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Home Topics Infectious Diseases Infections A-Z Chlamydophila abortus Chlamydiosis (Enzootic Abortion of Ewes) and risks in lambing season

Chlamydiosis (Enzootic Abortion of Ewes) and risks in lambing season


Chlamydiosis is an infection caused by Chlamydophilia abortus (formerly called Chlamydia psittaci). Chlamydiosis is thought to be transmitted by inhalation of aerosols and dusts heavily contaminated with C. abortus which is the agent of enzootic abortion in ewes (EAE). It can cause serious disease in the unborn child, leading to stillbirth or abortion.

Human disease

In humans infection may be asymptomatic but, where symptoms occur, they are commonly of a 'flu-like nature with headache, chills, fever, joint pains and non-productive cough. Photophobia, vomiting, sore throat and myocarditis may also occur. In pregnancy, a more severe form of the disease may occur, the majority of reported cases occurring between 24 and 36 weeks. This is characterised by systemic illness with disseminated intravascular coagulation (a haemorrhagic disorder), renal and hepatic complications. It is these cases that are most commonly associated with stillbirth or abortion, which generally occurs 3-8 days after the onset of the symptoms

The main effects of chlamydiosis in pregnancy are severe, sometimes life-threatening, disease in the mother, and stillbirth or miscarriage. If the pregnancy survives the acute infection, there appears to be no risk of long-term problems. There is no evidence that this infection can result in abnormalities in the baby when it is born (congenital malformation). Subsequent pregnancies are unlikely to be at risk of any abnormality.


The route of transmission to humans is not known with certainty, however inhalation of aerosols and dusts heavily contaminated with C. abortus appears to be the likely route of infection. The organism is concentrated in the uterus of pregnant sheep, and the infected placenta and uterine discharges are the most potent sources of the infectious agent. Contact with aborting sheep, sheep at risk of abortion, dead lambs and placentae are thus considered to represent a risk for humans. When lambing and handling of pregnant and post-partum ewes takes place indoors, the risk of human exposure to the organism may be greater than in open pastures.

The risk is limited mainly to those actively working with sheep, including veterinary surgeons, and their immediate families. Women are at risk if they have close contact with ewes at the time of aborting or giving birth, with new-born lambs, or with placentae or products of conception. Infection has also been associated with handling of clothing and boots contaminated by contact with infected animals.

Epidemiology of disease in the UK

Human infection with C. abortus from ewes appears to be very unusual.

It has been generally accepted that there are only one or two cases of C. abortus each year in pregnant women in the UK, however the number of human cases of C. abortus occurring annually is uncertain as routine serological testing does not distinguish between C. abortus and other Chlamydophila species. Diagnosis of C. abortus is dependent primarily on clinical suspicion in a person with positive serology for chlamydial infection and relevant exposure to sheep/lambing.

Diagnosis and treatment

Diagnosis rests chiefly on clinical suspicion and treatment should be started on that basis. Diagnosis is generally confirmed by serological testing but this requires testing of both acute and convalescent sera. The complement fixation test (CFT) does not distinguish between different species of Chlamydophila, and more specialised tests (such as micro-immunofluorescence or whole cell inclusion immunofluorescence) are needed to confirm the diagnosis of C. abortus infection. Serological tests to distinguish avian and mammalian strains of C. abortus may be available on a research basis.

Chlamydophilia infections can be treated effectively with a number of antibiotics. There are no effective chlamydial vaccines for human use available at present.

Prevention of infection in pregnancy

To avoid the possible risk of infection, pregnant women are advised that they should:

  • not help to lamb or milk ewes
  • avoid contact with aborted or new-born lambs or with the afterbirth
  • avoid handling clothing, boots etc which have come into contact with ewes or lambs. Potentially contaminated clothing will be safe to handle after being washed on a hot cycle

They should also avoid handling the live vaccine that is used in sheep.

Pregnant women should seek medical advice if they experience fever or influenza-like symptoms, or if concerned that they could have acquired infection from a farm environment.

Chlamydophila infection in sheep in the UK

C. abortus continues to be the most commonly diagnosed infectious cause of abortion in sheep (and also causes abortion in goats and cattle).

In 2012, C. abortus was identified as the cause of abortion in 539 (34.2%) of sheep and goat submissions in which a diagnosis was reached. The equivalent figures for 2011 were 451 (40%) diagnoses from relevant sheep and goat submissions. C. abortus was not confirmed in abortion material from cattle in 2012 or in 2011, but it is an occasional diagnosis, and three cases were diagnosed in cattle in Great Britain during 2010. Each confirmed case generally represents an outbreak in the source flock or herd and the total number of animals affected is therefore considerably higher.

Between 20-50% of abortions in sheep are thought to be due to C. abortus and about 1 million lambs are aborted or stillborn each year. Although EAE is known to be present in the sheep flocks, in some cases it may be overlooked in the first year in which it is introduced to a flock. Typically, it is introduced into a flock by infected breeding females. Some of these suffer abortion in the first year and infect much of the rest of the flock but these secondary cases do not suffer abortion until the following year and a diagnosis is not made until then. Characteristic manifestations of disease in sheep are the production of dead or weak lambs in the last two or three weeks of pregnancy.

A live vaccine for use in sheep is available. However, it should not be handled by pregnant women or women of childbearing age.

[content reviewed 3 January 2014)