Toxoplasmosis is a disease caused by Toxoplasma gondii, an obligate intracellular protozoan. This parasitic disease is transmitted orally or congenitally and causes acute and chronic infection. Primary forms of transmission to humans are contact with cat feces and eating uncooked meat, primarily pork, lamb, and wild game. Toxoplasma cysts have a slight argyrophilic nature and will stain with periodic acid-Schiff (PAS) in varying intensities. The organism has three forms:
- Tachyzoite: 4-8 microns (µ), crescent to oval shape and are present in acute infections
- Tissue cysts: 10-100 µ, contains up to 3,000 organisms
- Oocysts: 10-12 µ, produced in the intestine of cats
IHC demonstration of T. gondii on FFPE tissue sections using IgG2a mouse monoclonal antibody clone TP3 requires heat-induced epitope retrieval (HIER) pretreatment using citrate buffer.
A toxoplasmosis infected lung seen by hematoxylin and eosin (H&E) stained section is shown in the top image. Notice the cluster of T. gondii within this tissue cyst. The cyst will rupture, releasing individual protozoa to form new cysts. The lower image is T. gondii mouse monoclonal antibody, clone TP3, using DAB chromogen. You can again notice the cluster of T. gondii protozoa within this tissue cyst, which will rupture and release the individual protozoa to form new cysts.