printStock Journal Technical Column: October 2026
Author: Colin Trengove, Pro Ag Consulting
Toxoplasmosis is an important cause of reproductive losses in sheep in South Australia. With estimates suggesting that toxoplasmosis costs the South Australian sheep industry approximately $70 million annually.
Toxoplasmosis, unlike many other infectious diseases, it is spread primarily through contamination of the environment by infected cats. Surveys in SA, suggest that interactions between cats and sheep are more common than many producers realise, increasing the potential for disease transmission. Toxoplasmosis is also a zoonotic disease, meaning it can also infect humans. Good hygiene and farm biosecurity are therefore essential to protect both livestock and people.
How is toxoplasmosis spread?
Toxoplasmosis is caused by the parasite Toxoplasma gondii. Cats play a central role in the parasite's lifecycle. They commonly become infected when they hunt and consume infected prey, such as rodents, birds and other small mammals.
Following infection, cats can shed large numbers of parasite eggs, known as oocysts, in their faeces. These oocysts contaminate the environment and can subsequently be ingested by sheep through contaminated feed, pasture or water. The parasite can persist in wildlife populations, helping maintain the cycle of infection.
How does toxoplasmosis affect sheep?
Toxoplasmosis can cause substantial reproductive losses, particularly when previously uninfected ewes become infected during pregnancy.
The outcome depends largely on the stage of pregnancy when infection occurs:
- Early pregnancy: Infection may result in embryonic death and resorption, reducing the number of lambs born.
- Mid-pregnancy: Infection can cause abortion or the birth of dead or weak lambs.
- Later pregnancy: Infection may also result in weak or stillborn lambs, although outcomes vary.
These reproductive losses can significantly reduce lamb marking percentages and farm profitability.
Diagnosis
Toxoplasmosis should be considered when investigating abortions, stillbirths or unexpectedly low lamb marking percentages.
Characteristic findings can include small, white, chalky lesions, approximately 2 mm in diameter, on the placenta. However, these lesions alone are not sufficient for a definitive diagnosis.
Veterinary examination and laboratory testing of appropriate placental and foetal tissues may be required to confirm infection and distinguish toxoplasmosis from other causes of reproductive loss.
Recommendations for reducing toxoplasmosis
An integrated management approach is needed to reduce toxoplasmosis. Feral cat control is a key component, supported by practical changes to farm management and improved biosecurity.
1. Feral cat control
Reducing feral cat numbers can help limit environmental contamination with Toxoplasma gondii. Control options include trapping, shooting, containment fencing and approved baiting programs, including the use of 1080 where authorised.
2. Improve farm biosecurity
Producers can reduce the risk of infection by limiting opportunities for cats to contaminate livestock feed and water.
Practical measures include:
- Preventing cats from accessing stored feed, particularly hay, grain and supplementary feed.
- Restricting cat access to water supplies wherever possible.
- Promptly and appropriately disposing of sheep carcasses and offal to reduce food sources for feral cats.
- Maintaining good hygiene when handling potentially contaminated materials.
These measures can help protect livestock while also reducing the risk of human exposure.
3. Vaccination
Live, attenuated vaccines have been used successfully in New Zealand, providing protective immunity and improving lambing outcomes. However, these vaccines are not currently suitable for use in Australia because of biosecurity concerns and practical difficulties associated with their use under Australian climatic conditions.
Research is underway to develop a killed vaccine that may be more suitable for Australian conditions. If successful, vaccination could provide an additional tool for reducing reproductive losses associated with toxoplasmosis.
In summary, Toxoplasmosis is an important but often overlooked cause of lamb losses. Reducing feral cat numbers, protecting feed and water supplies, and maintaining good farm biosecurity are the key management strategies currently available to producers.
Improved diagnostic awareness and the potential development of a suitable vaccine may provide further opportunities to reduce the disease's impact on lamb survival and farm profitability.