Histopathological analysis in placentas of ewes infected with Chlamydia abortus showing different gross lesion severity

Abstract

The placenta plays a vital role in nutrient exchange between the mother and fetus. In pregnant ewes, Chlamydia abortus infection causes suppurative necrotising placentitis, impairing this function. While gross placental lesions are observable, microscopic analysis is required for detailed characterisation. This study investigated the histopathological changes in placentas showing different severities of visible damage from C. abortus-infected ewes. This study investigated histopathological changes in placentas from ewes experimentally infected with C. abortus, grouped (n = 3 per group) by the extent of visible lesions: Low (0–25 %), Medium (40–60 %), and High (85–100 %). Formalin-fixed placentas were randomly sampled for histopathology and immunohistochemistry (IHC). In the Low group, the placentas showed mild to moderate focal suppurative placentitis. Medium group placentas exhibited severe multifocal suppurative necrotising placentitis with vascular thrombosis, while the High group exhibited severe, diffuse, suppurative necrotising placentitis with vascular necrosis and mineralisation. IHC for chlamydial lipopolysaccharide showed a higher presence in the trophoblast in the Medium group than in the Low or High groups. The histopathological parameters were standardised and statistically analysed to investigate each parameter's relative impact on the disease's pathogenesis. The findings suggest that ischemic necrosis, due to vascular lesions such as vasculitis, mural necrosis, and thrombosis driven by the host response to chlamydial antigens, has a greater impact on pregnancy outcome than cell lysis associated with the release of chlamydial elementary bodies. Reduced perfusion and inflammation-associated oedema increase the thickness of the maternofetal interface, compromising fetal nutrient exchange and fetal survival.