Rabu, 19 Oktober 2011

Virus Famili Parvoviridae

The Parvoviridae family includes the smallest known viruses, and some of the most environmentally resistant. They were discovered during the 1960s and affect vertebrates and insects. Parvoviridae have a genome consisting of single-stranded DNA and an icosahedral capsid.

Parvovirus B19 was the first human parvovirus to be discovered and is best known for causing a childhood exanthem called "fifth disease" (erythema infectiosum), although it is also associated with other diseases including arthritis.

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.

Virology
The viruses in this family are small (18-26 nanometers in diameter) and non enveloped. The viron is isosahedral with triangulation number (T) = 1. There are 60 copies of the coat protein in the viron.

The genome is 4-6 kilobases in length and usually encodes two open reading frames. The 5' open reading frame encodes two nonstructural proteins (NS-1 and NS-2) and the 3' open reading frame encodes two or three capsid proteins (VP1, VP2, VP3). Both the 5' and 3' termini have hairpin loops. In the genus Bocavirus there is a third open reading frame between the non structural and structural open reading frames.

The NS-1 protein has a superfamily 3 DNA helicase motif. These motifs are common in DNA viruses. The proteins that contain these motifs bind to the origin of replication and unwind the viral genome allowing access by the host's proteins to the viral genome for replication and transcription.

The genome is replicated by a unique rolling hairpin mechanism.

Taxonomy
The family is divided into two subfamilies - Parvovirinae - which infect vertebrates and - Densovirinae - which infect invertebrates. Each subfamily has been subdivided into several genera. The classification of the subfamily Parvovirinae may need revision.

Subfamily Parvovirinae:

    Genus Amdovirus; type species: Aleutian mink disease virus
    Genus Bocavirus; type species: Bovine parvovirus
    Genus Dependovirus; type species: Adeno-associated virus 2
    Genus Erythrovirus; type species: B19 virus
    Genus Partetravirus;
    Genus Parvovirus; type species: Murine minute virus

Subfamily Densovirinae:
Genus Brevidensovirus; type species: Aedes aegypti densovirus
Genus Densovirus; type species: Junonia coenia densovirus
Genus Iteravirus; type species: Bombyx mori densovirus
Genus Pefudensovirus; type species: Periplanta fuliginosa densovirus

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