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Kinetics of Circulating Antigens and DNA Detections in Acute Murine Toxoplasmosis.

Khalifa El Sayed Khalifa.

Department of Parasitology, Faculty of Medicine, Ain Shams University.

The kinetics of detection of anti-Toxoplasma antibodies and circulating Toxoplasma antigens (Cags) in mice sera in relation to detection of parasite DNA in blood and different organs following acute murine toxoplasmosis was investigated. C57BL/10 mice were infected by intraperitoneal injection of 10 cysts of the avirulent KSU Toxoplamsa gondii strain. Blood, brain, liver, spleen and lung samples were collected thereafter at daily intervals for 2 weeks and then twice weekly for 2 weeks. Sera were tested for antibodies by Sabin Feldman dye test and for Cags by ELISA. Brain, liver, spleen, lung and leukocytes were examined by PCR using primer sets derived from the B1 gene of Toxoplasma. Cags were detected starting from day 5, this coincided with multiplication of the parasite in the liver, spleen and lung as revealed by the amplification of the target 223 bp DNA segment from these organs. The amount of Cags increased gradually and peaked between days 7 and 9, this was associated with the appearance of the parasite in the brain tissue. Antibodies started to appear starting from day 12 and coincided with the encystation of the parasite in the brain, as seen microscopically, and with a decrease in the amounts of Cag. There were no amplifications of parasite DNA from blood throughout the experiment. This study indicates that the detection of circulating antigens is valuable during acute phase of the disease. Antibodies appear later than antigens and increase gradually to reach a stable titer with establishment of infection in the body. The study also indicates that lung and brain are the most common pathologic target for toxoplasmosis as evidenced by the distribution of the parasite in the body post-infection. Examination of blood by PCR may give negative results in cases with established Toxoplasma infection of body organs.