Kinetics and time dependence of the differential agglutination of acetone [AC]- and formalin [HS]-fixed Toxoplasma tachyzoites by serum of mice with experimental toxoplasmosis.

Researches to specify a serologic diagnostic test capable of determining the stage of toxoplasmosis, whether recent or latent, have been hampered by lack of knowing the real time of infection. Studying the precise kinetics of the differential agglutination of acetone [AC]-fixed versus that of formalin [HS]-fixed tachyzoites (differential agglutination test or AC/HS test) by sera of mice during the course of toxoplasmosis and assessment of its value in the differentiation between recent and latent infections in mice were the aims of the present work. Experimental toxoplasmosis was induced in mice, sera were collected sequentially and AC/HS test, FAST-ELISA to determine levels of IgM and IgG and microscopic examination of brain for Toxoplasma cysts were done. Both AC and HS specific patterns in the AC/HS test were noted to be dependent on the time from the onset of infection. Acute patterns of the AC/HS test were observed early in infection till before the appearance of brain cysts. Non-acute patterns were obtained late on 28th day post infection coinciding with the disappearance of IgM, persistence of IgG and presence of cysts in brains. The AC antibody was high in the recent phase of infection, and then it declined to be replaced by high sustained level of HS antibody late in infection. In conclusion, in the presence of both IgM and IgG, the appearance of either equivocal pattern or the non-acute pattern in the AC/HS test is significant in ruling out acute infection in mice.