<i>Toxoplasma gondii</i> acute infection: Estimation of humoral response and blood parasitism in mice AS/n inbred <b>[Abstract in English]</b>

Abstract

AIMS: To analyze experimentally the humoral immune response in acute and recent chronic infections by Toxoplasma gondii and its correlation with the blood parasitism. METHODS: Ten female mice AS/n inbred strain orally infected with 10 cysts per animal from Toxoplasma gondii ME-49 strain were evaluated during 60 days. Blood collections were made in each 3-4 days. Blood parasitism was evaluated by polymerase chain reaction, and antibody titres by enzyme-linked immunosorbent assay and indirect immunofluorescence. RESULTS: Positive polymerase chain reaction was detected around seven day-intervals until the 28th day and was negative after the 30th day pos-infection. Sera assayed by immunofluorescence presented IgM antibodies after the 7th day of infection and high titers were found between the 18th and 27th day. After 30 days, IgM titers were low until the 60th day. IgG antibodies were produced around the 14th day and were high until the 60th day. The avidity and kinetic exhibited by IgG antibody levels increased from the 14th day and the avidity percents increased with maximum peak after 28 days, establishing the chronic infection. CONCLUSIONS: These data emphasize that tachyzoites can be detected in blood during the acute phase of toxoplasmosis, even though the protective immune response was already developed.