The Stages of Toxoplasma gondii

T. gondii constructing daughter scaffolds with...

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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 ::


Parasite Terminology

H. diminuta life cycle.

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:: The image chosen is of the life cycle of a specimen that I actually have a jar full of in my room… ::

Before I dive into aspects about the parasites mentioned in my last post (Trichinella and Toxoplasma gondii), I thought it would be a good idea to post a few definitions of frequently used terms. For future parasite posts, I’ll be sure to try to include a link here to make it easy on new readers, or just in case you’ve forgotten.

  • Life cycle: entire life history including stages and hosts
    • Direct: only one host
    • Indirect: one or more hosts
  • Definitive host: host in which parasite reaches (reproductive) maturity OR sometimes the most important host to us
  • Transport (or paratenic) host: no development occurs, used to get closer to necessary host (eg. marine parasite)
  • Intermediate host: necessary part of life cycle; immature parasite cannot reach maturity without it (eg. heartworms need stage in mosquito before infecting dog)
  • Patent infection: period when parasites are mature and reproduction occurs, parasite produces evidence of infection (eg. eggs)
  • Prepatent period: period following infection before parasites mature; often before infection can detected by microscope
  • Zoonosis: disease transmitted from animal to human
    • Reservoir host: animal carrying infection that can be transmitted to humans
    • Vector: agent (usually arthropod) transmitting disease
  • Helminth: worm
  • Anthelmintic: dewormer
  • Geohelminth: helminth acquired directly from the environment without intermediate hosts or vectors (term used for human intestinal parasites)
:: The information from this post is from my Introductory Parasitology notes taught by Dr. Zajac at Virginia Tech ::

Feral Pigs : From Piglets to Problems

Description: The Wild Boar (Sus scrofa) is the...

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We’ve all gotten the cutesy side of pigs in the media from shows like Winnie the Pooh and his pal Piglet. People also have pigs as pets, not just in a farm environment. Over the years, domestic pigs have escaped their confines leading to feral pigs, also known as wild hogs, wild boars, and razorbacks, among other names. After being introduced to the U.S. by Europe in the 1500s, Sus scrofa hasn’t stuck strictly to captivity. “Within two generations out of captivity, domestic pigs usually lose their pink hue and turn striped and coarse-haired, DePerno said, allowing them to blend in with feral populations” (NG). According to studies, 39 states harbor an estimated 4 million wild pigs.

The hogs can be aggressive both with humans and the environment. Rooting can damage local flora thereby affecting the surrounding fauna and with tusks, usually 3-5″, that have been recorded up to 9″, hogs can easily injure a human. (WDNR) Aside from the dangers their activity poses to agriculture, the environment and humans from physical injuries alone, they also may bring parasites back into the domestic population. The two main parasites of concern are Toxoplasma gondii and Trichinella (which I will address in a later post or two). The parasites can spread through consumption of the meat and can make its way back into domestic populations should the feral pigs come into contact with free range pigs. The consensus seems to be an aggressive approach to eradicating the razorback issue.

Here’s a video about the feral hog issue in one of my very favorite countries, towards the end of which he actually discusses his hunting techniques:


:: I am not big on hunting, nor will I ever be. Sometimes you have to take into account alternative methods in order to put a band-aid on human made problems. ::