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 light reddish "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.

Veterinarians are aware that one form of parvovirus (canine parvovirus type 2) is highly contagious in dogs and can produce gastrointestinal infection with severe bloody diarrhea, as well as cytopenias. Young dogs and puppies are most affected. A vaccine is available.