The facts about...

Parvovirus infection

What is a parvovirus infection ?

Parvovirus B19 is a small DNA virus which was discovered by chance in 1975. The virus is spread by infected respiratory droplets and the illness usually starts after an incubation period of between four and fourteen days. Patients are usually no longer infectious once the characteristic rash of this disease has appeared. Any age may be affected although it is most common in children aged six to ten years. By the time adulthood is reached about half the population will have become immune following infection at some time in their past. Outbreaks can arise especially in nurseries and schools. A significant increase in the number of cases is seen every three to four years; the last epidemic year was 1998. Parvovirus is also known as "fifth disease" because it was the fifth cause of a superficial red rash of childhood to be identified. Other similar rashes include measles, rubella [German measles] and scarlet fever. Parvovirus B19 only causes an infection in humans; cat and dog parvoviruses do not infect humans.

What symptoms does a parvovirus infection cause ?

Up to a third of those infected will have no symptoms at all. Patients who do develop the disease often have a mild flu-like illness from which there is usually a rapid recovery. Between 15-30% of patients will develop erythema infectiosum which gives a characteristic slapped cheek appearance. This gives rise to another name for this infection of the "slapped cheek" syndrome. The rash may spread to the arms, legs and body. It fades quickly but may recur a few weeks later following exposure to sunlight or heat. Adult women in particular can also develop acute painful and swollen joints which may persist for several months. Patients who have an existing illness which affects their immune system, such as AIDS, may develop a chronic type of anaemia and may remain infectious for several weeks. Parvovirus infections can cause a temporary bone marrow disorder in patients with a pre-existing chronic blood problem, such as sickle-cell disease or hereditary spherocytosis.

Parvovirus infections and pregnancy

Approximately 60% of women in the United Kingdom are immune to parvovirus due to having this illness in the past. If a pregnant woman develops a parvovirus infection there is no strong evidence that congenital or developmental abnormalities will occur in the baby. There is no indication for termination of pregnancy in these circumstances. There is minimal risk to the foetus if the infection is caught after the pregnancy has reached 20 weeks. However before 20 weeks there is an extra 9% risk of miscarriage and a 3% risk of a condition called hydrops foetalis when the foetus develops anaemia and heart failure. Hydrops foetalis can be diagnosed by a series of ultrasound scans and treated by blood transfusions while the foetus is still in the womb.

How is a parvovirus infection diagnosed ?

Often the infection is diagnosed by the clinical features alone. When it is considered necessary to confirm a parvovirus infection, for example during pregnancy, then blood samples can be tested in a laboratory. The finding of parvovirus B19 IgM antibodies in a blood sample is consistent with a recent infection. By comparison, only finding parvovirus B19 IgG antibodies indicates an infection some time in the past and the patient now has life-long immunity. The absence of both parvovirus B19 IgG and IgM antibodies indicates there has been no recent or previous infection and the patient remains susceptible to the disease.

How is a parvovirus infection treated ?

There is no specific treatment available. If necessary patients are given medicines to relieve their symptoms such as analgesics for joint pain. Severe anaemia in patients whose immune system is deficient or those who have chronic blood disorders can be treated with blood transfusions.

Can parvovirus infections be prevented ?

At present there is no vaccine to prevent this infection. Pregnant women should be given advice about parvovirus but there is no indication for routine antenatal screening for parvovirus B19 immunity. Any pregnant woman who comes into contact with a known or suspected case of parvovirus should consult their general practitioner or midwife. Blood tests can then be performed to determine if the woman is presently susceptible or immune to a parvovirus infection. This information will help to determine what further action, if any, needs to be taken. There is no reason to keep a child with parvovirus infection off school unless the child is unwell. However in hospital units which care for patients with deficient immune systems then it may be necessary to isolate and "barrier nurse" patients with a parvovirus infection to help prevent the infection spreading to other susceptible patients.