PREGNANCY FAILURE FOLLOWING VAGINAL INFECTION OF SHEEP WITH CHLAMYDIA-PSITTACI PRIOR TO BREEDING

Enzootic abortion in sheep, caused by Chlamydia psittaci, has been ass ociated with pregnancy failure in most sheep-producing countries, Late -term abortions or the birth of weak low-birth-weight lambs occurred f ollowing primary C. psittaci infection in pregnant ewes, However, the mode by which C. psittaci can be transmitted among sheep has not been established. The present study was designed to determine whether the v aginal tracts of nonpregnant ewes were susceptible to C. psittaci infe ction and whether such infections had an impact during the next pregna ncy. At day 0 of the estrus cycle, the vaginal tracts of 10 nonpregnan t ewes were inoculated with C. psittaci and 10 ewes were exposed by su bcutaneous injection, The ewes were bred 6 weeks postinfection. Five e wes from the vaginally infected group and four from the subcutaneously infected group were reinfected by subcutaneous injection at day 60 of gestation. Pregnancy outcomes and antibody responses to infection wer e compared with that of ewes that were infected with C. psittaci, eith er subcutaneously or intravaginally, for the first time during pregnan cy and with that of noninfected control ewes. Subcutaneous infection o f nonpregnant ewes did not cause subsequent pregnancy failure; rather, this provided protection against abortion following reinfection durin g pregnancy, As expected, abortions or the birth of weak lambs was obs erved in those ewes that received primary C. psittaci infection by eit her route during pregnancy. Similarly, abortion or the birth of weak l ambs was a consequence of vaginal inoculation prior to breeding, there by confirming the susceptibility of the vaginal mucosa to infection an d demonstrating the potential for venereal transmission.