Pregnancy danger from fifth disease: Caused by a virus known as parvovirus B 19. Symptoms include low-grade fever, fatigue, a "slapped cheeks rash," and a rash over the whole body. Pregnant women (who have not previously had the illness) should avoid contact with patients who have fifth disease. The virus can infect the fetus prior to birth. And, while no birth defects have been reported as a result of fifth disease, it can cause the death of the unborn fetus. The risk of fetal death is 5%-10% if the mother becomes infected. The illness is not serious in children.