Oocysts, bradyzoites, and tachyzoites are the three infectious stages of T. gondii. Tissue cysts may develop in visceral organs, including the lungs, liver, and kidneys, they are more prevalent in the neural and muscular tissues, including the brain, eyes, and skeletal and cardiac muscles. Tissue cysts vary in size; young tissue cysts may be as small as 5μm in diameter and contain only two bradyzoites. While older ones may contain hundreds of organisms. Tissue cysts in the brain are often spheroidal and rarely reach a diameter of 70μm, whereas intramuscular cysts are elongated and may be 100μm long (Dubey et al,. 1998, Dubey, 2010). Transmission electron micrograph of two T. gondii tissue cysts in the brain of a mouse 6 months after infection with the Me-49 strain. The bradyzoites in the younger tissue cyst contain more micronemes and amylopectin than do those in the older tissue cyst. Additionally, the contents of rhoptries in the bradyzoites in the older tissue cyst are electron dense whereas those in the bradyzoites in the younger tissue cyst are honeycombed. The cyst wall (cw) also is more branched and prominent in the older tissue cyst than in the younger tissue cyst (Dubey et al,. 1998). The question is: What factors cause the size of the cysts in the brain to vary? Only time? Strains virulence？What causes the size of the cyst to be close and the size of the cyst to be significantly different?
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Article The Distribution of Toxoplasma gondii Cysts in the Brain of ...
Article The Distribution of Toxoplasma gondii Cysts in the Brain of ...
The parasite forms cysts preferentially in the brain and establishes a chronic infection, which is a balance between host immunity and the parasite's evasion of the immune response. A variety of brain cells, including astrocytes and neurons, can be infected.