Slapped cheek syndrome is caused by parvovirus B19. A parvovirus B19 infection is spread in the same way as a cold or flu.
It can be spread inside infected droplets of saliva that can be:
- inhaled in by other people when you cough or sneeze
- left on surfaces which other people can touch and then transfer into the body by touching their mouth or nose
A child is most contagious three to seven days before the appearance of the distinctive red rash.
Humans are not born with immunity to parvovirus B19, which is why most cases occur in children. Once infected, a person usually develops a lifelong immunity to further infection.
Children old enough to attend nursery or school are most at risk of infection because of their close proximity to lots of other children. It's also common for older children to pass the infection along to younger brothers and sisters.
Adults who haven’t previously had the infection are most at risk if they work with children, including teachers and nursery workers.
How the virus affects the body
Once parvovirus B19 enters the body, it targets cells called erythroid progenitor cells which are found in bone marrow and blood. It is the fact that the parvovirus B19 infection targets blood and bone marrow that makes it a particularly serious infection for people with blood and bone marrow disorders.
Most of the symptoms of a parvovirus B19 infection, such as the red rash, are not caused by the virus itself but by the immune system releasing antibodies to kill the virus.
