Toxoplasma gondii
Kristen King

Toxoplasma gondii is a member of the eukaryote family, more specifically, Protists.  It is related to Plasmodium, which is the parasite that causes malaria.  T. gondii has two distinct life cycles, in which it requires two different hosts to complete the cycles.  Usually, it calls for a member of the cat family (felidae), wild or domestic, and mice or rats.  However, when the parasites ideal hosts are not readily available, it will infect other mammals such as humans.

T. gondii is crescent shaped; they are not flagellated and do not exhibit cilia.  They glide on solid substrates for motility and they leave a trace of a surface membrane protein called SAG1 behind.  This trail can be detected by staining with antibodies.  The motility depends on the actin cytoskeleton of the parasite.

Toxoplasmosis is the infection that is caused by Toxoplasma gondii.  It has a wide spectrum of medical syndromes in mammals such as humans, land and sea animals and a variety of bird species.  Persons at risk for toxoplasmosis include fetuses, newborns, and immunologically impaired patients.  In immunodeficient individuals, toxoplasmosis occurs mostly in people with T-cell-mediated immunity, such as people with bone marrow and organ transplants, or AIDS.  Some of the symptoms of toxoplasmosis include: fever, lack of coordination, nausea, seizures, headaches, and confusion.

The two different life cycles are the sexual cycle and the asexual cycle.  The sexual cycle only occurs in cats.  The stages of this cycle are cyst, oocyst, or tachyzoite.  First, the cat may eat cyst infected birds, rodents or raw meat.  The cysts are also known as bradyziotes.  The bradyzoites fuse to form zygotes, which multiply in the small intestine wall and become oocysts.  At this point, millions of oocysts are excreted in the cat’s feces for two to three weeks.  The oocysts are very strong and can remain infectious in moist, shaded soil and sand for many months; and can remain infectious for more than a year in warm, humid environments.

The asexual cycle occurs in other mammals, such as humans and birds.  Infection occurs by ingestion of oocysts through handling of contaminated soil or cat litter, and the consumption of contaminated water or food sources such as unwashed garden vegetables.  It can also occur through consumption of undercooked or uncooked meat or through transplantation of an organ that contains cysts.  Transmission of T. gondii to the fetus occurs through the placenta after maternal infection.  This is what usually causes Toxoplasmosis and can result in stillborn or miscarriage.

I chose Toxoplasma gondii as my microbe of the week because I found it interesting that 50% of the American population and 20% to 80% of domestic animals are infected with T. gondii in its cyst form, yet no vaccinations have been developed yet.  In addition, I was also curious about this microorganism because while I was pregnant with my daughter, my friends and family were all very adamant about keeping me away from their cats, in fear that if I had too much contact with them, I might lose the baby.  I had heard of an organism associated with cats causing miscarriage and stillborn but, never took the time to research it until now.  I also chose this microorganism because in my research, I have found that it is sometimes linked to encephalitis (swelling of the brain), which my father-in-law developed in 1995.  At the time of his infection, he suffered all of the symptoms listed above, which rendered him in a vegetative state for close to a year.  He is still has not fully recovered.  He has 2 cats and continues to clean their litter boxes every day or every other day.


*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.


Return to Missouri S&T Microbiology HomePage Go to DJW's HomePage