The large pink inclusion in the erythroid precursor seen here in fetal spleen is evidence for parvovirus infection. Parvovirus, or "fifth" disease, produces a mild illness in children, marked by a "slapped cheek" facial rash. In adults, the illness often goes unnoticed, but pregnant women can pass the virus to the fetus, where it may produce marked fetal anemia and hydrops in some cases.

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