Susceptibility of LSH hamsters to intraperitoneal inoculation with Legionella pneumophila

The guinea pig is the most widely used animal model in the study of Legionellosis. The hamster should also be considered, since it acquires virtually no spontaneous epidemic lung infection, possesses similar cellular immune components observed in other mammals, has a normal body temperature identical to that of man, and is readily available for laboratory investigation. We studied the pathologic findings of four 12 week old inbred London School of Hygiene (LSH) hamsters inoculated intraperitoneally with 0.2 ml of 10(9) organisms per ml suspension of a viable Philadelphia 1 strain of Legionella pneumophila. Four LSH hamsters (control group) received 0.2 ml of sterile phosphate buffered saline, intraperitoneally. All animals of the test group became clinically ill and two of the four spontaneously expired on days 1 and 2 after inoculation. The remainder were sacrificed on day 3. In three out of four animals of the test group, a suppurative peritonitis and an interstitial pneumonitis were observed. It was characterized by infiltrates of neutrophils and macrophages. The test group also exhibited acute splenitis, including microabscesses, and two of four test animals showed hepatic congestion, vacuolization of hepatocytes, and microabscesses. None of the controls appeared sick or died after three days, and neither gross nor microscopic lesions were found at autopsy. Culture results documented L pneumophila in lung and spleen of all test animals and the absence of organisms in the control group. Hence, the LSH hamster is rapidly infected with the Philadelphia 1 strain of L pneumophila given intraperitoneally, and pathological changes can be readily observed. The findings of our study add hamsters to the list of animals susceptible to intraperitoneal infection by L pneumophila.