Microscopy Findings

Humans only serve as an intermediate host for Toxoplasma gondii; the oocysts are shed only in the feces of wild and domestic felids.  Tachyzoites (trophozoites) of T. gondii are approximately 4-8 µm long by 2-3 µm wide, with a tapered anterior end, a blunt posterior end and a large nucleus.  They may be found in various sites throughout the body of the host.

A

A: Toxoplasma gondii tachyzoites, stained with Giemsa, from a smear of peritoneal fluid obtained from a laboratory-inoculated mouse.

Cysts of Toxoplasma gondii usually range in size from 5-50 µm in diameter.  Cysts are usually spherical in the brain but more elongated in cardiac and skeletal muscles.  They may be found in various sites throughout the body of the host, but are most common in the brain and skeletal and cardiac muscles.

B	C

B: Toxoplasma gondii cyst in brain tissue stained with hematoxylin and eosin.
C: Higher magnification of Figure B.