Contagiousness
A person with parvovirus infection is most contagious before the rash appears — either during the incubation period (the time between infection and the onset of symptoms) or during the time when he or she has only mild respiratory symptoms. Because the rash of fifth disease is due to an immune reaction (a defense response launched by the body against foreign substances like viruses) that occurs after the infection has passed, a child is usually not contagious once the rash appears.
Parvovirus B19 spreads easily from person to person in fluids from the nose, mouth, and throat of someone with the infection, especially through large droplets from coughs and sneezes.
In households where a child has fifth disease, another family member who hasn't previously had parvovirus B19 has about a 50% chance of also getting the infection. Children with fifth disease may attend childcare or school, since they are no longer contagious. Once infected with parvovirus B19, a person develops immunity to it and won't usually become infected again.
Parvovirus B19 infection during pregnancy may cause problems for the fetus. Some fetuses may develop severe anemia if the mother is infected while pregnant — especially if the infection occurs during the first half of the pregnancy. In some cases, this anemia is so severe that the fetus doesn't survive. Fortunately, about half of all pregnant women are immune from having had a previous infection with parvovirus. Serious problems occur in less than 5% of women who become infected during pregnancy.