Latest Briefing in Sustainability and Communities for 2012

Ovine chlamydiosis - the most common infectious cause of prenatal lamb death in the UK

Ovine Enzootic Abortion (OEA) (also known as Enzootic Abortion of Ewes (EAE) or ovine chlamydiosis) is caused by the bacterium Chlamydia abortus (formerly known as Chlamydophila abortus) and is one of the major infectious causes of abortion in sheep and goats worldwide, and the most common cause in the UK. The disease is considered to be ‘endemic’ in the UK as it is constantly present in the livestock population, but also ‘enzootic’ as it only affects a limited number of animals at any one time. The disease is a major health and welfare issue for the livestock industry with large economic implications amounting to tens of millions of pounds annually. Chlamydia abortus can also infect cattle, pigs and horses but disease outbreaks are much more sporadic and less frequent. Infection can also be passed from animal to human (zoonotic) in whom it can cause spontaneous abortion (miscarriage). It can also be potentially life-threatening for pregnant women, although reported cases of transmission are rare.

It is difficult to identify infection in individual animals within a flock, making the disease difficult to control. The first sign of infection is often the appearance of dead or live weak lambs in the last few weeks of pregnancy with visibly diseased placentas and a vaginal discharge of infective fluid, which can last for several days. The infected placentas, coats of dead lambs, contaminated bedding and vaginal discharges are the major sources of infection for other animals. In an extended lambing season uninfected ewes can pick up infection from another ewe and abort in the same lambing season. There is little evidence that the disease can be transmitted mechanically by rams.

The spread of disease is difficult to control as infection of a non-pregnant ewe only becomes apparent during pregnancy and it is currently impossible to identify infection in such animals through diagnostic testing. For this reason care must be taken when sourcing and introducing replacement stock. The introduction of only a few infected animals may be sufficient to lead to an abortion storm affecting up to 30% of ewes within two years. Once an animal has aborted it is considered immune to further disease, although it can still infect other animals. Although antibiotics can be used to reduce losses at the first signs of a problem they do not eradicate the disease. Thus, currently the most effective means of controlling infection is through the use of vaccination.

Published on 22 October 2012 in Sustainability and Communities , Food, health and wellbeing

Briefings in Sustainability and Communities for 2012