Pathogenicity for turkeys of Chlamydia psittaci strains belonging to the avian serovars A, B and D.

Four groups of 20 specific pathogen-free turkeys kept in isolators were exposed to aerosols of one of four Chlamydia psittaci strains. These were strain 92/1293 (avian serovar D), strain 84/55 (avian serovar A), the Texas Turkey strain (avian serovar D) and strain 89/1326 (avian serovar B). A further group of four specific pathogen-free turkeys consisted of sham-infected controls. The birds were observed daily for clinical signs. At daily intervals for 10 days and then twice weekly up to 34 days post-infection, one bird in each group was killed and examined for gross and microscopic lesions. Clinical signs, macroscopic and microscopic lesions were most severe in turkeys infected with strains 92/1293 and 84/55, and there was some mortality. Signs and lesions were less severe in the group infected with the Texas Turkey strain and there was no mortality. The turkeys infected with strain 89/1326 developed only mild clinical disease and lesions. Thus, differences in pathogenicity for turkeys were shown not only between strains belonging to different serovars, but also between strains within a single serovar.