Pregnant women in lambing season: advice

Advice on the main infectious hazards for pregnant women in contact with sheep and other animals

Chlamydiosis (EAE)

Chlamydiosis (EAE) is an infection caused by Chlamydophila abortus (formerly known as Chlamydia psittaci). Chlamydiosis is thought to be transmitted by inhalation of aerosols and dusts heavily contaminated with the organism. It can cause serious disease in the unborn child, leading to stillbirth or miscarriage.

Effects on human pregnancy

The main effects 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).

Symptoms in humans

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, renal and hepatic complications. It is these cases that are most commonly associated with stillbirth or abortion, which generally occurs 3 to 8 days after the onset of the symptoms.

Who is at risk

Only women who have close contact with ewes at the time of aborting or giving birth, with new-born lambs and with placentae or products of conception. Infection has also been associated with handling of clothing and boots contaminated by contact with infected animals.  By its nature the risk is limited mainly to those actively working with sheep and their immediate contacts.

Although EAE is known to be present in the sheep flocks in some cases, it is often overlooked in the first year in which it arrives in 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 often a diagnosis is not made until then.

How the infection is acquired

The route of transmission to people is not known with certainty. Inhalation of aerosols and dusts heavily contaminated with Chlamydophila 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.

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

Tests to confirm diagnosis

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 Chlamydophila abortus and C. pneumoniae, and microimmunofluorescence or whole cell inclusion immunofluorescence tests are needed to confirm the diagnosis of with Chlamydophila abortus.  Serological tests to distinguish avian and mammalian strains of Chlamydophila abortus  may be available on a research basis.


Chlamydophilia abortus is susceptible to antibiotics. If you think you have been infected or at risk, you should seek advice from your medical practitioner.

There are no effective chlamydial vaccines for human use available at present.

Subsequent pregnancies

Following enzootic abortion, sheep generally acquire long-lasting immunity and give birth normally in subsequent pregnancies. Very limited data suggests that this is also the case in humans.

Effect on sheep

EAE is the commonest cause of infectious abortion in sheep. Characteristically, the production of dead or weak lambs in the last two or three weeks of pregnancy. A live vaccine is available for sheep. However, it should not be handled by pregnant women or women of childbearing age.


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