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.
What clinical findings may one find in an infant infected with T.gondii?
Chorioretinitis (bilateral) Hydrocephaly Lymphadenopathy Hepatosplenomegaly Blindness
Clinical findings in a post-natal infection of an immunocompetent person?
Cervical lymphadenopathy.
Fever.
How can T.gondii affect the eye in the immunocompetent individual?
Chorioretinitis (unilateral)
What is T.gondii an infrequent cause of in the post-natal immunocompetent person?
Infectious mononucleosis syndrome
Another name for infectious mononucleosis syndrome?
Glandular fever.
Is T.gondii dangerous to the post-natal immunocompetent person?
Not normally. Illness is often benign and self-limiting.
Many people are asymptomatic.
How dangerous is T.gondii to the immunocompromised person?
Primary infection or reactivation can cause serious infection in these individuals.
What is the most common manifestation of T.gondii in immunocompromised people?
CNS involvement.
What can T.gondii cause in immunocompromised individuals?
Meningitis.
Intracerebral lesions.
Myocarditis.
Pneumonitis.
Three ways in which to diagnose a T.gondii infection?
.
Serology:
- testing for IgG and IgM antibodies
Histology:
- tissue cysts can be seen in cross sections
- lymph nodes have a characteristic appearance
Culture:
- hazardous therefore seldom performed
Comment on diagnosing congenital infection with T.gondii.
Measure IgG over several months to account for passively transferred antibody.
PCR on amniotic fluid can diagnose toxoplasmosis in-utero.
Why is it often difficult to diagnose toxoplasmosis in pregnant women so that treatment can be started?
Because many of them are asymptomatic.
How does one treat the immunocompetent individual infected with T.gondii?
Treatment unnecessary unless patient is a pregnant woman
*reduce incidence of fetal infection.
Antibiotic used to treat immunocompromised and pregnant women?
Co-trimoxazole.
Treatment in AIDS patients?
Lifelong co-trimoxazole suppressive therapy.
*tissue cysts never eradicated been with treatment
How to prevent toxoplasmosis?
Cook meat adequately. Wash fruit and vegetables. Freeze meat > kills cysts. Wash hands. Pregnant women should avoid contact with cat faeces.
What is co-trimoxazole?
Trimethoprim and sulfamethoxazole.
