Toxoplasmosis - Sheep

Description

Toxoplasmosis is the disease caused by Toxoplasma gondii, a protozoan parasite. Although the definitive host is the cat, T. gondii can infect all mammals including man and is a significant cause of abortion in sheep and goats. Toxoplasmosis does not seem to cause disease in cattle.

Life Cycle

• 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

Diagnosis

Clinical Signs

• 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

Pathology

Aborted ewes show focal necrotic placentitis with white lesions in the cotyledons and foetal tissue

Treatment

• 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

References

1. Buxton, D (1990) Ovine toxoplasmosis: a review. Journal of the Royal Society of Medicine, 83, 509-511.
2. Innes, E A et al (2009) Ovine toxoplasmosis. Parastiology, 136, 1887–1894.
3. Buxton, D et all (2007) Toxoplasma gondii and ovine toxoplasmosis: New aspects of an old story. Veterinary Parasitology, 147, 25-28.
4. Dubey, J P (2009) Toxoplasmosis in sheep — The last 20 years. Veterinary Parasitology, 163, 1-14.