This is a benign illness of school age children and is caused by a human parvovirus designated B19 which is not related to canine parvovirus. The rash occurs at 10-14 days and represents an immune response. The rash is characteristic. The person with the illness is infectious before but not after the rash appears. Rare complications of parvovirus include a loss of white cells in the blood and long term anaemia.
Foetal problems can develop in pregnant women.
Few infected individuals can find a source for the illness and the diagnosis is made more easily when there is a known outbreak of the disease. The rash is usually the first sign of illness. The rash appears on the cheeks as raised red lumps that join to give a 'slapped cheek' appearance and may also occur on the forehead, chin and behind the ears as single spots, but not around the mouth. The lesions are warm, non-tender and often itchy. Within 1-2 days lesions appear on the upper arms and legs and spread down the limbs, with palms and soles spared.