Studies on the early phase of the pathogenesis of ovine enzootic abortion in the non-pregnant ewe.

The initial phase of infection of non-pregnant sheep by Chlamydia psittaci (ovis) was studied by inoculating naïve and previously exposed sheep by the oro-nasal and subcutaneous routes with the BS isolate of C. psittaci (ovis). Naive animals exhibited a marginal rise in temperature and seroconversion was detected by enzyme-linked immunosorbent assay (ELISA) as early as 9 days after inoculation. Chlamydaemia was detected using culture and an antigen detection ELISA. No faecal shedding of chlamydiae was detected in ewes kept up to 3 weeks after infection. Although chlamydial antigen was demonstrated in epithelial cells or lymphocytes in lungs, liver, spleen, kidney, abomasum, jejunum, tonsils and suprapharyngeal, mandibular, parotid and mesenteric lymph nodes of some of the naïve sheep using an ELISA and streptavidin-biotin and immunofluorescent 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 controls. It is concluded that previously infected sheep are capable of completely eliminating subsequent infection and that chlamydiae localize in a variety of tissues of infected naïve sheep, especially within epithelial cells and lymphocytes.