The relationship between seropositivity and tissue cysts in sheep naturally infected with Toxoplasma gondii

Skeletal muscles (tongue, masseter, leg, intercostal, and diaphragmatic muscles) and brain samples of 100 sheep at slaughter were analysed for the presence of T. gondii tissue cysts along with serum IgG titres. Two methods of isolation by percoll gradient centrifugation and tissue microarray (TMA) technique with immunoperoxidase staining were used. Seropositivity was detected in 88% (88/100) of sheep sera analysed by indirect fluorescent antibody test. Tissue cysts were observed in 46 (52.3%, 46/88) and 15 (17%, 15/88) of the seropositive sheep with the isolation technique and TMA and immunoperoxidase staining, respectively. The diameters of the tissue cysts were 25-58 x 25-62 (mean 34 x 36) mu m. The relationship between the presence of tissue cysts and seropositivity in sheep was statistically significant at 1/16 (P < 0.01) and at 1/64 and 1/128 (P < 0.001) serum dilutions.