Fifth disease: An oddly named disease caused by a virus called parvovirus B 19. (In the pre-vaccination era, fifth disease was frequently the "fifth disease" that a child contracted.) . Symptoms include low-grade fever, fatigue, a "slapped cheeks rash," and a rash over the whole body.
While the illness is mild in most children, some children with immune deficiency (such as those with AIDS or leukemia) or with certain blood disorders (such as sickle cell anemia or hemolytic anemia) may become seriously ill with fifth disease. Parvovirus B19 can temporarily decrease or halt the body's production of red blood cells, causing anemia.
Moreover, fifth disease is of consequence in many adults. About 80% of adults with fifth disease have joint aches and pains (arthritis) which may become long-term with stiffness in the morning, redness and swelling of the same joints on both sides of the body (a "symmetrical" arthritis), most commonly involving the knees, fingers, and wrists.
Pregnant women (who have not previously had the illness) should avoid contact with patients who have fifth disease. The fifth disease 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.
Fifth disease is also known as erythema infectiosum. For more information, read the article on Fifth Disease.