As stated in Toxoplasma gondii, today I’m going to break down the stages of the parasite. Those stages are:
- Sporulated oocysts (sporozoites) from environment
- Tissue cysts containing bradyzoites in raw/undercooked meat
- Tachyzoites in tissues
- Entero-epithelial stages (only in cats)
Oocysts are produced non-sporulated but will sporulate in about 2 days. They are about 10×10 µm and millions can be produced within days. Cats can develop strong immunity to this stage.
In the intermediate host, the life cycle is as follows:
- Excystation of sporozoites
- Sporozoites –> Tachyzoites
- Tachyzoites disseminate infection and eventually become bradyzoites or tissue cysts
- Latent infection
- Endodyogeny (a form of sexual reproduction)
Tachyzoites have a fondness for neural and cardiac tissue but can infect any nucleated cell in the body. This is the stage that crosses into the placenta and causes congenital infections. Rapid division of tachyzoites is what causes tissue destruction, the spread of infection and lesions.
Bradyzoites (“brady” = slow) are responsible for tissue cysts. They can be present in any organ and survive for the life of the infected animal since they are resistant to the drugs used to treat Toxoplasmosis. If the host is immunocompromised, infection can be reactivated and intermediate hosts can infect one another. Bradyzoites are at fault for initiating meat induced infection, on top of being the only stage to give rise to entero-epithelial stages.
Once again, the etero-epithelial stages are only found in cats. There are 5 types of entero-epithelial schizonts (which will not be listed). This is where the sexual stages/oocysts are produced.
Overall, Toxoplasma gondii was the most successful parasite discussed in my Intro Parasitology course.
:: Information from this post is from my notes from an Introductory Parasitology class taught by Dr. Zajac at Virginia Tech ::
- Mind-Controlling Parasite May Increase Brain Cancer Risk (livescience.com)