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The B19 virus, generally referred to as parvovirus B19[1] or sometimes erythrovirus B19[2], was the first (and until 2005 the only) known human virus in the family of parvoviruses, genus erythrovirus. B19 virus causes a childhood rash called fifth disease or erythema infectiosum which is commonly called slapped cheek syndrome.[3]
The virus was discovered by chance in 1975 by Australian virologist Yvonne Cossart.[4] It gained its name because it was discovered in well B19 of a large series of petri dishes apparently numbered in this way.[5]
Erythroviruses belong to the Parvoviridae family of small DNA viruses.[6] 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. [7] 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.[8] The secondary attack risk for exposed household persons is about 50%, and about half of that for classroom contacts.[9]
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.[10] Individuals with B19 IgG antibodies are generally considered immune to recurrent infection, but reinfection is possible in a minority of cases.[11] About half of adults are B19-immune due to a past infection.
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.
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