Infectious abortion in sheep

WHILE many organisms can cause sporadic, fatal infections of the ovine fetus, a smaller number have a particular ability to colonise the conceptus and cause characteristic syndromes of abortion. The aim of this article is to provide an update on infectious causes of abortion, focusing primarily on those that commonly occur in the UK. Of the protozoa, Toxoplasma gondii is a major cause of abortion in many sheep‐producing countries, including the UK, while Sarcocystis species and Neospora caninum also have the potential to cause fetal loss. Of the bacteria, Chlamydia psittaci is the major pathogen of pregnancy in the UK, as in parts of continental Europe; Campylobacter fetus fetus, Salmonella species, Listeria monocytogenes and Brucella melitensis can also cause severe losses, although the last does not occur in the UK. The rickettsia Coxiella burnetii probably infects the ovine placenta more often than is recognised, though fetal death is relatively uncommon, while abortion due to tickborne fever is secondary to the febrile response. The most important viral infection in the UK is border disease; Wesselsbron disease, bluetongue and Akabane virus disease occur outside the UK. All may attack the ovine fetus, damaging the developing central nervous system and sometimes also other systems such as the skeleton.