Parvovirus B19 (B19 virus) was the first (and, until 2005, only) human parvovirus to be discovered, by chance in 1975
by the Australian virologist Yvonne Cossart. It gained its name because it was discovered in well B19 of a large series
of petri dishes apparently numbered in this way.
Parvovirus B19 is best known for causing a childhood exanthem called fifth disease or erythema infectiosum.
The B19 virus belongs to the Parvoviridae family of small DNA viruses. It is classified as Erythrovirus because of its
capability to invade red blood cell precursors in the bone marrow.
The virus is primarily spread by infected respiratory droplets; blood-borne transmission, however, has been reported.
The secondary attack risk for exposed household persons is about 50%, and about half of that for classroom
Fifth disease is also referred to as erythema infectiosum (meaning infectious redness) and as slapped cheek
syndrome, slap face or slapped face.
In 1975 its cause was discovered to be Parvovirus B19.
The bright red cheeks are a defining symptom of the infection in children (hence the name "slapped cheek disease"),
but the rash will not extend over the bridge of the nose or around the mouth. In addition to the 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.
Teenagers and adults may present with a self-limited arthritis.
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.
The disease is usually mild, but it does have the ability to cause some serious problems: it is associated with
spontaneous abortion in pregnant women, and with transient aplastic crisis in persons with chronic hemolytic anemia.
Primary infection in the first trimester has been linked to hydrops fetalis. The rash can last a couple of weeks and may
The name fifth disease stems from the fact that when diseases causing childhood exanthemata (rashes) were
enumerated, it was the fifth listed.
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.
In adults (and perhaps some children), parvovirus B19 can lead to a seronegative arthritis which is usually easily
controlled with analgesics. Women are approximately twice as likely as men to experience arthritis after parvo virus
infection. 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. This arthritis does not progress to other forms of
arthritis. Typically joint symptoms last 1-3 weeks, but in 10-20% of those affected, it may last weeks to months.
Parvovirus RA-1 had originally also been associated with rheumatoid arthritis, but this is now thought to have been an
error due to laboratory contamination.
Although most patients have an arrest of erythropoiesis (production of red blood cells) during parvovirus infection, it
causes worse problems in patients with sickle cell anemia, or with hereditary spherocytosis, who are heavily dependent
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 for a parvovirus B19 vaccine when it is developed.
Parvovirus infection in pregnant women is associated with hydrops fetalis due to severe fetal anemia, sometimes leading
to miscarriage or stillbirth. The risk of fetal loss is about 10% if infection occurs before pregnancy week 20 (esp.
between weeks 14-20), but minimal after then. This risk may be reduced with correct diagnosis of the anemia (by
ultrasound scans) and treatment (by blood transfusions). Once the baby is born, there is evidence to suggest no
developmental abnormalities due to B19 infection during pregnancy.
Parvoviruses can cause disease in some animals. Because the viruses require actively reproducing cells in order to
replicate, the type of tissue infected varies by the age of the animal. The gastrointestinal tract and lymphatic system can
be affected at any age, leading to vomiting, diarrhea and immunosuppression, but cerebellar hypoplasia is only seen in
cats that were infected in the womb or at less than two weeks of age, and disease of the myocardium is seen in puppies
infected between the ages of three and eight weeks. 
Canine parvovirus is a particularly deadly disease among young puppies, causing gastrointestinal tract damage and
dehydration as well as a cardiac syndrome in very young pups. It is spread by contact with an infected dog's feces.
Symptoms include lethargy, severe diarrhea, fever, vomiting, loss of appetite, and dehydration. Mouse parvovirus 1,
however, causes no symptoms but can contaminate immunology experiments in biological research laboratories.
Porcine parvovirus causes a reproductive disease in swine known as SMEDI, which stands for stillbirth, mummification,
embryonic death, and infertility. Feline panleukopenia is common in kittens and causes fever, low white blood cell count,
diarrhea, and death. Infection of the cat fetus and kittens less than two weeks old causes cerebellar hypoplasia. Mink
enteritis virus is similar in effect to feline panleukopenia, except that it does not cause cerebellar hypoplasia. A different
parvovirus causes Aleutian disease in minks and other mustelids, characterized by lymphadenopathy, splenomegaly,
glomerulonephritis, anemia, and death. The most accurate diagnosis of parvovirus is by ELISA. Dogs and cats can be
vaccinated against parvovirus.
Parvovirus B19, which causes fifth disease in humans, is a member of the Erythrovirus genus of Parvoviridae rather