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Parasitology > 16. Protozoa (Toxo) > Flashcards

16. Protozoa (Toxo) Flashcards

1
Q

Is Toxo an intracellular parasite?

A

yes, obligate intracellular

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2
Q

does Toxo have high or low host specificity?

A

low - possibly infects any mammal

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3
Q

what tissues does Toxo infect?

A

almost all tissues

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4
Q

what is the definitive host of Toxo?

A

a cat, domestic or wild

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5
Q

how do cats become infected with Toxo?

A

by eating the oocysts or infected rodents or birds

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6
Q

what is the intermediate/reservoir host of Toxo?

A

most species of warm blooded animals

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7
Q

what are some ways that humans can become infected with toxo?

A

by ingesting a cyst, eating raw meat, transplacentally, or organ transplants

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8
Q

how does Toxo reproduce in the IH

A

asexually

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9
Q

how does Toxo reproduce asexually in the IH?

A
  • an ingested oocyst goes to the digestive tract, they are engulfed by macrophages
  • in the mac, the tachyzoites develop and travel to various parts of the body via the blood
  • once the immune system is triggered, the tachyzoites encyst into pseudocysts that contain bradyzoites
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10
Q

what is the infectious stage of Toxo?

A

all parasitic stages are infectious and can cause toxoplasmosis

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11
Q

how long following infection do cats shed oocysts?

A

for only 1-2 weeks following infection

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12
Q

when do oocysts become infective?

A

24-48 hours after remaining in feces

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13
Q

how long can oocysts remain viable in warm, moist soil?

A

years

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14
Q

what are the three forms of Toxo?

A
  1. oocysts
  2. Tachyzoites
  3. Bradyzoites (tissue cysts)
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15
Q

what does a sporulated oocyst contain?

A

2 sporocysts, each of which contain 4 sporozoites

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16
Q

what shape are the tachyzoites of Toxo?

A

crescent shaped

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17
Q

what is the parasite membrane called?

A

parasitophorous vacuolar membrane

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18
Q

what phase of infection is marked by the tachyzoites?

A

the acute phase

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19
Q

are tachyzoites the sexual or asexual form?

A

asexual

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20
Q

what kind of cells do tachyzoites invade?

A

all nucleated cells

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21
Q

tachyzoites invade nucleated cells and occur in _________.

A

in groups

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22
Q

at what stage in infection are tachyzoites rapidly growing?

A

in the early stage

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23
Q

what do tissue cysts contain?

A

slowly growing trophozoites known as bradyzoites

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24
Q

what is the appearance of a bradyzoite in body cells?

A

a circular mass

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25
Q

what do bradyzoites contain?

A

thousands of parasites

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26
Q

how long do brandyzoites remain in tissue?

A

for the life of the host

27
Q

what stage of infection is marked by bradyzoites?

A

the chronic phase

28
Q

when can reactivation of infection occur?

A

in immunocomprimized hosts

29
Q

what are bradyzoites resistant to?

A

low pH and digestive enzymes (for stomach passage)

30
Q

what do bradyzoites transform into?

A

tachyzoites

31
Q

what has to happen before bradyzoites transform into tachyzoites?

A

the protective cyst wall has to be dissolved

32
Q

where are bradyzoites released?

A

in the intestine

33
Q

what is needed for tachyzoite to bradyzoite conversion?

A
  • high pH
  • low pH
  • heat shock
  • mitochondrial inhibition
  • presence of nitric oxide
34
Q

what is needed for bradyzoite to tachyzoite conversion?

A
  • lack of nitric oxide
  • lack of IFN-γ
  • lack of TNF-α
  • lack of T-cells
  • lack of IL-12
35
Q

what are the two phases of the T. gondii life cycle?

A
  • the intestinal (or enteroepithelial)

- the extra-intestinal

36
Q

where does the intestinal phase occur?

A

only in cats

37
Q

what does the intestinal phase produce?

A

oocysts

38
Q

where does the extra-intestinal phase occur?

A

in all infected animals including cats

39
Q

what does the extra-intestinal phase produce?

A

tachyzoites and eventually bradyzoites

40
Q

what can occur if a kitten is infected?

A

rarely, acute infections can result in numerous intestinal lesions that kill kittens

41
Q

what are the clinical features of toxoplasmosis in humans, if there are symptoms?

A
  • mild fever
  • sore muscles
  • swollen glands and lymph nodes
42
Q

how are the clinical symptoms resolved in humans

A

clinical course is benign and self-limiting, usually resolves within a few months to a year

43
Q

who is most at risk for toxoplasmosis?

A

individuals who are immuno-compromised - patients suffering from HIV, organ transplant receivers, people on chemotherapy

44
Q

what is the most common cause of intra-cerebral mass lesions in patients with AIDS?

A

toxoplasmic encephalitis

45
Q

what do immunodeficient patients often have?

A

CNS disease, but many have retinochoroditis, or pneumonitis

46
Q

how many cases of congenital toxoplasmosis is estimated to occur per year in the US?

A

400-4000

47
Q

how many human deaths are associated with the clinical disease of Toxoplasmosis?

A

750, making it the 3rd most common lethal food poisoning

48
Q

what can congenital toxoplasmosis result in?

A

spontaneous abortion, a stillborn, or a child that is severely handicapped mentally or physically

49
Q

is the fetus at risk if it is not the mother’s first exposure to Toxo?

A

no, only if it is the first exposure

50
Q

are most cats actively shedding oocysts?

A

no

51
Q

about how many women that are infected actually pass the infection to the unborn baby?

A

30-40%

52
Q

what is the risk of passing the infection in the third trimester?

A

70%

53
Q

what is the risk of passing the infection in early pregnancy?

A

15%

54
Q

what are some common defects of congenital toxoplasmosis?

A
  • chorioretinitis (leading to blindness)
  • intre-cerebral calcification
  • hydrocephaly/microcephaly
55
Q

which is the least common defect of congenital toxo?

A

hydrocephalus, but it is the most dramatic

56
Q

what is the most common defect of toxo?

A

occular disease

57
Q

how is diagnosis of toxo done?

A
  • ELISA test for IgG and IgM - different titer results indicate different stages of infection. For exaxmple, acute vs. chronic
  • amniotic/spinal fluid isolation and culture of parasite
  • direct detection by microscopy
58
Q

what is the most reliable serological method for toxo diagnosis? how does it work?

A

Sabin-Feldman dye test - live tachyzoites are the antigen and are exposed to dilutions of the serum

59
Q

which medication are most commonly prescribed for toxoplasmosis infection?

A

pyrimethamine
sulfadiazine
clindamycin
spiramycin

60
Q

what is the use of pyrimethamine?

A

antimalarial medication

61
Q

what is the use of sulfadiazine?

A

antibiotic used in combination with pyramethamine to treat toxoplasmosis

62
Q

what is the use of clindamycin?

A

antibiotic used most often for people with HIV/AIDS

63
Q

what is the use of spiramycin?

A

antibiotic used most often for pregnant women to prevent the infection of their child

64
Q

what is the host manipulation that has been observed in rats infected with Toxoplasma gondii?

A

rats will no longer be prude about areas that have cat urine, instead they possibly even seek out those areas

Parasitology (27 decks)

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