosphate-buffered saline or given drinking water without L. pneumophila. Sixty-six of 115 (57%) of the guinea pigs orally inoculated with viable L. pneumophila (groups 1 and 2) had a temperature greater than or equal to 103 degrees F and 8 of 115 (7%) had diarrhea, compared with 0 of 19 (0%) and 0 of 19 (0%), respectively, in group 3 and 1 of 27 (4%) and 0 of 27 (0%), respectively, in group 5. There were no fatalities in groups 1, 2, 3, and 5 compared with 15 of 24 (63%) in group 4. Groups 1, 2, and 4 consistently showed pneumonitis and splenitis. The pneumonitis of groups 1 and 2 was mild, predominantly interstitial, and mainly composed of macrophages; neither gross nor microscopic evidence of aspiration was seen. In group 1, 4 of 29 (14%) guinea pigs tested seroconverted to L. pneumophila compared with 0 of 7 (0%) in group 3 and 0 of 10 (0%) in group 5. In groups 1 and 2 combined, L. pneumophila was isolated from the lung of 5 of 57 (11%) guinea pigs and spleen of 5 of 47 (11%) guinea pigs compared with 0 of 14 guinea pigs in group 5. We conclude that viable L. pneumophila administered orally produces a self-limited febrile illness in guinea pigs.
