Toxoplasmosis
Toxoplasmosis is an infection caused by the parasite Toxoplasma gondii (T. gondii). It occurs worldwide and affects a wide range of warm-blooded animals, including humans.
Key facts
Why it matters
Toxoplasmosis is one of the most common causes of abortion in sheep and is responsible for reproductive and production losses in sheep. Toxoplasmosis can also affect other livestock such as goats and pigs, as well as humans. In sheep, toxoplasmosis causes around a quarter of diagnosed abortions each year.
Abortions and barren ewes can cause many issues for farmers. Farm profitability can be impacted, as a lower lamb crop means fewer lambs to sell or to choose replacements from.
Toxoplasmosis is an infection caused by the parasite Toxoplasma gondii (T. gondii). It occurs worldwide and affects a wide range of warm blooded animals, including humans. Most people infected with toxoplasmosis do not develop symptoms, but the infection can cause serious health problems in certain groups, particularly during pregnancy or in people with weakened immune systems.
Transmission
Cats: Cats can shed millions of tough-shelled T. gondii oocysts (eggs) in their faeces. The oocysts are very durable and can survive for long periods of time in the environment, especially in temperate, moist conditions.
Feed contamination and water: Cat faeces containing infective oocysts can contaminate feed, fodder, bedding, and water sources on farm.
People can become infected with T. gondii by either consuming the eggs of the parasite, through cysts in meat from animals infected with T. gondii, or as a baby in the womb.
Cats are the definitive host of T. gondii, this means the parasite can only complete its life cycle in the gut of a cat. Cats become infected by eating infected rodents or birds while hunting. The parasite eggs (oocysts) are passed in the cat’s faeces.
People become infected when they ingest the eggs. This can happen by:
- Cleaning a cat’s litter tray and not washing hands afterwards
- Ingesting contaminated soil while gardening
- Eating unwashed fruit or vegetables that have contaminated soil on them
- Drinking contaminated water
People can also become infected via food and drink: eating contaminated undercooked meat or freezing before cooking will kill the parasite, eating cured meat (curing does not kill the parasite), eating undercooked shellfish, or drinking raw goat’s milk. Infection can also pass from a pregnant woman to her unborn child (congenital transmission).
Clinical Signs
If ewes become infected with Toxoplasma for the first time during pregnancy, the consequences for the developing foetus can be severe. Severity depends on the timing of infection, with earlier infection resulting in a more severe outcome.
- Early pregnancy: infection is likely to result in resorption of the foetus, with the ewe returning to service or remaining empty
- Mid-pregnancy: foetuses are often mummified or aborted a few days before the expected lambing date
- Late pregnancy: infection may not be fatal to the foetus, and lambs that survive are born live but may be weak, many dying shortly after birth
In non-pregnant or male sheep, infection is usually not noticed. Some sheep may have a mild temperature or lack of appetite for a short time.
Healthy people: If you are otherwise healthy, it is unlikely that you will know you have become infected. Most healthy people experience no symptoms; some experience mild flu-like symptoms such as fatigue, muscular aches, enlarged lymph nodes, headache, or high temperature.
People with weakened immune systems: More serious symptoms can occur in people with weakened immune systems, such as those with HIV infection or undergoing chemotherapy. If infected before becoming immunocompromised, the parasite can reactivate and cause disease.
During pregnancy: If you are already infected before becoming pregnant, there is no risk to your unborn child. If infection occurs shortly before or during early pregnancy, it can be passed to the unborn child. The earlier in pregnancy infection occurs, the more severe the outcome, potentially miscarriage, stillbirth, or a child born with an unusually large or small head. Babies born with the infection may show no symptoms at birth but can go on to develop cognitive disabilities, vision or hearing problems, or seizures.
Other countries: In some parts of the world the strain of T. gondii is more harmful than the types usually found in the UK and Europe, and can cause eye disease with damage to the retina and vision loss.
Diagnosis
What farmers might notice
You cannot diagnose toxoplasmosis from clinical signs alone, but you may notice placentas with small white, chalky areas in the cotyledons (buttons). These are caused by necrosis and calcification in areas of the placenta due to damage from the parasite multiplying.
Lab confirmation
Confirmation must be done by a vet. Collect freshly aborted lambs and placentas, if possible into separate bags, and speak with your vet to arrange testing.
When to call a vet
If more than 2% of your ewes are barren or abort in the lambing season, it’s advisable to call your vet. They can screen blood samples from a small group of ewes to determine whether toxoplasmosis, or another infectious disease such as enzootic abortion (EAE), has been involved.
Prevention and Control
There is no way to cure sheep once infected with T. gondii, but it’s worth keeping sheep that have aborted due to toxoplasmosis, as they are now immune and will not abort future pregnancies due to Toxoplasma.
