Chlamydia - Enzootic Abortion of Ewes (EAE)
- What is Chlamydiosis?
- What effects does EAE have in human pregnancy?
- Is there any risk of later consequences?
- What are the symptoms of the disease in humans?
- Who is at risk?
- How is the infection acquired?
- How common is this infection in man?
- What tests are available to confirm the diagnosis?
- Is there any effective treatment?
- Is there any vaccine?
- Are subsequent pregnancies likely to be at any risk?
- Is the infection common in sheep in the UK?
- What are the manifestations of disease in sheep?
- Is a vaccine available for use in sheep?
1. What is Chlamydiosis?
Chlamydiosis is an infection caused by Chlamydophilia abortus. Chlamydiosis is thought to be transmitted by inhalation of aerosols and dusts heavily contaminated with Chlamydophilia abortus (formerly Chlamydia psittacci), which is the agent of enzootic abortion in ewes (EAE). It can cause serious disease in the unborn child, leading to stillbirth or abortion.
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2. What effects does EAE have in human pregnancy?
The main effects are severe, sometimes life-threatening, disease in the mother, and stillbirth or abortion.
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3. Is there any risk of later consequences?
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).
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4. What are the symptoms of the disease 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 3-8 days after the onset of the symptoms.
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5. 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, including veterinary surgeons, and their immediate families.
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 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.
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6. How is the infection acquired?
The route of transmission to man is not known with certainty. Inhalation of aerosols and dusts heavily contaminated with Chlamydophila abortus (formerly called Chlamydia psittaci), the agent of enzootic abortion in ewes (EAE), 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.
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7. How common is this infection in man?
Human infection with Chlamydophilia abortus (Chlamydia psittaci) infection from ewes appears to be very unusual and very few reports of it in pregnant women in England and Wales are received each year by the Health Protection Agency's Communicable Disease Surveillance Centre (CDSC). 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- CDSC, 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 (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.
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8. What tests are available to confirm the 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 (Chlamydia psittaci) and C. pneumoniae, and microimmunofluorescence or whole cell inclusion immunofluorescence tests are needed to confirm the diagnosis of with Chlamydophila abortus (Chlamydia psittaci). Serological tests to distinguish avian and mammalian strains of Chlamydophila abortus (Chlamydia psittaci) may be available on a research basis.
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9. Is there any effective treatment?
Chlamydophilia abortus (Chlamydia psittaci) is sensitive to macrolides 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.
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10. Is there any vaccine?
There are no effective chlamydial vaccines for human use available at present.
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11. Are subsequent pregnancies likely to be at any risk?
Following enzootic abortion, sheep generally acquire long-lasting immunity and give birth normally in subsequent seasons. Very limited data suggests that this is also the case in humans.
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12. Is the infection common in sheep in the UK?
Yes. 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 period 1991-2002. In 2002 it was diagnosed in 508 incidents of reported abortion and accounted for 44% 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 Chlamydophila abortus (Chlamydia psittaci) and about 1 million lambs are aborted or stillborn each year.
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13. What are the manifestations of disease in sheep?
Characteristically, the production of dead or weak lambs in the last two or three weeks of pregnancy. Chlamydophilia abortus (Chlamydia psittaci) is the most common cause of abortion in lowland ewes, especially under intensive farming conditions.
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14. Is a vaccine available for use in sheep?
Yes. A live vaccine is available. However, it should not be handled by pregnant women or women of childbearing age.
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