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Control of Toxoplasma Abortion in Sheep

  • Toxoplasma gondii is the most successful parasite worldwide, capable of infecting all warm blooded animals, including humans, and causes the disease toxoplasmosis.
  • The cat is the definitive host of the parasite and young kittens ofter get infected when they fo out hunting for the first time.  The parasite develops in the gut of the cat and Toxoplasma oocysts (eggs) are shed in faeces into the enviroment.
  • Toxoplasma oocysts sporulate, i.e. they come infectious, outside the host and they have a tougher outer shell enabling them to survive in the environment in moist temperate conditions for serveral years.
  • Sheep may become infected by ingesting infective oocysts on pasture or in contaminated feed and water.
  • If the parasite infects the pregnant animal for the first time, Toxoplasma can cause disease in the placenta and the developing foetus.
  • Infection early in pregnancy may result in abortion, whereas infection later in pregnancy may cause still birth, a mummified foetus or the birth of a live infected and weak lamb.
  • Following infection, sheep develop immunity against the parasite which will protect them against disease in a subsequent pregnancy.
  • There is an effective vaccine to prevent congenital toxoplasmosis in sheep (disease caused by the parasite passing from the dam to the foetus)..
  • Once animals or people become infected with Toxoplasma it is thought that they will remain infected for life with the parasite remaining dormant within tissue cysts.
  • Toxoplasma may also be transmitted to humans from the ingestion of oocysts or from eating undercooked meat containing parasite tissue cysts.
  • Pregnant women and immuno-compromised individuals are major risk groups and should also avoid contact with ewes at lambing time.