Vaccination: The gold standard for prevention and control is vaccination, though difficulties in obtaining the vaccine can make this hard. The vaccine available in the UK provides life-long immunity (only one vaccination per ewe needed), so each year it’s only necessary to vaccinate replacements. Non-pregnant females should be vaccinated up to three weeks prior to tupping. It is a live vaccine; pregnant women and immune-compromised people should not administer it.
Feed storage and cat management: Keep feed bins and stores covered to prevent cats defecating in them, and keep cats away from fodder and bedding. Cats are the definitive host of the parasite, and older, neutered cats are preferable to kittens for rodent control on farm.
Biosecurity: Although T. gondii cannot pass from one sheep to another, isolate any aborted ewes and dispose of the placenta, dead lambs, and soiled bedding appropriately. Disinfect the lambing pen. At the point of abortion the cause cannot be determined, so each case should be treated as though it could spread throughout the flock.
Am I at risk?
Toxoplasmosis does not usually cause serious illness, and most people show no signs of infection. If you are pregnant or have a weakened immune system, you are at greater risk of more severe infection than if you were healthy. In pregnancy, it is not the pregnant woman at risk but the unborn child. Speak to your GP if you’re worried about your risk.
Timeline
Downloads & links
Related Resources
Video
Tackling Toxoplasmosis
Learn more more about Toxoplasmosis, including how to tackle the disease, in this fun animation
Key resource
Factsheets
Control of Toxoplasma Abortion in Sheep
Published 31/05/2019Who's involved
Our Experts
Frequently asked questions
FAQ
A common parasitic infection caused by the protozoan parasite Toxoplasma gondii. Many people have no symptoms when they become infected, but it can cause serious illness during pregnancy or in people with weakened immune systems.
- People can become infected by:
- Eating undercooked or raw meat
- Handling contaminated soil (e.g. gardening)
- Eating unwashed fruit or vegetables
- Contact with cat faeces (for example, cleaning litter trays)
- Infection passed from mother to unborn baby
Many people have been exposed to Toxoplasma gondii at some point in their lives, symptoms are often mild so people are not aware that they have been exposed. Studies looking at blood samples estimate that around 18% of the population have been exposed to Toxoplasma (Eurosurveillance | Systematic review and modelling of Toxoplasma gondii seroprevalence in humans, Europe, 2000 to 2021). The seroprevalence (number of people in a population who test positive for a specific disease) in the UK and Northern Europe is much lower than in other European countries where the seroprevalence is around 40 – 50%.
Most healthy people have no symptoms. When symptoms do occur, they may include:
- Mild flu-like illness
- Swollen lymph nodes
- Muscle aches
- Fatigue
More severe illness can occur in pregnancy or in people with weakened immune systems. In other part of the world, such as South America, Toxoplasma gondii can cause more serious illness and can affect the eyes.
If you have severe symptoms such as blurred vison then you should contact NHS24 or your GP for advice.
For most healthy people, toxoplasmosis is not dangerous. However, it can cause serious health problems:
- During pregnancy, it can harm the unborn baby
- In people with weakened immune systems, it can affect the brain, eyes, or other organs
Yes, but the risk is often misunderstood. Cats can shed the parasite in their faeces for a short period, usually after first becoming infected as a young kitten. Good hygiene and simple precautions greatly reduce the risk. It is important to understand that you cannot become infected with Toxoplasmosis from touching or stroking a cat or having a cat in your house.
You can reduce your risk by:
- Cooking meat thoroughly (especially lamb, pork and venison)
- Avoiding eating raw/undercooked meat or cured meats
- Washing hands after handling raw meat or soil
- Washing fruit and vegetables
- Wearing gloves when gardening
- Avoiding handling cat litter where possible, especially during pregnancy. If unavoidable then wear gloves and washing your hands afterwards
If a woman becomes infected for the first time during pregnancy, the infection can be passed to the unborn baby and may cause serious health problems. If you are infected before you get pregnant then there is no risk to your baby. If you are infected in early pregnancy, it can increase your risk of miscarriage and stillbirth, later in pregnancy becoming infected may cause serious health problems for your baby.
The chances of becoming infected for the first time during pregnancy is low.
No. Pregnant women do not need to avoid cats, but they should avoid handling cat litter and take extra hygiene precautions. You cannot become infected with Toxoplasmosis from touching or stroking a cat or having a cat in your house.
Routine screening for toxoplasmosis is not currently offered as part of NHS antenatal care in the UK. Testing may be carried out if there is a specific clinical concern. If you think you have been exposed to Toxoplasmosis during pregnancy you should speak to your GP or midwife for advice.
