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[Toxoplasma gondii]

Tachyzoites (trophozoites) of Toxoplasma 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	B

A:  Formalin-fixed T. gondii tachyzoites, stained by immunofluorescence (IFA).  This is a positive reaction (tachyzoites + human antibodies to Toxoplasma + FITC-labelled antihuman IgG = fluorescence.)
B:  Negative IFA for antibodies to T. gondii.

C

C:  Negative IFA for antibodies to T. gondii, polar stain reaction.