Chlamydia abortus: epidemiology, transmission and prevention
Source: gov.uk (2025-07-15)

Information for health professionals on the epidemiology, transmission and prevention of Chlamydia abortus which can cause stillbirth or abortion in humans.

This content was originally produced by Public Health England (PHE). This content is now owned and managed by the UK Health Security Agency (UKHSA)

Chlamydia abortus (formerly called Chlamydia psittaci) is a cause of abortion and foetal loss in sheep, cattle and goats in many countries around the world. Enzootic abortion in sheep is also known as ovine enzootic abortion (OEA) or enzootic abortion of ewes (EAE).

Infected and aborting ewes excrete the organism in large amounts in diseased placenta, uterine discharges and faeces.

Human infections follow inhalation of infected material from livestock, and may lead to respiratory disease.

Although human infections may not have symptoms, where symptoms do occur, they are commonly of a ‘flu-like’ illness: 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.

Characteristic symptoms in pregnancy include:
- systemic illness with disseminated intravascular coagulation (a haemorrhagic disorder)
- renal complications
- hepatic complications
These cases are most commonly associated with stillbirth or abortion, which generally occurs 3 to 8 days after the symptoms start.

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.

Transmission

The route of transmission to humans is uncertain, but inhaling aerosols and dusts heavily contaminated with C. abortus is the likely route of infection. 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
- new-born lambs
- 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 1 or 2 cases of C. abortus each year in pregnant women in the UK.

The annual number of human cases of C. abortus is uncertain as routine serological testing does not distinguish between C. abortus and other Chlamydia species.

Diagnosis and treatment

Diagnosis rests chiefly on clinical suspicion. 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 Chlamydia, 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.

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

Contact the respiratory and vaccine preventable bacteria reference unit (RVPBRU) (https://www.gov.uk/guidance/rvpbru-reference-and-diagnostic-services) for test details.

Prevention of infection in pregnancy

Defra, Department of Health, PHE and the Health and Safety Executive issue regular reminders about avoiding infections during the lambing season (https://www.gov.uk/government/news/pregnant-women-advised-to-avoid-animals-that-are-giving-birth).

To avoid the possible risk of infection, pregnant women are advised:
- do not help to lamb or milk ewes
- avoid contact with aborted or new-born lambs or with the afterbirth
- do not handle clothing, boots etc which have come into contact with ewes or lambs
- do not handle the live vaccine used to protect sheep
Potentially contaminated clothing will be safe to handle after being washed on a hot cycle.

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.

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

The HSE publish guidance on protecting farmers and farm workers from zoonoses (http://www.hse.gov.uk/agriculture/topics/zoonoses.htm).

The Advisory Committee on Dangerous Pathogens (ACDP) produces guidance on a range of dangerous pathogens-related subjects, including ‘Infection risks to new and expectant mothers in the workplace’ (http://www.hse.gov.uk/pubns/books/infection-mothers.htm).