16. Protozoa (Toxo)

Question 1

Is Toxo an intracellular parasite?

Answer 1

yes, obligate intracellular

Question 2

does Toxo have high or low host specificity?

Answer 2

low - possibly infects any mammal

Question 3

what tissues does Toxo infect?

Answer 3

almost all tissues

Question 4

what is the definitive host of Toxo?

Answer 4

a cat, domestic or wild

Question 5

how do cats become infected with Toxo?

Answer 5

by eating the oocysts or infected rodents or birds

Question 6

what is the intermediate/reservoir host of Toxo?

Answer 6

most species of warm blooded animals

Question 7

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

Answer 7

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

Question 8

how does Toxo reproduce in the IH

Answer 8

asexually

Question 9

how does Toxo reproduce asexually in the IH?

Answer 9

• 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

Question 10

what is the infectious stage of Toxo?

Answer 10

all parasitic stages are infectious and can cause toxoplasmosis

Question 11

how long following infection do cats shed oocysts?

Answer 11

for only 1-2 weeks following infection

Question 12

when do oocysts become infective?

Answer 12

24-48 hours after remaining in feces

Question 13

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

Answer 13

years

Question 14

what are the three forms of Toxo?

Answer 14

1. oocysts
2. Tachyzoites
3. Bradyzoites (tissue cysts)

Question 15

what does a sporulated oocyst contain?

Answer 15

2 sporocysts, each of which contain 4 sporozoites

Question 16

what shape are the tachyzoites of Toxo?

Answer 16

crescent shaped

Question 17

what is the parasite membrane called?

Answer 17

parasitophorous vacuolar membrane

Question 18

what phase of infection is marked by the tachyzoites?

Answer 18

the acute phase

Question 19

are tachyzoites the sexual or asexual form?

Answer 19

asexual

Question 20

what kind of cells do tachyzoites invade?

Answer 20

all nucleated cells

Question 21

tachyzoites invade nucleated cells and occur in _________.

Answer 21

in groups

Question 22

at what stage in infection are tachyzoites rapidly growing?

Answer 22

in the early stage

Question 23

what do tissue cysts contain?

Answer 23

slowly growing trophozoites known as bradyzoites

Question 24

what is the appearance of a bradyzoite in body cells?

Answer 24

a circular mass

Question 25

what do bradyzoites contain?

Answer 25

thousands of parasites

Question 26

how long do brandyzoites remain in tissue?

Answer 26

for the life of the host

Question 27

what stage of infection is marked by bradyzoites?

Answer 27

the chronic phase

Question 28

when can reactivation of infection occur?

Answer 28

in immunocomprimized hosts

Question 29

what are bradyzoites resistant to?

Answer 29

low pH and digestive enzymes (for stomach passage)

Question 30

what do bradyzoites transform into?

Answer 30

tachyzoites

Question 31

what has to happen before bradyzoites transform into tachyzoites?

Answer 31

the protective cyst wall has to be dissolved

Question 32

where are bradyzoites released?

Answer 32

in the intestine

Question 33

what is needed for tachyzoite to bradyzoite conversion?

Answer 33

- high pH - low pH - heat shock - mitochondrial inhibition - presence of nitric oxide

Question 34

what is needed for bradyzoite to tachyzoite conversion?

Answer 34

- lack of nitric oxide - lack of IFN-γ - lack of TNF-α - lack of T-cells - lack of IL-12

Question 35

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

Answer 35

- the intestinal (or enteroepithelial) | - the extra-intestinal

Question 36

where does the intestinal phase occur?

Answer 36

only in cats

Question 37

what does the intestinal phase produce?

Answer 37

oocysts

Question 38

where does the extra-intestinal phase occur?

Answer 38

in all infected animals including cats

Question 39

what does the extra-intestinal phase produce?

Answer 39

tachyzoites and eventually bradyzoites

Question 40

what can occur if a kitten is infected?

Answer 40

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

Question 41

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

Answer 41

- mild fever - sore muscles - swollen glands and lymph nodes

Question 42

how are the clinical symptoms resolved in humans

Answer 42

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

Question 43

who is most at risk for toxoplasmosis?

Answer 43

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

Question 44

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

Answer 44

toxoplasmic encephalitis

Question 45

what do immunodeficient patients often have?

Answer 45

CNS disease, but many have retinochoroditis, or pneumonitis

Question 46

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

Answer 46

400-4000

Question 47

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

Answer 47

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

Question 48

what can congenital toxoplasmosis result in?

Answer 48

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

Question 49

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

Answer 49

no, only if it is the first exposure

Question 50

are most cats actively shedding oocysts?

Answer 50

no

Question 51

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

Answer 51

30-40%

Question 52

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

Answer 52

70%

Question 53

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

Answer 53

15%

Question 54

what are some common defects of congenital toxoplasmosis?

Answer 54

- chorioretinitis (leading to blindness) - intre-cerebral calcification - hydrocephaly/microcephaly

Question 55

which is the least common defect of congenital toxo?

Answer 55

hydrocephalus, but it is the most dramatic

Question 56

what is the most common defect of toxo?

Answer 56

occular disease

Question 57

how is diagnosis of toxo done?

Answer 57

- 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

Question 58

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

Answer 58

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

Question 59

which medication are most commonly prescribed for toxoplasmosis infection?

Answer 59

pyrimethamine sulfadiazine clindamycin spiramycin

Question 60

what is the use of pyrimethamine?

Answer 60

antimalarial medication

Question 61

what is the use of sulfadiazine?

Answer 61

antibiotic used in combination with pyramethamine to treat toxoplasmosis

Question 62

what is the use of clindamycin?

Answer 62

antibiotic used most often for people with HIV/AIDS

Question 63

what is the use of spiramycin?

Answer 63

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

Question 64

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

Answer 64

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