A 28 yrs old obstetric patient becomes acutely ill during her first trimester with infectious mononucleosis-like symptoms, but her heterophil antibody test was negative. A careful history reveals that the family has two cats in the house. The appropriate laboratory tests indicate the expectant mother is infected with Toxoplasma gondii. Months later, the woman delivers a full term baby with no obvious signs of infection with the protozoan parasite. The best test to diagnose acute infection in the neonate would be a parasite-specific ELISA for which isotype of immunoglobulin?
A. IgA
B. IgE
C. IgG 1
D. IgG 4
E. IgM