Abortion and subsequent excretion of chlamydiae from the reproductive tract of sheep during estrus.

Chlamydia psittaci serovar 1 infection in pregnant sheep typically causes abortion or the birth of weak lambs. Eight sheep that experienced chlamydia-induced abortion during their first pregnancy were successfully rebred yearly for the past 2 years. Chlamydia-specific lipopolysaccharide was detectable for approximately 3 weeks in vaginal swabs taken from the experimentally infected sheep following abortion. There was no evidence of chlamydiae in vaginal, placental, or neonatal samples obtained immediately after each subsequent successful pregnancy. Sera collected from the experimentally infected sheep had persistent, high antibody levels to C. psittaci, suggesting continued exposure of the immune system to the organism. Examination of vaginal specimens obtained during various stages of the estrus cycle revealed detectable levels of chlamydiae only when the animal was near ovulation. Chlamydiae were not detected in swabs from sheep that did not experience abortion. Enhanced chlamydial excretion during the periovulation period of sheep may provide sufficient stimulation of the immune system to account for the persistent antibody response. Furthermore, the association between estrus and chlamydial shedding has important implications for transmission of infection to other ewes during breeding.