Fifth disease overview

# Overview
The fifth disease sometimes called erythema infectiosum, is a mild rash illness caused by a viral infection that occurs most commonly in school aged-children. The ill child typically has a "slapped cheek" rash on the face and a lacy red rash on the trunk and limbs. Occasionally, the rash may itch. An ill child may have a low-grade fever, malaise, or a "cold" a few days before the rash breaks out. The child is usually not very ill, and the rash resolves in 7 to 10 days.

# Historical Perspective
The fifth disease is also referred to as erythema infectiosum (meaning infectious redness) and as human parvovirus B19 Infection, slapped cheek syndrome, slap cheek, slap face or slapped face.  It is a mild rash illness that occurs most commonly in children.  The name "fifth disease" derives from its historical classification as the fifth of the classical childhood skin rashes or exanthems. In 1975, the cause of the Fifth disease was discovered to be parvovirus B19.

# Pathophysiology
A person infected with parvovirus B19 is contagious during the early part of the illness before the rash appears. By the time a child has the characteristic "slapped cheek"  of the fifth disease, for example, he or she is probably no longer contagious and may return to school or child care center. This contagious period is different than that for many other rash illnesses, such as measles, for which the child is contagious while he or she has the rash.
Parvovirus B19 has been found in the respiratory secretions (e.g., saliva, sputum, or nasal mucus) of infected persons before the onset of rash when they appear to "just have a cold." The virus is highly contagious and spreads from one person to another by direct contact with those secretions, such as sharing drinking cups or utensils. The virus can be acquired from blood products and can also be transmitted from mother to fetus through vertical transmission.
A susceptible person usually becomes ill 4 to 14 days after being infected with the virus, but may become ill for as long as 20 days after infection.

# Causes
Fifth disease is caused by infection with human parvovirus B19. Human parvovirus is a linear, non-segmented single-stranded DNA virus. Due to the lack of lipid envelope, the virus is resistant to inactivation physically with heat or detergents 

# Epidemiology and Demographics
Parvovirus infections are most common in children aged five to fifteen years and outbreaks can arise especially in nurseries and schools.
The infection occurs mostly in spring and later winter months.

# Risk Factors
Anyone can get a Fifth disease. Once anyone has had it, they become immunized against the virus. Because the virus is so common, most people acquire immunity in childhood. The disease is not very serious unless the person infected has conditions (problems with immune system, pregnancy, sickle-cell disease, anemia)

# Natural History, Complications and Prognosis
Fifth disease is usually a mild illness that resolves on its own among children and adults who are otherwise healthy. The complications following the infection include arthropathy (knees are most commonly involved in children). The virus targets rapidly growing erythroid progenitor cells hence, an aplastic crisis can be another complication. Occasionally, serious complications like hydrops fetalis may develop from parvovirus B19 infection during pregnancy.

# Diagnosis

## History and Symptoms
The first symptoms of the fifth disease are usually mild and nonspecific including fever, runny nose and headache, nausea followed by the development of a "slapped cheek" rash on the face associated with circumoral pallor later, followed by a lacy red rash on the trunk and limbs.

## Physical Examination

### Skin
Bright red cheeks are a defining symptom of the infection in children (hence the name "slapped cheek disease"). Occasionally the rash will extend over the bridge of the nose or around the mouth.  In addition to red cheeks, children often develop a red, lacy rash on the rest of the body, with the upper arms and legs being the most common locations.

## Laboratory Findings
A physician can often diagnose the fifth disease by seeing the typical rash during a physical examination. In cases in which it is important to confirm the diagnosis, a blood test may be done to look for antibodies to parvovirus. Antibodies are proteins produced by the immune system in response to parvovirus B19 and other germs. If an immunoglobulin M (IgM) antibody to parvovirus B19 is detected, the test result suggests that the person has had a recent infection.
The testing for viral DNA is only recommended in immunocompromised patients or the ones with the aplastic crisis.

# Treatment

## Medical Therapy
Treatment of the fifth disease is mainly symptomatic. Adults with joint pain and swelling may need to rest, restrict their activities, and take medicines such as aspirin or ibuprofen to relieve symptoms. Some patients with complications may also require transfusions or intravenous immune globulin therapy.

## Primary Prevention
There is no vaccine or medicine that prevents parvovirus B19 infection. Frequent handwashing is recommended as a practical and probably effective method to decrease the chance of becoming infected.