Parvovirus B19

Taxobox | color=violet

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image_caption =Electron micrograph of Parvoviruses in blood
name = "Parvovirus B19"
virus_group = ii
familia = "Parvoviridae"
genus = Erythrovirus
species = Parvovirus B19

Parvovirus B19 ("B19 virus") was the first (and until 2005 the only) known human parvovirus. It was discovered by chance in 1975 by Australian virologist Yvonne Cossart.cite journal |author=Heegaard ED, Brown KE |title=Human parvovirus B19 |journal=Clin. Microbiol. Rev. |volume=15 |issue=3 |pages=485–505 |year=2002 |pmid=12097253 |doi=10.1128/CMR.15.3.485-505.2002|url=http://cmr.asm.org/cgi/pmidlookup?view=long&pmid=12097253] It gained its name because it was discovered in well B19 of a large series of petri dishes apparently numbered in this way.cite journal | author=Cossart YE, Field AM, Cant B, Widdows D | title=Parvovirus-like particles in human sera | journal=Lancet | year=1975 | pages=72–3 | volume=1 | issue=7898 | pmid = 46024 | doi=10.1016/S0140-6736(75)91074-0]

Parvovirus B19 is best known for causing a childhood exanthem called "fifth disease" or "erythema infectiosum".cite journal | author=Vafaie J, Schwartz RA | title=Parvovirus B19 infections | journal=Int J Dermatol | year=2004 | pages=747–9 | volume=43 | issue=10 | pmid = 15485533 | doi=10.1111/j.1365-4632.2004.02413.x]

Virology

The "B19 virus" belongs to the Parvoviridae family of small DNA viruses.cite journal | author=Brown KE | title=Variants of B19 | journal=Dev Biol (Basel) | year=2004 | pages=71–7 | volume=118 | pmid=15645675] It has a non-enveloped icosahedral nucleocapsid 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. [G. Siegl and P. Cassinotti, "Parvoviruses" Chapter 14, Topley and Wison's Microbiology and Microbial Infections, Vol. 1, Virology, 1998 pp. 261-280] It is classified as Erythrovirus because of its capability to invade red blood cell precursors in the bone marrow.

Transmission

The virus is primarily spread by infected respiratory droplets; blood-borne transmission, however, has been reported.cite book | author = Pattison JR, Patou G| title = Parvoviruses. "In:" Barron's Medical Microbiology "(Barron S "et al", eds.)| edition = 4th ed. | publisher = Univ of Texas Medical Branch | year = 1996 | id = ISBN 0-9631172-1-1 ] The secondary attack risk for exposed household persons is about 50%, and about half of that for classroom contacts.cite journal | author=Young NS, Brown KE | title=Parvovirus B19 | journal=N Engl J Med | year=2004 | pages=586–97 | volume=350 | issue=6 | pmid = 14762186 | doi=10.1056/NEJMra030840]

Infectivity

B19 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.cite journal | author=Corcoran A, Doyle S | title=Advances in the biology, diagnosis and host-pathogen interactions of parvovirus B19 | journal=J Med Microbiol | year=2004 | pages=459–75 | volume=53 | issue=Pt 6 | pmid=15150324 | doi=10.1099/jmm.0.05485-0] Individuals with B19 IgG antibodies are generally considered immune to recurrent infection, but reinfection is possible in a minority of cases.cite journal | author=Lehmann HW, von Landenberg P, Modrow S | title=Parvovirus B19 infection and autoimmune disease | journal=Autoimmun Rev | year=2003 | pages=218–23 | volume=2 | issue=4 | pmid = 12848949 | doi=10.1016/S1568-9972(03)00014-4] 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. In contrast with small animals, there is no vaccine available for human parvovirus B19.

Role in disease

Fifth disease

Fifth disease or "erythema infectiosium" is only one of several expressions of Parvovirus B19. Any age may be affected, although it is most common in children aged six to ten years.

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.

Teenagers or young adults tend to develop the so called 'Papular Purpuric Gloves and Socks Syndrome.' Unlike young children, these patients may be infectious with this rash.

Rash

The rash of fifth disease is typically described as "slapped cheeks," with erythema across the cheeks and sparing the nasolabial folds, forehead, and mouth. Because of this rash, fifth disease is sometimes called [http://www.fifthdisease.org/general.html slapped cheek syndrome] . Fifth disease is also known for "lace-like" rashes on the arms, legs, torso, and back. These rashes can last for up to 5 weeks and are worse after sun exposure, exercise, or hot baths.

Arthritis

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.

Aplastic crisis

Although most patients have an arrest of erythropoiesis (production of red blood cells) during parvovirus infection, it is most dangerous in patients who have sickle cell anemia or hereditary spherocytosis, and are therefore heavily dependent on erythropoeisis due to the reduced lifespan of the red cells. This is termed "aplastic crisis" (also called reticulocytopenia). It is treated with blood transfusion. Due to their increased susceptibility, Sickle-cell patients will be prime candidates for a parvovirus B19 vaccine when it is developed.

Hydrops fetalis

Parvovirus infection in pregnant women is associated with hydrops fetalis due to severe fetal anemia, sometimes leading to miscarriage or stillbirth.cite journal
author=Ergaz Z, Ornoy A
title=Parvovirus B19 in pregnancy
journal=Reprod. Toxicol.
volume=21
issue=4
pages=421–35
year=2006
pmid=16580942
doi=10.1016/j.reprotox.2005.01.006
url=http://linkinghub.elsevier.com/retrieve/pii/S0890-6238(05)00025-0] The risk of fetal loss is about 10% if infection occurs before pregnancy week 20 (esp. between weeks 14-20), 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 the risk of infection.The risk to the fetus will be reduced with correct diagnosis of the anemia (by ultrasound scans) and treatment (by blood transfusions). There is no evidence to suggest that Parvovirus B19 leads to developmental abnormalities in childhood.

References

External links

* [http://www.biotrin.com/ParvovirusB19.FifthDisease.HTML Parvovirus B19 Information]
* [http://www.fifthdisease.org/general.html fifthdisease.org]