Erythema infectiosum, or "fifth disease", is a common infection of childhood caused by a virus. The term "fifth disease" does not refer to someone named "Fifth", but rather to the fifth of six classic exanthems, or rash-associated diseases, of childhood. The numbering is of historic interest only: the other examthems, in order, are:
The virus responsible for erythema infectiosum is parvovirus B19, a virus that lives only in humans. It seems to be transmitted mainly by body fluids, including droplets produced when you cough or sneeze but also including blood. Symptoms usually appear within 4 days to 2 weeks after exposure, but may take as long as 3 weeks. The virus seems to be less contagious once the rash appears (so children with the rash can go to school or day-care without exposing others).
The most common symptoms of fifth disease are mild cold symptoms and malaise, fever in up to 1/3 of patients, and a rash. On the body this rash is usually light red and lacy in appearance -- the typical rash does not look like measles, but some pediatricians refer to it as "Hungarian measles". Occasionally a child with this virus has a rash that looks very much like that of rubella, but this is not common. The best-known rash of fifth disease is on the face, which becomes intensely red, especially on the cheeks, with a pale ring around the mouth ("circumoral pallor"). The child's face looks like her cheeks have been slapped, and the uninitiated may look at a child with fifth disease and think that the child was slapped across the face. (The child protection workers in the area where I practice are acquainted with fifth disease and its appearance. Good thing, too.) In addition, joint pain can occur: it's relatively rare in kids but more common in adults. (When joint pain due to fifth disease does happen in children it most often involves the knees; in affected adults the joint problems are seen in knees, fingers, and other joints, and usually corresponding joints on both sides of the body are affected.) Many people (adults and children) are infected with parvovirus B19 and show no symptoms whatever. However, some people with immune system problems may develop chronic parvovirus B19 infection, and may remain contagious for up to a week after the symptoms begin.
Although very rare, parvovirus B19 infection can produce more severe results. These include anemia caused by hemolysis (breakdown of red blood cells). People with abnormalities in their hemoglobin, such as those with sickle-cell disease, may develop an "aplastic crisis". It is also possible for parvovirus B19 infection during pregnancy to cause "hydrops" (fluid overload and heart failure) in the developing fetus; however, this happens in less than 10% of mothers with proven parvovirus infection in the first trimester (which probably means that the risk is much less than 10%, since many infections go unnoticed). The risk of fetal death is about 2-6%, with the greatest risk in the first half of pregnancy. No one has shown that parvovirus B19 infection during pregnancy is associated with birth defects.
There is presently no vaccine available for parvovirus B19, and no good and simple test for it outside of hospital and research laboratories. Since so many infections occure without any symptoms, people are always at risk of exposure unless they have already had the disease. Like many other viruses, once you have been infected you are likely to be immune for life. People who spend a lot of time with children (like other children, as well as teachers, day-care workers, and parents) are more likely to be exposed.
Since the virus is so widespread, and since problems with the fetus after an infection are so uncommon, infectious-diease authorities feel that keeping pregnant women away from children or adults known to have the virus will not eliminate the risk of infection. If you are a pregnant woman and find out that you have been exposed to a known or suspected case of fifth disease, you should talk to your obstetrician. It is possible to be tested to see if you are immune to parvovirus: if you are immune, your baby is not at risk. Ultrasound may help detect problems with the fetus should they occur.
Children with fifth disease who have the rash may go to school or day care without exposing others further (by the time the rash appears the child is no longer contagious). Good handwashing will help you keep from giving the bug to others. As with other viruses, there are no antibiotics that will treat a parvovirus infection. Immune globulin may help in severe cases, such as aplastic crises or in people with immune-system problems, but is never used for mild cases.
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