Toxoplasma gondii Flashcards
Toxoplasma gondii is the main cause of?
Abortion in sheep
What are the end results of asexual and sexual reproduction?
Asexual = multiplication of parasite numbers
Sexual reproduction = recombination of genetic material
What are some characteristics of an apical complex?
- involved in host cell invasion
- single celled
- distinguishable by the conoid at the end of the parasite
- contains: dense cell granules, microneme, rhoptry
Name the 3 stages of growth of the toxoplasma gondii parasite
- Tachyzoite
- Bradyzoite
- Oocyst
Describe a tachyzoite
- Intracellular
- Rapidly dividing
- Crescent shaped - 2-6um
Describe a bradyziote
- Within a bradyzoite cyst
- Neural or muscle tissue
- Slow growing
- Persistant
Describe an oocyst
- Unsporulated oocyst passed in faeces
- 12um
- Sporulated oocyst => two sporocysts => 4 sporozoites
What is the definitive host of Toxoplasma gondii?
Cat
How do cats become infected with Toxoplasma?
Ingesting bradyzoite cysts in the tissues of prey
Describe the life cycle of Toxoplasma inside the definitive host
- sexual cycle occurs in the small intestine
- unsporulated oocysts shed in faeces
How does infection of the intermediate host with toxoplasma occur?
- Oocysts sporulate to two sporocysts and then to four sporozoites
- these contaminate the environment before being ingested by any warm blooded mammal
Describe the life cycle of Toxoplasma inside the intermediate host
- sporozoite’s released and travel across the gut wall
- develop into tachyzoites which replicate rapidly
- differentiate into bradyzoites which form cysts
Describe toxoplasmosis in sheep
- Transmission by ingestion of infective sporulated oocysts
- Oocysts from cats that contaminate the pasture
- No direct sheep-sheep transmission
How many oocysts can be out put from a cat?
more than 10,000
How many oocysts does it take to cause abortion in a sheep?
1000
Do sheep show clinical signs of a toxoplasma infection?
No
What are the clinical manifestations of toxoplasma in a pregnant sheep
- Still births
- Abortions
- Mummifications
- White, discrete lesions on cotyledons
What are the consequences for the foetus and mother if toxoplasma infection occurs in the first 40 days of pregnancy?
Foetal death and reabsorption
Infertile ewe
What are the consequences for the foetus and mother if toxoplasma infection occurs between day 40 and 110 of pregnancy?
Parasite becomes established in the placenta and foetus causing abortion
What are the consequences for the foetus and mother if toxoplasma infection occurs from day 110 of pregnancy?
Parasite becomes established damaging the placenta and cotyledons
Congenital infection - brain damage and birth defects
Describe how you would use serology to diagnose ovine toxoplasmosis
Antibody detection in serum or foetal fluids
- Immunofluorescence antibody test (IFAT)
- Agglutination tests
- Dye test
Describe how you would use histology to diagnose ovine toxoplasmosis
- Cotyledons
- Brain tissue
- Non-suppurative inflammation: Infiltration of leukocytes, macrophages and monocytes which gives an indication of protozoal infection
What management techniques can be implemented to control Toxoplasma-associated abortion in sheep?
- Infection with Toxoplasma induces strong immunity
- Introduce new stock well before tupping
- Protect feedstuffs from access by cats
How can you treat toxoplasma in sheep?
- No way of treating infection
- Dispose dead lambs and infected placentas
- Disinfect contaminated pens
Is there a vaccine available for Toxoplasma gondii?
Yes - Toxovax - vaccine to protect sheep against Toxoplasma abortion
What is the main source of Toxoplasma infection for ewe
Oocysts shed by cats, contaminating pasture or feed.
What advice would you give to a pregnant woman wanting to
(a) vaccinate ewes with Toxovax and
(b) around lambing?
(a) don’t administer the vaccine as there is a risk of accidental self-injection that could harm her baby
(b) avoid the lambing shed as a small risk of contracting infection through contaminated foetuses/placentae at lambing.
