Infectious abortion is a major flock health problem for sheep farmers. The most common cause is Enzootic Abortion of Ewes (EAE) which accounted for 43% of all diagnoses made at veterinary investigation centres in one recent study. The second most common cause is toxoplasmosis which accounted for 27% of diagnoses in the same study. Both of these diseases can be controlled with vaccines, amongst other measures, and both cause disease in humans and are a risk to pregnant women in particular.

Enzootic Abortion is caused by a bacterium called Chlamydophila abortus. It is carried in ewes and infection is spread at lambing time when ewes are exposed to aborted lambs and infected placentas. The bacterium incubates in infected ewes which usually abort the following year. Put simply, ewes pick up the infection one year and abort the next. Abortion “storms” can result from Chlamydophila infection when it is not unknown for up to a third of the flock to lose their lambs. When this happens it is usually because infected ewes have been introduced to a clean flock prior to lambing the previous year. Abortion losses can be reduced in the face of an outbreak by injecting oxytetracycline antibiotic at 95 to 105 days of pregnancy and then two weeks later.

Toxoplasmosis is a protozoan parasite. The definitive host is the cat and ewes become infected by eating food which has been contaminated with cat faeces. Cats produce millions of eggs (oocysts) when they first become infected and shed them for 1-2 weeks. These eggs can survive in the environment for up to 18 months under the right conditions. Toxoplasma can infect all warm bloodied animals, including humans, and pregnant woman are most at risk. Humans can also become infected by eating or handling undercooked meat or by coming into contact with cat faeces. The in-feed coccidiostat decoquinate can be used to reduce losses due to toxoplasmosis in the face of an outbreak. It does not cure infections but will reduce the multiplication and spread of the parasite within the host and reduce losses to abortion. Toxoplasmosis also causes abortion storms if feed heavily contaminated in a naïve flock.

The Vaccines

The vaccine for Enzootic Abortion is Enzovax® and for Toxoplasmosis is Toxovax®.

Toxovax®

• The dose is 2ml and is given into the muscle. Only one injection is required.
• Toxovax® is given between 3 weeks and 4 months before tupping.
• Toxovax® can be used from 5 months of age in ewe lambs.
• Toxovax® should not be used in pregnant animals.
• Revaccination is needed after 2 years to maintain full immunity.
• Toxovax® is available as 20 or 50 dose vials.

Reducing the risk to human health

To reduce the risk of human infection, and abortion in women in particular, consider the following control measures:

• Pregnant woman should not work in the lambing shed
• Pregnant woman should not handle clothing used in the lambing shed.
• Wear disposal gloves when handling aborted lambs or placentas.
• Shepherds should wash their hands and arms thoroughly in warm, soapy water after assisting with a lambing.
• Never give the kiss of life to a lamb. Weakly lambs are particularly risky and apparently healthy lambs may be infected.
• See your doctor if you feel ill around lambing time especially if you are working with a flock where infectious abortion has been diagnosed
• Young children should not be taken into the lambing shed
• Older children should be discouraged from petting lambs and keep them away from their faces. They should keep their hands away from their mouths and wash them in warm, soapy water when they leave the lambing shed.

Most of the other, less common, causes of abortion in ewes, including listeriosis, campylobacter, salmonellosis and Q fever are also infectious to human.

Control of ovine abortions

• Isolate ewes which have aborted. They should remain isolated for a minimum of 7 to 10 days and until discharges have dried up.
• Identify aborted ewes so they can be blood sampled later if necessary.
• Retain afterbirths and aborted foetuses for laboratory investigation. Samples should be submitted fresh.
• Laboratories usually achieve a diagnosis if they receive sufficient, good quality samples.
• Remove dead lambs and afterbirths promptly and cover the area with plenty of clean straw. Dispose of the foetus and placental tissues carefully by burial or burning.
• Purchase replacement ewes from flocks that are accredited free of EAE under the SAC Premium Health Scheme.
• Prevent cats from contaminating sheep feed with faeces, including hay, where possible.