– Scientific Classification –
- Domain: Eukaryota
- Kingdom: Chromalveolata
- Superphylum: Alveolata
- Phylum: Apicomplexa
- Class: Conoidasida
- Subclass: Coccidiasina
- Order: Eucoccidiorida
- Family: Sarcocystidae
- Genus: Toxoplasma
- Species: T. gondii
Toxoplasma gondii was first described in 1908 after being found in the gundi ( a North African rodent). It is found in most mammals and birds with cats as a definitive host and a rodent as a common intermediate host as well as humans and other warm-blooded animals. Tissue cysts, the asexual stage of the parasite, occur in the intermediate host while the sexual stages and oocysts occur in the definitive host. Oocysts develop in the environment, after being excreted in the feces, where they sporulate. Infection, called Toxoplasmosis, can lead to ocular infections, immunosuppression, and organ transplantation. Congenital infections (pregnant female with the infection, infects fetus) were recognized in humans in 1923.
The different stages of T. gondii are:
- Sporulated oocysts (sporozoites) from environment
- Tissue cysts containing bradyzoites in raw/undercooked meat
- Tachyzoites in tissues
- Entero-epithelial stages only in cats
[These stages will be broken down in a later post.]
Cases of Toxoplasmosis are most severe in congenitally infected young or an immunosuppressed individual. Common conditions after infection are pneumonia, hepatitis, encephalitis and ocular disease. Tachyzoites cause tissue destruction but the cysts do not cause lesions or an immune response.
- Congenital infections
- AIDS (Toxoplasmic encephalitis)
- Organ transplantation
Sources of human Toxoplasmosis include undercooked meat containing tissue cysts (such as pork in the U.S., lamb or goat in other countries and meat from wild animals), and oocysts from contaminated produce, soil, water, litter boxes, etc. A previous infection may not always prevent congenital infection if the strain acquired by the mother is genetically different. Maternal testing for Toxoplasmosis is not required in the U.S. but is by law in France and Austria. Sera is tested for antibodies and if results are negative, the patient is retested monthly. If positive, doctors must rule out recent or active infection.
In animals, T. gondii infections are mostly asymptomatic. It can cause abortions in sheep, goats and pigs but only a generalized infection in cats. Infection is fatal to Australian marsupials, arboreal monkeys, lemurs and perhaps certain avian species.
:: Information from this post is from my notes from an Introductory Parasitology class taught by Dr. Zajac at Virginia Tech ::