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Microbiology > Toxoplasma > Flashcards

Toxoplasma Flashcards

0
Q

What kind of organism is T. gondii?

A

It is a crescent-shaped protozoan parasite.

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1
Q

What is the causative organism of toxoplasmosis?

A

Toxoplasma gondii

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2
Q

What animal plays a role in T. gondii transmission?

A

Cat.

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3
Q

What group of people are particularly at risk with regards to T.gondii?

A

Immunocompromised people. Infection is often fatal.

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4
Q

What is a cyst?

A

A cyst is a closed capsule or sac-like structure, typically filled with liquid, semisolid or gaseous material. Similar to a blister.

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5
Q

What is an oocyst?

A

A cyst containing a zygote formed by a parasite protozoan.

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6
Q

Outline the T.gondii life cycle.

A

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.

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7
Q

What happens once T.gondii enters a nucleated cell?

A

The organism multiplies until the cell lyses, releasing organisms to infect new cells.
A tissue cyst may be formed.

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8
Q

What happens as the immune response to T.gondii develops?

A

Acute phase of tissue destruction subsides.

Tissue cysts form.

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9
Q

Characteristics of tissue cysts?

A

They can remain inactive LATENT INFECTION but are viable for the entire life of the host.

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10
Q

What tissues do tissue cysts normally form in?

A

Brain.

Skeletal + cardiac muscle.

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11
Q

How may one contract T.gondii?

A 
Material contaminated with oocyst containing cat faeces.
Eating raw/uncooked meat from intermediate oocyst containing host.
Transplacental transmission (acute maternal infection).
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12
Q

How does T.gondii cause tissue pathology?

A

Organisms multiply in nucleated cells > death of cell with infection of contiguous cells > focus of necrosis that may calcify.

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13
Q

Which people are at particular risk of serious infection with T.gondii and why?

A

Immunocompromised.
Congenital infections.
*infection may progress to severe! potentially fatal,necrotising lesions in vital organs.

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14
Q

What vital organs can T.gondii cause necrotising lesions?

A

Brain.
Heart.
Lungs.

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15
Q

What is chorioretinitis and how is it related to T.gondii?

A

Reactivation of cysts deposited in or near the retina may cause chorioretinitis and may be recurrent.

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16
Q

What is chorioretinitis?

A

Inflammation of the choroid and retina of the eye.

17
Q

What are the three kinds of clinical presentations with regards to T.gondii infection?

A

Congenital infection.
Post-natal infection in immunocompetent person.
Primary infection or reactivation in immunocompromised person.

18
Q

What is the only way a woman can transmit T.gondii to her unborn child?

A

If she contracts a primary infection during pregnancy.

*immunity is protective

19
Q

How are incidence of congenital disease and timing of maternal infection related?

A

Maternal infection in 1st trimester lower incidence of disease than if in third trimester.

20
Q

Is it necessarily better for a pregnant woman to contract the disease in the 1st trimester?

A

No, as congenital disease is more severe if acquired during the first trimester.

21
Q

Proportion of infants born to mums who contract T.gondii during pregnancy?

A

1/3

22
Q

What does it mean when one says immunity to T.gondii is protective with regards to the foetus?

A

Immunity protects against subsequent congenital transmission.

23
Q

Other than congenital birth defects, what can happen to a foetus who contracts T.gondii?

A

Spontaneous abortion.
Prematurity.
Stillbirth.

24
Q

What clinical findings may one find in an infant infected with T.gondii?

A 
Chorioretinitis (bilateral)
Hydrocephaly
Lymphadenopathy
Hepatosplenomegaly
Blindness
25
Q

Clinical findings in a post-natal infection of an immunocompetent person?

A

Cervical lymphadenopathy.

Fever.

26
Q

How can T.gondii affect the eye in the immunocompetent individual?

A

Chorioretinitis (unilateral)

27
Q

What is T.gondii an infrequent cause of in the post-natal immunocompetent person?

A

Infectious mononucleosis syndrome

28
Q

Another name for infectious mononucleosis syndrome?

A

Glandular fever.

29
Q

Is T.gondii dangerous to the post-natal immunocompetent person?

A

Not normally. Illness is often benign and self-limiting.

Many people are asymptomatic.

30
Q

How dangerous is T.gondii to the immunocompromised person?

A

Primary infection or reactivation can cause serious infection in these individuals.

31
Q

What is the most common manifestation of T.gondii in immunocompromised people?

A

CNS involvement.

32
Q

What can T.gondii cause in immunocompromised individuals?

A

Meningitis.
Intracerebral lesions.
Myocarditis.
Pneumonitis.

33
Q

Three ways in which to diagnose a T.gondii infection?

.

A

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

34
Q

Comment on diagnosing congenital infection with T.gondii.

A

Measure IgG over several months to account for passively transferred antibody.
PCR on amniotic fluid can diagnose toxoplasmosis in-utero.

35
Q

Why is it often difficult to diagnose toxoplasmosis in pregnant women so that treatment can be started?

A

Because many of them are asymptomatic.

36
Q

How does one treat the immunocompetent individual infected with T.gondii?

A

Treatment unnecessary unless patient is a pregnant woman

*reduce incidence of fetal infection.

37
Q

Antibiotic used to treat immunocompromised and pregnant women?

A

Co-trimoxazole.

38
Q

Treatment in AIDS patients?

A

Lifelong co-trimoxazole suppressive therapy.

*tissue cysts never eradicated been with treatment

39
Q

How to prevent toxoplasmosis?

A 
Cook meat adequately.
Wash fruit and vegetables.
Freeze meat > kills cysts.
Wash hands.
Pregnant women should avoid contact with cat faeces.
40
Q

What is co-trimoxazole?

A

Trimethoprim and sulfamethoxazole.

Microbiology (18 decks)

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