Fifth disease

Fifth disease, also known as erythema infectiosum and slapped cheek syndrome, is a common and contagious disease caused by infection with parvovirus B19. This virus was discovered in 1975 and can also cause other diseases besides fifth disease. Fifth disease typically presents as a rash and is most common in children. Parvovirus B19 can affect people of all ages; about two out of ten persons infected will have no symptoms.

Parvovirus B19 is the only virus within the Parvoviridae family to cause disease in humans, especially in children. The most common disease derived from parvovirus B19 is fifth disease. This disease is spread in close contact through respiratory droplets, which can be from the nose, mouth, or direct contact with an infected person. Fifth disease is most commonly spread in the winter and spring seasons in children aged six to fourteen years old. Parvovirus B19 will start replicating from anywhere for four to eighteen days. Infected children will be most contagious during this time and before they develop the most notable sign, a red rash on their cheeks, and other symptoms.

Since parvovirus B19 is a single stranded DNA virus, replication can only occur in dividing cells. This is also why other populations besides children can become infected with parvovirus B19, develop fifth disease, and have complications. Certain populations are at a higher risk if they have more dividing cells or a weakened immune system than the typical person. These populations include pregnant women, fetuses, adults, and immunocompromised. Over the last few years, first-time infections in pregnant women have been increasing throughout the world. About 1-5% of pregnant women can become infected. Typically, having the virus will not impact the outcome of the pregnancy, and 90% of cases of infected fetuses do not lead to any serious outcomes. However, complications can still occur in both the fetus and mother. For example, if fetuses contract parvovirus B19, possible complications can include miscarriage or intrauterine fetal death. Additionally, infected adults have been documented to develop arthralgias, or joint pain. Also, a specific group of immunocompromised people with bone marrow failure and infected with parvovirus B19 have been shown to develop aplastic crisis. Other notable complications caused by infection from parvovirus B19 can include gloves and sock syndrome.

The symptoms of fifth disease are usually mild and may start as a fever, headache or a runny nose.^{[citation needed]} These symptoms pass, then a few days later, the rash appears. The bright red rash most commonly appears in the face, particularly the cheeks. Children infected typically go through 3 stages; first when the rash appears on the face. This is a defining symptom of the infection in children (hence the name "slapped cheek disease"). In addition to red cheeks, the second stage consists of children developing a red, lacy rash on the rest of the body, with the upper arms, torso, and legs being the most common locations. The rash typically lasts a few days and may itch; some cases have been known to last for several weeks. People are usually no longer infectious once the rash has appeared. Lastly the third stage consists of recurring rashes due to hot showers, sun exposure, or minor injuries lasting about 11 days.

In children, the risk of Parvovirus B19-related arthralgia (joint-stiffness) is less than 10%, but 19% of those with new-onset arthritis may have developed the B19 infection within the previous 10 weeks. Teenagers and adults may present with joint pain or swelling, out of which 60% infected females and 30% of infected males reported these symptoms. Out of these, 20% of the females may experience continuous joint stiffness for several months or years. Symptoms can persist up to 3 weeks since onset. Sometimes, fifth disease can also cause serious complications, especially if the person is pregnant, has anemia, or is immunocompromised; affecting the blood system, joints or nerves. Adults with fifth disease may have difficulty in walking and in bending joints such as wrists, knees, ankles, fingers, and shoulders.

The disease is usually mild, but in certain risk groups and rare circumstances, it can have serious consequences:

Fifth disease, also known as erythema infectiosum, is caused by parvovirus B19, which only infects humans. Infection by parvovirus B19 can lead to multiple clinical manifestations, but the most common is fifth disease.

Parvovirus B19 (B19V) is a small, single-stranded, non-enveloped DNA virus. Binding of B19V capsid to the cellular receptor globoside (Gb4Cer) results in a cascade of structural changes and subsequent signal transduction processes facilitating the entry of parvovirus B19 into the host cell. After gaining access to the host cell, B19V binds to glycosphingolipid globoside (blood group P antigen) targeting erythroid lineage in the bone marrow. Replication of viral genome and release of virus from infected cells lead to various complex effects on host's cellular environment such as induction of DNA damage, hijack of cell cycle and apoptosis (killing of infected cells).