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Baltimore Classification

Baltimore Classification

Aleksandrs Cudars

March 25, 2013
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  1. View Slide

  2. The Baltimore
    classification, developed
    by David Baltimore, is a
    virus classification
    system that groups
    viruses into families,
    depending on their type
    of genome (DNA, RNA,
    single-stranded (ss),
    double-stranded (ds),
    etc.) and their method of
    replication.

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  3. Classifying viruses according to their genome
    means that those in a given category will all
    behave in much the same way, which offers
    some indication of how to proceed with further
    research
    CLASSIFICATIONS

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  4. I: dsDNA viruses
    CLASSIFICATIONS

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  5. I: dsDNA viruses (e.g. Adenoviruses,
    Herpesviruses, Poxviruses)
    CLASSIFICATIONS
    Genome organization within this
    group varies considerably. Some have
    circular genomes (Baculoviridae,
    Papovaviridae and Polydnaviridae)
    while others have linear genomes
    (Adenoviridae, Herpesviridae and
    some phages). Some families have
    circularly permuted linear genomes
    (phage T4 and some Iridoviridae).
    Others have linear genomes with
    covalently closed ends (Poxviridae
    and Phycodnaviridae).

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  6. I: dsDNA viruses
    CLASSIFICATIONS
    Most have head-tail
    morphologies and
    linear double-
    stranded DNA
    genomes. Other
    morphologies have
    also been described:
    spindle shaped, rod
    shaped, filamentous,
    icosahedral and
    spherical. Additional
    morphological types
    may exist.

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  7. II: ssDNA viruses
    CLASSIFICATIONS

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  8. II: ssDNA viruses
    CLASSIFICATIONS
    All viruses in this group
    require formation of a
    replicative form – a double
    stranded DNA intermediate –
    for genome replication. This
    is normally created from the
    viral DNA with the assistance
    of the host's own DNA
    polymerase.

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  9. II: ssDNA viruses
    CLASSIFICATIONS
    A division of the circular single
    stranded viruses into four types
    has been proposed. This division
    seems likely reflects their
    phylogenetic relationships.
    Type I genomes are characterized
    by a small circular DNA genome
    (approximately 2-kb), with the Rep
    protein and the major open
    reading frame (ORF) in opposite
    orientations. This type is
    characteristic of the circoviruses,
    geminiviruses and nanoviruses.

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  10. II: ssDNA viruses (+ strand or "sense") DNA (e.g.
    Parvoviruses)
    CLASSIFICATIONS
    Type III genomes contain
    two major ORFs in the
    same orientation. This
    arrangement is typical of
    the anelloviruses.
    Type II genomes have the unique feature of two separate Rep ORFs.
    Type IV genomes have the largest genomes of nearly 4-kb, with up to eight
    ORFs. This type of genome is found in the Inoviridae and the Microviridae.
    Given the variety of single stranded viruses that have been described this
    scheme – if it is accepted by the ICTV – will need to be extended.

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  11. III: dsRNA viruses
    CLASSIFICATIONS

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  12. III: dsRNA viruses
    CLASSIFICATIONS
    Double-stranded (ds) RNA
    viruses are a diverse group
    of viruses that vary widely
    in host range (humans,
    animals, plants, fungi, and
    bacteria), genome
    segment number (one to
    twelve) and virion
    organization (T-number,
    capsid layers or turrets).

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  13. III: dsRNA viruses
    CLASSIFICATIONS
    Members of this group include the rotaviruses, known globally
    as a common cause of gastroenteritis in young children, and
    bluetongue virus, an economically important pathogen of
    cattle and sheep.

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  14. III: dsRNA viruses
    CLASSIFICATIONS
    Of these families, the Reoviridae is the largest and most diverse in
    terms of host range.

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  15. IV: (+)ssRNA viruses
    CLASSIFICATIONS

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  16. IV: (+)ssRNA viruses
    CLASSIFICATIONS
    An RNA virus is a virus that has RNA (ribonucleic acid) as its genetic material.
    This nucleic acid is usually single-stranded RNA (ssRNA), but may be double-
    stranded RNA (dsRNA).
    Notable human diseases caused by RNA viruses include SARS, influenza,
    hepatitis C, West Nile fever, polio and measles.

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  17. IV: (+)ssRNA viruses
    CLASSIFICATIONS
    The proposed classification of positive strand RNA viruses is based on the
    RNA dependent RNA polymerase. Three groups have been recognised:
    I. The picorna like group (Picornavirata)
    II. The flavi like group (Flavivirata)
    III. The alpha like group (Rubivirata)

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  18. V: (−)ssRNA viruse
    CLASSIFICATIONS

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  19. V: (−)ssRNA viruses (− strand or antisense) RNA
    (e.g. Orthomyxoviruses, Rhabdoviruses)
    CLASSIFICATIONS
    Negative-sense ssRNA viruses must have their
    genome copied by an RNA-dependent RNA
    polymerase to form positive-sense RNA. This
    means that the virus must bring along with it the
    RNA replicase enzyme. The positive-sense RNA
    molecule then acts as viral mRNA, which is
    translated into proteins by the host ribosomes.
    The resultant protein goes on to direct the
    synthesis of new virions, such as capsid proteins
    and RNA replicase, which is used to produce new
    negative-sense RNA molecules.

