Tissue cyst-forming coccidia

PARASITES PROTOZOA

Toxoplasma

• 1 major pathogenic species called Toxoplasma gondii

• Causes disease in a wide range of animal species including humans

• Important cause of abortion in sheep

• Zoonotic
  • Can cause abortion
  • Can cause congenitally aquired defects

• Forms a sporulated oocyst which is only 10μm
  • Contains 2 sporocysts with 4 sporozoites

• Transmission through ingesting the intermediate host or via the faecal-oral route

Life Cycle

• Complex

• Usually indirect

• Gametogeny (sexual stage) is host specific for felids

• Any warm blooded animal can act as a facultative intermediate host
  • Asexual reproduction occurs in the intermediate host forming tissue cysts
  • Intermediate host swallows sporulated oocysts or tissue cysts
  • Can be transferred between intermediate hosts by carnivorism

Toxoplasma can cause acute interstitial pancreatitis in systemic toxoplasmosis

• T. gondii in pneumonia
• Toxoplasma gondii, Sarcocystis and Neospora caninum in myositis

Sarcocystis

• Most infections are asymptomatic

• Heavy infections are causes of chronic wasting in large animals, hide sondemnation and downgrading of carcasses

• Sarcocystis should be differentiated from other tissue-cyst forming coccidia

• There are many species of Sarcocystis

• Sporulated oocyst has 2 sporocysts containing 4 sporozoites
  • Naked oocyst usually seen in faeces as the oocyst wall is very delicate

• Indirect life cycle

• Life cycle alternates between the final and the obligatory intermediate host

• Only one final and one intermediate host

Neospora

• 2 main species
  • Neospora caninum in the dog
  • Neospora hughesi in the horse

• Sporulated oocysts measuring just 10μm

• Oocyst contains 2 sporocysts with 4 sporozoites

• Life cycle similar to Toxoplasma gondii

• Limited range of warm-blooded intermediate hosts
  • Asexual reproduction occurs in intermediate host forming tissue cysts

• Host range of sexual stage is unknown for N.caninum
  • Intermediate host for N.hughesi is the horse, but the definitive host is unknown

• Route of transmission not fully understood