Toxoplasmosis Flashcards
Name two toxoplasmosis parasites
Toxoplasma gondii
Sporozoan- Apicomplexa
What is toxoplasmosis?
What does it infect and when was it first discovered?
Intracellular parasite infecting a huge variety of hosts including mammals, reptiles, amphibians, and birds (thought all warm-blooded animals infectable)- primary host is cat?
First discovered in 1908 in a wild rodents and rabbits
Cosmopolitan distribution in human population
When was toxoplasmosis’ medical importance recognised and what does it cause?
Its medical importance not recognised until 1939 when it was identified in tissues of congenitally infected infant
Causes a serious opportunistic infection in AIDS and major cause of birth defects in man and other mammals “Toxoplasmosis is considered to be a leading cause of death attributed to foodborne illness in the United States.”
What does Babesia cause?
The cause of red water disease in cattle
Name some more apicomplexan parasites and what they are common in
Babesia- cause of red water disease cattle
Plasmodium – 2 forms of malaria
Eimeria- common GI protozoal parasite in cattle and birds
Cryptosporidium- common GI protozoal parasite
Toxoplasma gondii
Tell me the following about toxoplasmosis parasites…
- shape
- What they can inhabit
- What they require
- Replication
Shape
Small crescent shaped parasite
Toxo- “bow” Greek
gondii- the North Africa Gundi, first identified host (a north African rodent)
Tachyzoites, (disease causing stage which is ‘bowed) possess a pellicle and subpellicular microtubules (gives the distinctive shape),
What they can inhabit
Can inhabit cytoplasm and nucleus of any nucleated mammalian or avian cell (amphibian / reptile- there is experimental evidence of infection – Stoner and Mannwell, 1969)
What they require
Requires cell to make new proteins so needs to be nucleated
Replication
Replicates within the cell in a parasitophorus vacuole (PV) before rupturing cell and infection of neighbouring cells be found in large numbers in various organs liver, bone marrow, lungs, kidneys brain
A thin layer supporting the cell membrane in various protozoa- seen at the tip
Tell me about the toxoplasma life cycle
cat is primary host- where sexual reproduction occurs
Produces oocysts which release spores to the environment
Sporulated oocyst
This is the only diploid stage the rest is haploid
The only miotic division
Rodent digests this –> GI tract –> sporocysts releases –> enter nucleated cell –> division –> Tachyzoites produced –> released as bradyzoites
Causes immune responses which causes release stage to be damaged
Tachyzoite stage Cyst like bradyzoite stage
Can be life long
Dies or killed and eaten and enter cat
Cat can act as secondary host and repeat all of this
Merogony within the cat (another form of schizogony)
Gametes formed, male and female. Each is haploid which form diploid oocyst which is then shed
The oocyst can be ingested by animals that humans eat
If we eat uncooked met it will infect us, will cause immune response but can’t get rid of all
If cat faeces on veg for instance it can contaminate humans that way
What are the stages of the toxoplasma life cycle seen in the cat?
Merizoite in cat enterocyte, rapidly dividing and then enters meiosis
Gamete
Oocyst (red)and sporulated oocysts (black) in intestine
Encysted Bradyzoites in neuron – cat can be a secondary host too
What are the stages of the toxoplasma life cycle seen in the secondary host?
NB. All stages are infectious
Rapidly dividing tachyzoites
Slowly dividing (?) bradyzoites- found in tissue cysts
Whats the routine cycle of the toxoplasma?
Cats the definitive host (here sexual replication of Toxoplasma gondii takes place)
Merogony replication of merozoites followed by gametogony in cat enterocytes- both forms of schizogony- male and female T. gondii gametes forms and fuse to form diploid oocysts
Replication of merozoites in cat enterocytes (male and female T. gondii gametes formed and fuse to form diploid oocysts)
Oocysts shed in faeces and undergo meiosis in the environment giving eight haploid sporozoites. (All other stages are haploids other than the oocyst)
In the intermediate host (in most cycles rodents), asexual replication occurs.
- Acute infection tachyzoites (rapidly replicating forms) that disseminate throughout the body.
- chronic infection- tachyzoites differentiate (driven by host immune response) to slow-growing bradyzoites within tissue cysts
Ingestion of tissue cysts by cats, re-initiating the sexual phase of the life cycle (cats can also act as secondary hosts)
Oocysts survive in the environment for long periods of time, can sporulate and contaminate food and water.
What are some other toxoplasma hosts?
How do they become infected?
Many animals serve as intermediate hosts,
including human and farm animals-these become infected by
- eating undercooked meat containing tissue cysts
- ingesting sporulated oocysts in contaminated water and food
- congenital infection. - blood transfusion- tissue transplantation
Why is toxoplasma possibly one of the most widespread parasites in the world?
Cats release millions of oocysts after ingesting only one bradyzoite or one tissue cyst
Tens of thousands of tissue cysts may be present in one infected mouse (or other second host)
Sporulated oocysts survive for long periods under most ordinary environmental conditions.
Invertebrates such as flies, cockroaches, dung beetles and earthworms can mechanically spread these oocysts and carry them to food (vegetables etc)
Congenital infection can occur in cats (and secondary host), congenitally infected kittens can produce oocysts for contamination.
Infection rates in cats reflect the rate of infection in local avian and rodent populations as they serve as prey for cats
Huge range of secondary hosts
T. gondii may survive in intermediate host lifelong as tissue cysts- all edible portions of animal can harbour viable T.gondii. and all stages are infectious
Organ transplantation and blood transfusion: from implantation of an organ or bone marrow from an infected donor or from latently infected person
Usually doesn’t kill either of its hosts
Can Tachyzoites induce both cell mediated and humoral responses?
Yes
T. gondii invades host cells lives in intracellular niche- protected from much of the immune system, further the CNS shows immune restriction…
What does it cause?
- Causes a modified host lipid membrane to surround the parasite, the parasitophorous vacuole (PV)
- Inhibits apoptosis in host cell
- Prevents lysosomal fusion with the PV
Specific parasite organelles, called the micronemes, rhoptries and dense granules, contain proteins that alter host cell function –
What does it cause?
- cause a modified host lipid membrane to surround the parasite, the parasitophorous vacuole (PV).
- Inhibits apoptosis in host cell
- prevents lysosomal fusion with the PV. The membrane of PV contains parasite specific nutrient transporters
The severity of congenital infection depends on what?
Severity of congenital infection depends upon stage of pregnancy when infected
- Spontaneous abortions
- Hepatic defects
- Hydrocephalus,
- Intra-cerebral calcifications,
- Chorioretinitis
What is the treatment for the acute stages of toxoplasmosis?
