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Chlamydial abortion is the most commonly diagnosed cause of infectious abortion in sheep in the UK and was responsible for 46% of cases submitted to veterinary investigation centres between 1995 and 2003 (data supplied by VIDA). The disease is caused by a highly specialised bacterium called Chlamydophila abortus which is part of a family of bacteria known as Chlamydiaceae. Chlamydiaceae are widespread in nature and are responsible for a range of diseases in wild and domestic animals and birds, including lung, eye and reproductive tract infections. In man Chlamydia trachomatis is the leading cause of preventable blindness and sexually transmitted disease in the world.
Infection
During pregnancy, C. abortus spreads to the womb of infected sheep where it causes inflammation in the placenta (afterbirth). This may lead to death of one or more of the lambs or to the birth of weak lambs. Sheep pick up infection via contact with infected ewes and their lambs at lambing time. Discharges, dead lambs and placentas from aborting ewes are heavily contaminated with the bacterium. If ewes are in early pregnancy when exposed to infection then they may abort that year, however, if they are in late pregnancy then infection may remain dormant (silent) until the next pregnancy when abortion may then occur. Ewe lambs may also become infected and abort in their first pregnancy. Ewes which have aborted due to C. abortus develop immunity and will not usually abort again due to this cause.
Disease
Abortions due to C. abortus typically occur in the last few weeks of pregnancy. Work at Moredun has shown that regardless of when sheep become infected, the organism does not cause disease until after 90 days of pregnancy. It multiplies in cells of the placenta instigating an intense inflammatory response. In chlamydial abortion the placenta is usually dark red, thickened and will often have dirty yellow material sticking to the membrane between the button-like cotyledons.
The typical manifestation of chlamydial abortion is the appearance of stillborn lambs accompanied by inflamed placentas one to two weeks before the expected start of lambing. However, a chlamydial infection can also produce full-term stillborn or weak lambs and it is not uncommon for an infected ewe to have one dead lamb along with one or more live, weak or healthy lambs. Ewes commonly seem healthy following abortion although they may have a dirty vulval discharge for several days afterwards and some may occasionally go on to become sick due to inflammation in the womb.
Diagnosis
The key to diagnosing Chlamydophila infection is to submit aborted lambs with their placentas to the local veterinary laboratory for investigation. Your own veterinary surgeon may also advise submitting blood samples from aborting ewes.
Control of Chlamydial Abortion
The selection of a suitable control strategy for chlamydial abortion depends on the infection status of the flock. Veterinary advice should be sought regarding the best approach for your situation.
Preventing Spread of Disease
During an outbreak of disease, abortion material and contaminated bedding should be disposed of effectively (e.g. by burning) and aborted ewes should ideally be isolated from the rest of the flock for 6 weeks. These measures should help prevent the spread of infection to other animals within the flock. In flocks which are free of infection, replacements should be purchased from 'EAE accredited' flocks.
Vaccination
There are three vaccines commercially available to control chlamydial abortion; Mydiavac® (Novartis Animal Health), Enzovax®, (Intervet UK) and CEVAC Chlamydophila® (CEVA Animal Health Ltd). Your veterinary surgeon will be able to advise you as to which product would be most suitable for use on your farm. The use of a vaccination programme is an effective way of reducing the incidence of disease in a flock over several years by rendering animals immune to infection.
Treatment
During an outbreak of abortion due to Chlamydophila then treatment with long-acting oxytetracycline (20 mg per kg body weight) will reduce the severity of infection. For best effect it should be given at 95 to 105 days of pregnancy. A second injection two weeks later will further reduce losses. However, some ewes will still abort and infection may still spread to other animals in the flock resulting in future disease problems.
Human Infection
Chlamydophila abortus is a particular risk to the pregnant woman and her developing foetus. Infection may result in foetal death and also cause severe illness in the mother. Pregnant women should therefore avoid all involvement with lambing ewes and should not handle contaminated clothing from those working with lambing ewes or new-born lambs. People with a problem with their defence (immune) system (i.e. immunosuppressed or immunocompromised) must also avoid contact with potential sources of infection at lambing time.
In an emergency please telephone (01793) 522483 (24hrs).
Drove Veterinary Hospital, 252 Croft Road, Swindon, Wiltshire SN1 4RW. |
