Abstract
Background: Chlamydia abortus and Chlamydia pecorum are important causes of abortion in small ruminants, and C. abortus is also zoonotic. Published Turkish data on chlamydial abortion in sheep and goats are almost exclusively serological, and C. pecorum has not previously been investigated in Turkish small ruminants.
Aims: To determine the presence of C. abortus and C. pecorum in ovine and caprine abortions and stillbirths using histopathology, immunohistochemistry (IHC) and nested PCR, and to characterise the associated lesions.
Methods: Necropsies were performed on 66 aborted fetuses and stillborn lambs (n = 44) and kids (n = 22) over three lambing/kidding seasons (2017–2020). Lung, heart, liver, kidney, spleen, intestine, stomach, brain, cerebellum, thymus and, in seven cases, placenta were examined by histopathology, IHC (Chlamydia spp. and C. abortus) and nested polymerase chain reaction (PCR) (Chlamydia spp., C. abortus, C. pecorum). Associations between species and positivity, and between season and species among positive cases, were assessed by Fisher's exact test.
Results: Chlamydia spp. was detected by IHC and/or PCR in 35/66 cases (53%); C. abortus in 32/66 (48%); and C. pecorum, reported here for the first time in Turkish small ruminants, in 4/66 (6%). IHC and PCR agreed closely (93% for Chlamydia spp., 90% for C. abortus). Lung and intestine showed the highest positivity, followed by kidney and liver; placenta, brain, stomach and thymus were rarely or never positive. Lesions were non-specific and frequently absent despite confirmed infection, with no significant difference between lambs and kids (p = 0.44).
Conclusion and recommendation: C. abortus, and to a lesser extent C. pecorum, are present in the Turkish small ruminant population. Because chlamydial infection often produces no diagnostic lesion, IHC and/or PCR examination of lung, intestine, kidney and liver should be performed routinely in suspected chlamydial abortion, regardless of histopathological findings.

Key words: Chlamydia abortus; Chlamydia pecorum; enzootic abortion; immunohistochemistry; PCR; Turkey