Enzootic abortion in sheep: a review

Enzootic abortion of ewes (EAE), also known as chlamydial abortion or ovine enzootic abortion, is caused by Chlamydophila abortus. This bacterium has a complex lifecycle, varying between extracellular and intracellular stages. High numbers of the infectious extracellular stage are found in the aborted fetuses, fluids and membranes. Ewes become infected by ingestion or inhalation, although diagnosis is not possible until 90 days into the subsequent pregnancy, with the outcome dependent on the ewe's immune status (see Table 1).

Adapted from Sargison, 2009

EAE remains the most common cause of abortion in the UK, responsible for 42% of diagnosed infectious fetopathies in England in 2020 (Animal and Plant Health Agency (APHA), 2020), and has been for several decades. Lambs may be stillborn or compromised with additional losses through perinatal disease. A 2007 survey of UK sheep farmers revealed 33.8% of respondents reported cases of EAE (Longbottom et al, 2013); 40.7%, 16.7% and 8.6% of lowland, hill and pedigree flocks respectively reported cases. 47.6% of larger flocks (>150 ewes) reported cases versus 9.4% of smaller flocks.