Serological responses in Sarcocystis cruzi infected calves challenged with Toxoplasma gondii

Three four-week-old calves were used in a study on serological responses in combined Sarcocystis cruzi and Toxoplasma gondii infections. One calf (C1) was inoculated orally with 100,000 S cruzi sporocysts, another (C2) with 40,000 sporocysts, while the third (C3) acted as uninfected control. One hundred and five days later, all three calves were inoculated orally with 100,000 T gondii oocysts. The antibody responses to sarcocystis and toxoplasma during 210 days were recorded, using different serological assays. During the S cruzi monoinfection phase, positive antibody reactions were recorded in C1 and C2, using an ELISA with soluble (cytoplasmic) T gondii tachyzoite antigen, while antibody reactions remained negative in the toxoplasma indirect fluorescent antibody test and in an ELISA employing T gondii tachyzoite cell membrane antigen. However, the Sabin Feldman dye test also showed transient low positive titres for C1 and C2 at around day 39 after S cruzi inoculation. When using an ELISA employing soluble S fusiformis cystozoite antigen, increased sarcocystis antibody counts were recorded for C1 and C2 starting two weeks after T gondii inoculation. Otherwise the three calves reacted as expected regarding the general antibody responses to the S cruzi and T gondii infections.