Toxoplasma

Question 1

Which species belong to the toxoplasma species?

Answer 1

toxoplasma gondii is the only species in the genus

Question 2

Where is this parasite found?

Answer 2

in cities around the world. obligate intracellular parasite that has a low specificity and will probably infect any mammal. also found in birds. can infect most tissues of the body

Question 3

What are the effects of toxoplasmosis?

Answer 3

asymptomatic in healthy adults- will form cysts in immunologically privileged sites
can cause the death of the fetus

Question 4

Why does increased infection occur in older individuals?

Answer 4

bope, but it does

Question 5

Why is the frequency of infection higher in Central America?

Answer 5

because their is a greater number of stray cats and the climate favours oocysts (esp. when in soil).
lower altitudes also favour the disease

Question 6

What dietary habit increases the frequency of toxoplasmosis?

Answer 6

eating raw meat

Question 7

Which areas are more affected by toxoplasmosis because of their dietary habits?

Answer 7

France (80%), Quebec (75%), Canadian Inuits (52-66%)

whereas UK and Germany is 15-30%, North America is 30-35%

Question 8

What percentage of livestock pork, lamb and beef are affected by toxoplasma?

Answer 8

3-35% of pork
7-60% of lamb
0-9% of beef

Question 9

Which livestock species is most affected?

Answer 9

leading cause of abortions in sheep

Question 10

What has been developed to protect the sheep but is not effective for other animals?

Answer 10

a live vaccine containing weakened tachyzoites, which do not cause pathology or form bradyzoites or tissue cysts. it is effective for two lambing seasons

Question 11

Who is the definitive host for toxoplasma?

Answer 11

domestic and wild cats. can ingest sporulated oocysts or infected rodents or birds

Question 12

Who is the intermediate/reservoir host?

Answer 12

most warm blooded animals, also birds

Question 13

How can humans obtain the parasite?

Answer 13

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

Question 14

Describe the process of infection of toxoplasma

Answer 14

toxoplasma reproduces asexually in the host

• ingested oocyst goes to digestive tract, where they are engulfed by macrophages
• in macrophages, the tachyzoites develop and travel in the blood stream to various parts of the body
• when immune system is triggered, tachyzoites encyst into pseudocysts that contain bradyzoites

Question 15

Which stages are infectious?

Answer 15

all stages are infectious and can cause toxoplasmosis

Question 16

What are the forms toxoplasma can be found in?

Answer 16

oocysts, tachyzoites, and bradyzoites (tissue cysts)

Question 17

How are the oocysts spread from cats?

Answer 17

in the feces.
cats shed oocysts only 1-2 weeks following infection. the oocysts sporulate and only become infective after 24-48 hours of being air-borne.
can remain viable in moist soil for several years

Question 18

What is contained in the oocyst?

Answer 18

each oocyst has two sporocysts, which each contain four sporozoites

Question 19

How can oocysts be spread?

Answer 19

through seawater. oocysts can remain infectious for mice up to 6 months if carried in seawater

Question 20

Name some characteristics of tachyzoites

Answer 20

• mark the acute phase of infection
• asexual form
• invade all cell types
• rapid multiplication and cell lyses

Question 21

Name some characteristics of bradyzoites

Answer 21

• slow-growing
• form tissue cysts, esp in immunopriveledge regions
• mark the chronic phase
• resistant to low pH and digestive enzymes

Question 22

What are the two phases of the toxoplasma life cycle?

Answer 22

intestinal phase and extraintestinal phase

Question 23

Where does the intestinal phase occur?

Answer 23

in cats only and produces oocysts

Question 24

Where does the extraintestinal phase occur?

Answer 24

in all animals, including cats. produces tachyzoites and bradyzoites

Question 25

What affect does the parasite have on cats?

Answer 25

asymptomatic. sometimes intestinal lesions that can kill kittens

Question 26

What affect does the parasite have on humans?

Answer 26

asymptomatic infections usually. sometimes mild fever, sore muscles, swollen glands and lymph nodes
in immunocompromised individuals, can cause CNS disease, retinochoroiditis, pneumonitis, intracerebral mass lesions

Question 27

When is the fetus at risk of infection and why?

Answer 27

Only when it is the mother’s first infection because she will not have the antibodies to pass to the fetus

Question 28

What does the parasite cause in infected fetuses?

Answer 28

blindness, hydrocephalus (swollen head), seizures, and mental retardation

Question 29

Define congenital toxoplasmosis

Answer 29

When the fetus is infected by toxoplasmosis

Question 30

When is pathology the greatest in the fetus?

Answer 30

during embryonic development, 8-12 weeks after conception

Question 31

What can occur if the fetus becomes infected within the first trimester?

Answer 31

spontaneous abortion, still birth, or severe neurological disease

Question 32

What percent of first-time infected mothers pass the infection to the fetus?

Answer 32

30-40%

Question 33

When is risk of transmission the greatest for the fetus?

Answer 33

in the third trimester, there is a 70% risk

Question 34

What is the risk of infection in early pregnancy?

Answer 34

15%

Question 35

When will the fetus develop the most severe effects to the parasite?

Answer 35

if contracted in the first trimester. will have less severe symptoms in the third trimester

Question 36

What are some common defects seen when the fetus is born?

Answer 36

chorioretinitis (leads to blindness. most common), intra cerebral calcifications, hydrocephaly/microcephaly (least common)

Question 37

How can you diagnose toxoplasmosis?

Answer 37

ELISA tests: IgG and IgM
amniotic/spinal fluid isolation and culture of parasite
microscopy and PCR

Question 38

How does the Sabin-Feldman dye test work?

Answer 38

live virulent toxoplasma tachyzoites are used as antigen and are exposed to dilutions of the serum. so far it is the most specific test to toxoplasma

Question 39

How can you treat toxoplasmosis?

Answer 39

pyrimethamine- antimalarial medication
sulfadiazine- antibiotic used with pyrimethamine
clindamicin- antibiotic used for HIV/AIDS
spiramycin- antibiotic used on pregnant women to prevent infection of fetus

Question 40

How is toxoplasmosis suspected to affect behaviour?

Answer 40

Healthy mice avoid cat urine while infected mice go towards cat urine. this is beneficial for the parasite because the infected mice will get eaten by cats and the toxoplasma life cycle can continue