Toxoplasmosis and Risks in Lambing Season

Toxoplasmosis is a zoonotic infection (an infection that can be transmitted between animals and humans) caused by the parasite Toxoplasma gondii. Pregnant women and individuals with a depressed immune system are most at risk from infection with T. gondii.

Toxoplasmosis in pregnancy

In the UK, toxoplasmosis is thought to affect about 2 per thousand pregnancies. Less than half of these cases are transmitted to the unborn baby. Even when transmission occurs, the majority of babies (90-95%) have no symptoms. If a woman becomes infected with toxoplasma for the first time while she is pregnant, although she may not experience any symptoms the infection can be passed on to her unborn child and cause congenital toxoplasmosis. How severe this congenital disease is depends on the stage of pregnancy at which the mother is infected. It is rare for a mother to become infected early in the pregnancy, however if this occurs the effect on the foetus may be severe, and lead to complications such as miscarriage, stillbirth or birth defects. Babies whose mothers are infected during the last 28 weeks of pregnancy very rarely experience any problems or symptoms at birth. Some affected babies may develop eye disease in later life. Subsequent pregnancies are not at risk.

Transmission and prevention

Transmission of the organism can occur from hand-to-mouth contact with faeces of infected cats, contaminated soil, poorly washed garden produce and ingestion of cysts in undercooked meat, and direct contamination of cuts and grazes. Contact with infected sheep at lambing may thus result in either contamination or ingestion.

The main way to prevent toxoplasmosis is to take general hygiene precautions to avoid ingesting the parasite. If contact with ewes at lambing time is unavoidable, open wounds (cuts, grazes etc,) should be covered with waterproof dressings, and hands should be thoroughly washed after handling animals to prevent the possibility of infection. Pregnant women should also avoid contact with the live vaccine used in sheep.

Diagnosis and treatment

Blood tests can be carried out to detect antibodies to the organism. Since these may reflect infection in the past, additional confirmatory tests have to be carried out to see whether the infection is recent. Toxoplasmosis is usually a mild, self-limiting disease and does not usually require specific treatment when it occurs in normal, healthy people. A range of anti-toxoplasma drug treatments are available for those at greater risk of severe toxoplasmosis. There is no vaccine available for human use

Infection in sheep in Great Britain

Toxoplasmosis is the second most common cause of abortion in sheep in Great Britain, after Chlamydophila (EAE). The number of incidents recorded each year by Defra laboratories between 1999 and 2008 ranged from 197 to 490. In 2008 it was diagnosed in 201 reported incidents.

There are no clinical manifestations of infection in sheep other than abortion, which often occurs in the last 4 weeks of pregnancy. Full term lambs may be born dead, or alive but weak, often dying within the first 2 weeks of life. Mummified lambs, often one of a pair, may be seen. Goats are also susceptible to abortion following infection with toxoplasma. There is a live vaccine for use in sheep. Note however that it should not be handled by pregnant women or women of childbearing age, as it may interfere with normal foetal development.

Last reviewed: 25 August 2011