Toxoplasma Flashcards
Which species belong to the toxoplasma species?
toxoplasma gondii is the only species in the genus
Where is this parasite found?
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
What are the effects of toxoplasmosis?
asymptomatic in healthy adults- will form cysts in immunologically privileged sites
can cause the death of the fetus
Why does increased infection occur in older individuals?
bope, but it does
Why is the frequency of infection higher in Central America?
because their is a greater number of stray cats and the climate favours oocysts (esp. when in soil).
lower altitudes also favour the disease
What dietary habit increases the frequency of toxoplasmosis?
eating raw meat
Which areas are more affected by toxoplasmosis because of their dietary habits?
France (80%), Quebec (75%), Canadian Inuits (52-66%)
whereas UK and Germany is 15-30%, North America is 30-35%
What percentage of livestock pork, lamb and beef are affected by toxoplasma?
3-35% of pork
7-60% of lamb
0-9% of beef
Which livestock species is most affected?
leading cause of abortions in sheep
What has been developed to protect the sheep but is not effective for other animals?
a live vaccine containing weakened tachyzoites, which do not cause pathology or form bradyzoites or tissue cysts. it is effective for two lambing seasons
Who is the definitive host for toxoplasma?
domestic and wild cats. can ingest sporulated oocysts or infected rodents or birds
Who is the intermediate/reservoir host?
most warm blooded animals, also birds
How can humans obtain the parasite?
by ingesting a cyst, eating raw meat, transplacentally or through organ transplants
Describe the process of infection of toxoplasma
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
Which stages are infectious?
all stages are infectious and can cause toxoplasmosis
What are the forms toxoplasma can be found in?
oocysts, tachyzoites, and bradyzoites (tissue cysts)
How are the oocysts spread from cats?
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
What is contained in the oocyst?
each oocyst has two sporocysts, which each contain four sporozoites
How can oocysts be spread?
through seawater. oocysts can remain infectious for mice up to 6 months if carried in seawater
Name some characteristics of tachyzoites
- mark the acute phase of infection
- asexual form
- invade all cell types
- rapid multiplication and cell lyses
Name some characteristics of bradyzoites
- slow-growing
- form tissue cysts, esp in immunopriveledge regions
- mark the chronic phase
- resistant to low pH and digestive enzymes
What are the two phases of the toxoplasma life cycle?
intestinal phase and extraintestinal phase
Where does the intestinal phase occur?
in cats only and produces oocysts
Where does the extraintestinal phase occur?
in all animals, including cats. produces tachyzoites and bradyzoites
What affect does the parasite have on cats?
asymptomatic. sometimes intestinal lesions that can kill kittens
What affect does the parasite have on humans?
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
When is the fetus at risk of infection and why?
Only when it is the mother’s first infection because she will not have the antibodies to pass to the fetus
What does the parasite cause in infected fetuses?
blindness, hydrocephalus (swollen head), seizures, and mental retardation
Define congenital toxoplasmosis
When the fetus is infected by toxoplasmosis
When is pathology the greatest in the fetus?
during embryonic development, 8-12 weeks after conception
What can occur if the fetus becomes infected within the first trimester?
spontaneous abortion, still birth, or severe neurological disease
What percent of first-time infected mothers pass the infection to the fetus?
30-40%
When is risk of transmission the greatest for the fetus?
in the third trimester, there is a 70% risk
What is the risk of infection in early pregnancy?
15%
When will the fetus develop the most severe effects to the parasite?
if contracted in the first trimester. will have less severe symptoms in the third trimester
What are some common defects seen when the fetus is born?
chorioretinitis (leads to blindness. most common), intra cerebral calcifications, hydrocephaly/microcephaly (least common)
How can you diagnose toxoplasmosis?
ELISA tests: IgG and IgM
amniotic/spinal fluid isolation and culture of parasite
microscopy and PCR
How does the Sabin-Feldman dye test work?
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
How can you treat toxoplasmosis?
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
How is toxoplasmosis suspected to affect behaviour?
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
