Toxoplasma Flashcards
What are the different protozoa in sheep and cattle?
Toxoplasma gondii- abortion in sheep- zoonotic
Neospora caninum- abortion in cattle
Babesia spp- acuta, fatal tickborne in cattle
Cryptosporidium- diarrhoea in young ruminants- zoonotic
Eimeria- diarrhoea in lambs and calves
Sarcocystis spp
What are Apicomplexa?
A phylum which contains a large group of protoza, mostly intracellular with both sexual and asexual reproduction, locomotion by gliding
What protozoa are included in apicomplexa?
Plasmodium, Babesia, Eimeria, Toxoplasma, Neospora
How can a apicomplexa be identified generally?
Characteristic apical complex- involved in host cell invasion
Describe the structure of an apicomplexan zoite using the image below
What can toxoplasma gondii infect?
Can infect any warm blooded animals- birds and mammals
Second most important cause of abortion in sheep in Britain
What are the three life cycle stages of toxoplasma gondii?
Tachyzoite
Bradyzoite
Oocyst
What happens in each of the different life cycle stages of toxoplasma gondii?
Tachyzoite- intracellular, rapidly dividing, crescent shaped, 2x6um
Bradyzoite- found within bradyzoite cyst in neural or muscle tissue, slow growing and persistent
Oocyst- found in cat faeces, unsporulated when passed, sporulated oocyst contains two sporocysts each with four sporozoites- 12um in diameter
Which picture shows which stage of the toxoplasma gondiis life cycle?
What is the definitive host of toxoplasma gondii?
Cats is the definitive host, infected by ingesting bradyzoite cysts in tissues of prey
Describe the life cycle of toxoplasma gondii
Cats infected by ingesting bradyzoite cysts in tissues of prey
Sexual cycle in the SI, unsporulated oocysts shed in faeces. 12um in diameter.
24-48 hours the oocyst sporolates to contain two sporocysts each containing four sporozoites and is eaten by a warm blooded animal
In intermediate host (rodents/birds), sporozoites released, cross gut wall and develop into tachyzoited which replicate rapidly, differentiate into bradyzotes and form cysts
How is toxoplasmosis transmitted to sheep?
Transmission by ingestion of infective sporulated oocysts
Oocysts from cats contaminate the pasture
No direct sheep to sheep transmission
What are the clinical signs of toxoplasma infection in cats?
No clinical signs
How many oocysts are needed to cause abortion in sheep and how many oocysts do cats shed?
10^3 oocysts cause abortion in sheep
10^8 oocysts shed from Cats
So 100 cats could produce enough oocysts to cause abortions in all UK sheep
What are the clinical manifestations of sheep with toxoplasmosis?
Still births
Abortions
Mummification
White, descrite lesions on cotyledons ‘strawberries’
How does the outcome of toxoplasmasmosis vary when the time of infection occurs?
If infected whilst not pregnant there is a strong immune response
If infected before 40 days of pregnancy the sheep is likely do be infertile/barren
If infected before 110 days of pregnancy the sheep will abort
If after 110 days of pregnancy the lambs might be born live but will have a congenital infection
How is ovine toxoplasmosis diagnosed?
Serology- antibody detection in serum or foetal fluids- dye tests (humans gold standard), IFAT, agglutination tests (LAT, DAT)
Histology- cotyledons, brain tissue, typical non-supprative inflammation
How is toxoplasma abortion in sheep controlled?
Managment- infection with toxoplasma induces strong immunity, introduce new stock well before tupping
Vaccination
How does the toxoplasmosis vaccine work?
Promotes cell mediated immunity against altered live parasites (live attenuated)
Based on the S48 strain- cannot form bradyzoite cysts
Risk of accidental infection to humans
