Properties of a Chlamydia psittaci isolated from muskrats and snowshoe hares in Canada

Abstract

An etiologic agent of epizootic chlamydiosis of muskrats and snowshoe hares, designated as strain M56, was placed in C. psittaci species on the basis of insensitivity to sulfadiazine and d-cycloserine and the formation of diffuse, irregular, glycogen-free inclusions. Pathogenicity studies indicated a high virulence, a moderate toxicity, and a broad host range. Experimental infections tended to be pantropic. In addition to the muskrat and snowshoe hare, susceptible mammals were laboratory mice, guinea pigs, hamsters, and domestic rabbits. In adult domestic rabbits, infections were highly lethal, whereas mortality was rare in young rabbits. After 2 months, the agent persisted in the cerebrum, joints, and internal eye of several young rabbits in spite of relatively high titers of neutralizing antibodies. Strong immunity to strain M56 was established by intravenous inoculation of the living agent in young rabbits. In addition to ricebirds, susceptible birds were domestic chicks, parakeets, and mallard ducklings. The facility with which this organism infects both birds and mammals is a sufficient reason for epidemiologists to search marshes and lakes where water birds and muskrats intermingle for nidi of infection. The relatively high rate of subclinical chlamydial infections in man in northern Canada may be attributable, in part, to this agent.