Which organism is associated with enzootic abortion of ewes?

• A. Campylobacter fetus
• B. Chlamydia psittaci (enzootic abortion of ewes)
• C. Listeria monocytogenes
• D. Brucella ovis

Answer: (D)

Enzootic abortion of ewes is caused by a chlamydial organism, most classically Chlamydia abortus (historically grouped with Chlamydophila abortus; in older nomenclature you may see it referred to as Chlamydia psittaci). This intracellular bacterium localizes in the placental tissues, causing placentitis and fetal death, and is shed in placental fluids, which leads to contagious abortions within a flock, often in late gestation. Other organisms listed can cause reproductive issues in sheep, but not the enzootic abortion pattern: Campylobacter fetus tends to cause abortion outbreaks as well but is a different etiologic pattern; Listeria monocytogenes can cause abortion with systemic signs and is linked to poor silage; Brucella ovis mainly causes epididymitis in rams. The key idea is that the classic agent for enzootic abortion of ewes is the chlamydial organism Chlamydia abortus.