Primate erythroparvovirus 1, generally referred to as B19 virus, parvovirus B19
or sometimes erythrovirus B19, was the first known human virus in the family
Parvoviridae, genus Erythroparvovirus; it measures only 23–26 nm in diameter.
The name is derived from Latin, parvum meaning small, reflecting the fact that
B19 ranks among the smallest DNA viruses. B19 virus is most known for
causing disease in the pediatric population; however, it can also affect
adults. It is the classic cause of the childhood rash called fifth disease or
erythema infectiosum, or "slapped cheek syndrome."
The virus was discovered by chance in 1975 by Australian virologist Yvonne
Cossart. It gained its name because it was discovered in well B19 of a large
series of microtiter plates labelled in this way.
Virology Erythroviruses belong to the
Parvoviridae family of small DNA viruses. It is a non-enveloped,
icosahedral virus that contains a single-stranded linear DNA genome.
Approximately equal proportions of DNA of positive and negative sense are found
in separate particles. At each end of the DNA molecule there are palindromic
sequences which form "hairpin" loops. The hairpin at the 3' end serves as a
primer for the DNA polymerase. It is classified as erythrovirus because of
its capability to invade red blood cell precursors in the bone marrow. Three
genotypes have been recognised. In humans the P antigen is the cellular
receptor for parvovirus B19 virus that causes Erythema infectiosum in children.
This infection is sometimes complicated by severe aplastic anemia caused by
lysis of early erythroid precursors. Transmission
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 contacts. Infectivity
Symptoms begin some six days after exposure and last about a week. Infected
patients with normal immune systems are contagious before becoming symptomatic,
but probably not after then. Individuals with B19 IgG antibodies are generally
considered immune to recurrent infection, but reinfection is possible
in a minority of cases. About half of adults are B19-immune due to a past
infection. Epidemiology
A significant increase in the number of cases is seen every three to four years;
the last epidemic year was 1998. Outbreaks can arise especially in
nurseries and schools. Parvovirus B19 causes an infection in
humans only. Cat and dog parvoviruses do not infect humans. There is no vaccine
available for human parvovirus B19, though attempts have been made to
develop one. Role in disease
= Fifth disease = Fifth disease or erythema infectiosum is
only one of several expressions of Parvovirus B19. The associated bright
red rash of the cheeks gives it the nickname "slapped cheek syndrome". Any
age may be affected, although it is most common in children aged six to ten
years. It is so named because it was the fifth most common cause of a pink-red
infection associated rash to be described by physicians .
Once infected, patients usually develop the illness after an incubation period
of four to fourteen days. The disease commences with high fever and malaise,
when the virus is most abundant in the bloodstream, and patients are usually no
longer infectious once the characteristic rash of this disease has
appeared. The following symptoms are characteristic:
A usual brief viral prodrome with fever, headache, nausea, diarrhea.
As the fever breaks, a red rash forms on the cheeks, with relative pallor around
the mouth, sparing the nasolabial folds, forehead, and mouth.
"Lace-like,(reticular)" red rash on trunk or extremities then follows the
facial rash. Infection in adults usually only involves the reticular rash, with
multiple joint pain predominating. Exacerbation of rash by sunlight, heat,
stress. Teenagers or young adults may develop
the so-called "Papular Purpuric Gloves and Socks Syndrome".
= AIDS = Parvovirus B19 is a cause of chronic
anemia in individuals who have AIDS. It is frequently overlooked. Treatment with
intravenous immunoglobulin usually resolves the anemia although relapse can
occur. The parvovirus infection may trigger an inflammatory reaction in AIDS
patients who have just begun antiretroviral therapy.
= Arthritis = In adults, 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 parvovirus
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.
= Aplastic crisis = Although most patients have a decrease
of erythropoiesis during parvovirus infection, it is most dangerous in
patients with pre-existing bone marrow stress, for example sickle cell anemia
or hereditary spherocytosis, and are therefore heavily dependent on
erythropoiesis due to the reduced lifespan of the red cells. This is
termed "aplastic crisis". It is treated with blood transfusion.
= Hydrops fetalis = 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, but minimal after then. Routine
screening of the antenatal sample would enable the pregnant mother to determine
the risk of infection. Knowledge of her status would allow the mother to avoid
contact with individuals suspected or known to have an ongoing infection,
however, at the present time, antenatal testing for immunity is not recommended,
since there is no good means to prevent the infection, there is not specific
therapy and there are no vaccines available. It may increase maternal
anxiety and fear without proven benefit. The best approach would be to recommend
all pregnant women to avoid contact with children with current symptoms of
infection, as described above. The risk to the fetus will be reduced with
correct diagnosis of the anemia and treatment. There is some evidence that
intrauterine Parvovirus B19 infection leads to developmental abnormalities in
childhood. Treatment
At the moment, there are no treatments that directly target Parvovirus B19
virus. Intravenous immunoglobulin therapy therapy has been a popular
alternative because doctors can administer it without stopping
chemotherapy drugs like MEL-ASCT. Also, the treatment's side effects are rare as
only 4 out of 133 patients had complications even though 69 of the
patients had organ transplants and 39 of them were HIV positive. This is a large
improvement over administering Rituximab. The monoclonal antibody
against the CD20 protein has been shown to cause acute hepatitis, neutropenia
via Parvovirus B19 reactivations, and even persistent Parvovirus B19
infection. However, it is important to note that IVIG therapy is not perfect as
34% of treated patients will have a relapse after 4 months.
See also Human bocavirus
Erythema infectiosum References
External links Parvovirus B19 Information
fifthdisease.org