Experimental infection of pregnant ewes with Chlamydia pecorum.

Pregnant ewes were infected in midpregnancy with three isolates of Chlamydia pecorum derived from the feces of healthy lambs from three different farms. Oral infection, alone or together with Fasciola hepatica, did not result in tissue invasion, since all placental and fecal samples were negative for chlamydiae. Intravenous infection resulted in placental infection in 16 of 18 ewes in that chlamydiae were cultured from placentas or vaginal swabs. Two ewes bore dead lambs after a shortened gestation time. The chlamydiae isolated were all C. pecorum. There were no significant differences between the weights of the lambs from the infected groups and those from uninfected control ewes. Most ewes showed no serological evidence of infection by the complement fixation test; therefore, it is unlikely that the enteric subtype of C. pecorum is responsible for the cross-reactions sometimes seen in flocks being tested for C. psittaci infection.