Congenital toxoplasmosis

A 35-year-old primigravid woman has a stillbirth at 21-weeks of gestation. The patient has been consistent with her prenatal care and taking daily prenatal vitamins. She returned from a trip to Nigeria 6 months ago. Past medical history is notable for type I diabetes mellitus. She developed a fever, swollen lymph nodes, and muscle aches during the pregnancy that lasted for a week. A fetal autopsy is notable for scattered intracranial calcifications, hydrocephalus, macrocephaly, and hepatosplenomegaly. Which of the following maternal exposures most likely resulted in this fetus’s condition?