Pathogenicity of Chlamydia psittaci after serial passage in chicken embryos

Abstract The virulence in pregnant ewes of a single strain of Chlamydia psittaci was tested after the following treatments: (a) 110 serial passages in chicken embryos (CE) incubated at 37 C, and (b) 7 CE passages at 37 C followed by 10 CE passages at 40 C. Neither treatment caused significant reduction in abortions (P > 0.3) nor incidence of ewes shedding chlamydia in placentas or vaginal discharges (P > 0.5) compared to ewes inoculated with the original virulent strain.