Toxoplasma Flashcards
What kind of organism is T. gondii?
It is a crescent-shaped protozoan parasite.
What is the causative organism of toxoplasmosis?
Toxoplasma gondii
What animal plays a role in T. gondii transmission?
Cat.
What group of people are particularly at risk with regards to T.gondii?
Immunocompromised people. Infection is often fatal.
What is a cyst?
A cyst is a closed capsule or sac-like structure, typically filled with liquid, semisolid or gaseous material. Similar to a blister.
What is an oocyst?
A cyst containing a zygote formed by a parasite protozoan.
Outline the T.gondii life cycle.
Oocysts excreted in cat faeces > oocyts ingested by man/other animals > enzymes release viable protozoans > organisms penetrate gut wall > enter bloodstream > organisms enter nucleated cells and multiply
*cycle completed when cat eats infected host. Sexual cycle in cats intestines.
What happens once T.gondii enters a nucleated cell?
The organism multiplies until the cell lyses, releasing organisms to infect new cells.
A tissue cyst may be formed.
What happens as the immune response to T.gondii develops?
Acute phase of tissue destruction subsides.
Tissue cysts form.
Characteristics of tissue cysts?
They can remain inactive LATENT INFECTION but are viable for the entire life of the host.
What tissues do tissue cysts normally form in?
Brain.
Skeletal + cardiac muscle.
How may one contract T.gondii?
Material contaminated with oocyst containing cat faeces. Eating raw/uncooked meat from intermediate oocyst containing host. Transplacental transmission (acute maternal infection).
How does T.gondii cause tissue pathology?
Organisms multiply in nucleated cells > death of cell with infection of contiguous cells > focus of necrosis that may calcify.
Which people are at particular risk of serious infection with T.gondii and why?
Immunocompromised.
Congenital infections.
*infection may progress to severe! potentially fatal,necrotising lesions in vital organs.
What vital organs can T.gondii cause necrotising lesions?
Brain.
Heart.
Lungs.
What is chorioretinitis and how is it related to T.gondii?
Reactivation of cysts deposited in or near the retina may cause chorioretinitis and may be recurrent.
What is chorioretinitis?
Inflammation of the choroid and retina of the eye.
What are the three kinds of clinical presentations with regards to T.gondii infection?
Congenital infection.
Post-natal infection in immunocompetent person.
Primary infection or reactivation in immunocompromised person.
What is the only way a woman can transmit T.gondii to her unborn child?
If she contracts a primary infection during pregnancy.
*immunity is protective
How are incidence of congenital disease and timing of maternal infection related?
Maternal infection in 1st trimester lower incidence of disease than if in third trimester.
Is it necessarily better for a pregnant woman to contract the disease in the 1st trimester?
No, as congenital disease is more severe if acquired during the first trimester.
Proportion of infants born to mums who contract T.gondii during pregnancy?
1/3
What does it mean when one says immunity to T.gondii is protective with regards to the foetus?
Immunity protects against subsequent congenital transmission.
Other than congenital birth defects, what can happen to a foetus who contracts T.gondii?
Spontaneous abortion.
Prematurity.
Stillbirth.
