Chlamydiosis (Enzootic Abortion of Ewes) and risks in lambing season
Background
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 abortion. 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 not known with certainty. 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. Where 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.
By its nature 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 infection from ewes appears to be very unusual.
Very few reports of C. abortus in pregnant women in England and Wales are received each year by the Health Protection Agency’s Centre for Infections (CfI). In one or two cases per year (maximum 5 cases in 1986), this is associated with abortion or stillbirth. Since 1980, one maternal death associated with this infection has been reported.
In routine laboratory testing, and hence in reports to HPA CfI, no distinction is made between avian and mammalian (ovine) Chlamydophila abortus (Chlamydia psittaci). The avian strain is not confined to psittacine birds but is common in (for example) in feral pigeons. However, with the exception of one case, the severe form of the disease associated with human abortion has been due to the mammalian strain.
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 Chamydophila, and micro-immunofluorescence or whole cell inclusion immunofluorescence tests are needed to confirm the diagnosis of with C. abortus. Serological tests to distinguish avian and mammalian strains of C. abortus may be available on a research basis.
Chlamydophilia abortus is sensitive to macrolide antibiotics, and a 2 week course of erythromycin 500mg 4 times daily can be given if the patient is seen at an early stage. The effectiveness of this treatment in preventing the development of more serious disease has not been established. Azithromycin is a suitable alternative. The organism is also sensitive to tetracyclines and these are probably the drug of choice in more severe disease despite the general reservations about use of tetracyclines during pregnancy.
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
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
Chlamydiosis or EAE is the commonest cause of infectious abortion in sheep. Defra laboratories diagnosed the infection in 1551 reported incidents in 1995. This was the highest number in the 1991-2002 period. In 2005 it was diagnosed in 464 incidents of reported abortion and accounted for 36% of the reported incidents of abortion where a diagnosis was made. Each confirmed case generally represents an outbreak and the total number of sheep affected is therefore considerably higher. Some estimate may be gained from the fact that 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. Chlamydophilia abortus is the most common cause of abortion in lowland ewes, especially under intensive farming conditions.
A live vaccine for use in sheep is available. However, it should not be handled by pregnant women or women of childbearing age.
