Parvovirus B19 (B19 virus) was the first human parvovirus to be discovered, by chance in 1975 by the Australian virologist Yvonne Cossart. It gained is name because it was discovered in well B19 of a large series of petri dishes apparently numbered in this way.

Parovirus B19 is best known for causing a childhood exanthem called "fifth disease" (erythema infectiosum).

Virology

The B19 virus belongs to the Parvoviridae family of small DNA viruses. It is classified as Erythrovirus due to its capability to invade red blood cell precursors in the bone marrow.

Transmission

The virus is spread by infected respiratory droplets.

Epidemiology

A significant increase in the number of cases is seen every three to four years; the last epidemic year was 1998. Parvovirus B19 only causes an infection in humans; cat and dog parvoviruses do not infect humans. In contrast with small animals, there is no vaccine available for human parvovirus B19.

Role in disease

Fifth disease

After being infected, patients usually develop the illness after an incubation period of four to fourteen days. The disease commences with fever and malaise while the virus is most abundant in the bloodstream, and 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.

Arthritis

In adults (and perhaps some children), parvovirus B19 can lead to a seronegative arthritis which is easily controlled with analgesics. Possibly up to 15% of all new cases of arthritis are due to parvovirus, and a history of recent contact with a patient and positive serology generally confirms the diagnosis. The arthritis does not progress to other forms of arthritis.

Aplastic crisis

Although most patients have an arrest of erythropoiesis (production of red blood cells) during parvovirus infection, it causes problems in patients with sickle cell anemia, who are heavily dependant on erythropoeisis due to the reduced lifespan of the red cells. This is termed "aplastic crisis". It is treated with blood transfusion. Sickle-cell patients will probably be the first candidates to be candidates for a parvovirus B19 vaccine when this is developed.

Hydrops fetalis

Parvovirus infection in pregnant women is associated with hydrops fetalis due to severe fetal anemia, sometimes leading to spontaneous abortion.

Reference

• Young NS, Brown KE. Parvovirus B19. N Engl J Med 2004;350:586-97.
• Association of Medical Microbiologists page on parvovirus B19