Toxoplasma may be detected on histopathology in one of two forms: tachyzoites or cysts. Tachyzoites are crescent-shaped and usually establish the diagnosis of acute infection. Cysts are circular in shape and may represent latent infection or reactivation disease, depending on the host. Images of cysts and tachyzoites can be found at the US Department of Agriculture website at http://www.ars.usda.gov/Main/docs.htm?docid=11013.
Stages of Toxoplasma gondii. Scale bar in A-D= 20 ?m, in E-G = 10 ?m.
A. Tachyzoites in impression smear of lung. Note crescent-shaped individual tachyzoites (arrows), dividing tachyzoites (arrowheads) compared with size of host red blood cells and leukocytes. Giema stain.
B. Tissue cysts in section of muscle. The tissue cyst wall is very thin (arrow) and encloses many tiny bradyzoites (arrowheads). Hematoxylin and eosin stain.
C. Tissue cyst separated from host tissue by homogenization of infected brain. Note tissue cyst wall (arrow) and hundreds of bradyzoites (arrowheads). Unstained.
D. Schizont (arrow) with several merozoites (arrowheads) separating from the main mass. Impression smear of infected cat intestine. Giemsa stain.
E. A male gamete with two flagella (arrows). Impression smear of infected cat intestine. Giemsa stain.
F. Unsporulated oocyst in fecal float of cat feces. Unstained. Note double layered oocyst wall (arrow) enclosing a central undivided mass.
G. Sporulated oocyst with a thin oocyst wall (large arrow), 2 sporocysts (arrowheads). Each sporocyst has 4 sporozoites (small arrow) which are not in complete focus. Unstained.
REF. UpToDate 2018.07.07
