Toxoplasmosis - Sheep

• Sheep
  • Mostly asymptomatic
  • However, if a non-immune ewe is infected during pregnancy the consequences will be serious
    • Infection during the first trimester leads to resorption
  • Infection during the second trimester leads to foetal death and mummification
  • Infection during the last trimester leads to a weak or stillborn lamb
  • Aborted ewes show focal necrotic placentitis with white lesions in the cotyledons and foetal tissue
  • Diagnosis is confirmed by Giemsa and serology of the ewe's blood

Prevention:

• Clinical outbreaks of toxoplasmosis are sporadic
  • Immunity is acquired before tupping
  • Significant ill-effects are unlikely if immune ewes are infected during pregnancy
  • Not shed from sheep to sheep so predicting outbreaks is difficult
• Sheep
  • Toxovax vaccine
    • Live, avirulent strain of Toxoplasma
    • Does not form bradyzoites or tissue cysts
    • Killed by host immune system
    • Single dose given 6 weeks before tupping
    • Protects for 2 years
    • Immunity boosted by natural challenge
  • Medicated feed can be given daily during the main risk period
    • 14 weeks before lambing
  • The best method of protection is to prevent cats from contaminating the pasture, lambing sheds and feed stores