STUDIES ON THE EARLY PHASE OF THE PATHOGENESIS OF OVINE ENZOOTIC ABORTION IN THE NONPREGNANT EWE

The initial phase of infection of non-pregnant sheep by Chlamydia psit taci (ovis) was studied by inoculating naive and previously exposed sh eep by the ore-nasal and subcutaneous routes with the BS isolate of C. psittaci (ovis). Naive animals exhibited a marginal rise in temperatu re and seroconversion was detected by enzyme-linked immunosorbent assa y (ELISA) as early as 9 days after inoculation. Chlamydaemia was detec ted using culture and an antigen detection ELISA. No faecal shedding o f chlamydiae was detected in ewes kept up to 3 weeks after infection. Although chlamydial antigen was demonstrated in epithelial cells or ly mphocytes in lungs, liver, spleen, kidney, abomasum,jejunum, tonsils a nd suprapharyngeal, mandibular, parotid and mesenteric lymph nodes of some of the naive sheep using an ELISA and streptavidin-biotin and imm unofluorescent staining techniques, the organism could not be cultured from these tissues. No chlamydial antigen was demonstrated in any of the tissues of the previously exposed sheep nor in uninoculated contro ls. It is concluded that previously infected sheep are capable of comp letely eliminating subsequent infection and that chlamydiae localize i n a variety of tissues of infected naive sheep, especially within epit helial cells and lymphocytes.