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  20. VI: ssRNA-RT viruses
    CLASSIFICATIONS

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  21. VI: ssRNA-RT viruses (+ strand or sense) RNA
    with DNA intermediate in life-cycle (e.g.
    Retroviruses)
    CLASSIFICATIONS

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  22. VI: ssRNA-RT viruses
    CLASSIFICATIONS
    A retrovirus is an RNA virus that
    replicates in a host cell. First it uses
    its own reverse transcriptase enzyme
    to produce DNA from its RNA
    genome, reverse of the usual
    pattern, thus retro (backwards). This
    new DNA is then incorporated into
    the host's genome by an integrase
    enzyme. The cell then treats the viral
    DNA as part of its own instructions,
    which it follows blindly, making the
    proteins required to assemble new
    copies of the virus.

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  23. VII: dsDNA-RT viruses
    CLASSIFICATIONS

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  24. VII: dsDNA-RT viruses
    CLASSIFICATIONS
    DsDNA-RT viruses are not considered
    as DNA viruses (class I of Baltimore
    classification), but rather reverse
    transcribing viruses because they
    replicate through an RNA
    intermediate.
    It includes Hepadnaviridae and
    Caulimoviridae.
    The term "pararetrovirus" is also
    used for this group.

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  25. View Slide

  26. References
    • http://en.wikipedia.org/wiki/Baltimore_classification
    • http://en.wikipedia.org/wiki/David_Baltimore
    • http://ian.umces.edu/imagelibrary/albums/userpics/12865/normal_ian-symbol-adenovirus.png
    • http://static.lolyard.com/lol/retrovirus.jpg
    • http://www.virobathe.org/M055290-Adenovirus,_TEM-SPL.jpg
    • http://eonreality.serveraddress.com/Content/2813/Image1.jpg
    • http://www.microbiologybytes.com/virology/3035pics/KSHV.jpg
    • http://www.visualphotos.com/photo/1x3745975/t2_bacteriophage_color_enhanced_transmission_electron_micrograph_tem_of_t2_bacteriophages_invad_BA2175.jpg
    • http://en.wikipedia.org/wiki/SsDNA_virus
    • http://3.bp.blogspot.com/-PrrPNdKCKO4/UI3f5ejT-3I/AAAAAAAAEMM/3_BBQM7O2C4/s1600/PlagueIncNanovirus.jpg
    • http://ictvdb.bio-mirror.cn/WIntkey/Images/em_anell_2.jpg
    • http://trialx.com/g/Parvovirus-5.jpg
    • http://www.virology.wisc.edu/virusworld/images/polyoma_1sid_qm.jpg
    • http://topnews.ae/images/Reoviruses.gif
    • http://www.virology.wisc.edu/virusworld/PS10/vp7-recoated_rotavirus_DLP_vmd01.jpg
    • http://www.reoviridae.org/dsRNA_virus_proteins/Aquareovirus%20particle.gif
    • http://3dciencia.com/blog/wp-content/uploads/2011/05/FAMD-foot-and-mouth-disease-virus-particle-fiebre-aftosa-glosopeda-picornavirus-Aphthovirus.jpg
    • http://en.wikipedia.org/wiki/DsRNA_virus
    • http://en.wikipedia.org/wiki/Positive-sense_ssRNA_virus
    • http://www.independent.co.uk/incoming/article8501795.ece/ALTERNATES/w460/web-sars.jpg
    • http://www.microbeworld.org//components/com_jlibrary/upload/thumbnail/802eb7fba1994d78ad7baa3497b64ea6.jpg
    • http://www.thetimes.co.uk/tto/multimedia/archive/00393/123643286__393023c.jpg
    • http://preview.turbosquid.com/Preview/2011/10/22__15_59_17/wire.jpgc9e404fa-c297-4c92-bdcc-02d2b1cd0c99Large.jpg
    • http://images.fineartamerica.com/images-medium-large/rabies-virus-2-russell-kightley.jpg
    • http://en.wikipedia.org/wiki/SsRNA-RT_virus
    • https://upload.wikimedia.org/wikipedia/commons/7/7e/Ms2capsid_surface.png
    • http://preview.turbosquid.com/Preview/2011/12/15__07_05_31/flu%20-%20orthomyxovirus.jpgf77386fa-2675-4b9e-a7af-f27431fbb36cLarge.jpg
    • http://en.wikipedia.org/wiki/DsDNA-RT_virus
    • http://www.stanford.edu/group/virus/hepadna/2004tansilvis/hepb.jpg
    • http://www.virology.net/big_virology/EM/virus2.jpg

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