a brief presentation of the baltimore classification of virus under introduction to vriology. the presentation is by Theophilus A. Apraku

1. BALTIMORE
CLASSIFICATION OF VIRUS.

2. Presented by:

3.  This kind of viral classification was created by an
American Biologist named David Baltimore.
 It is basically based on the method of viral
synthesis.
 It groups viruses into families according to their
type of genome.
 As such there are seven groups of classification;
Groups I -VII

4.  They are double- stranded DNA viruses.
 These viruses enter the host’s nucleus before they
can replicate. (EXCEPTION: Poxvirus family)
 Again, they require the host’s polymerases to
replicate the viral genome.
 The virus may induce the cell to undergo cell division
which may lead to transformation of the cell.(leading
to cancer).
 Examples include Herpesviridae, Adenoviridae and
Papoviridae.

5.  They are Single-Stranded DNA viruses.
 Most of these viruses have circular genomes.
(exception is the Parvoviruses).
 Eukaryotic-infecting viruses replicate in the nucleus
via rolling circle mechanism, forming a double-
stranded DNA intermediate.
 Examples include;Anelloviridae, Circoviridae, and
parvoviridae (vertebrates); Geminiviridae and
Nanoviridae (plants), Microviridae (prokaryotes).

6.  They are Double-Stranded RNA viruses.
 They replicate in the core capsid in the cytoplasm.
 They do not have to use the host’s replication
polymerases.
 Replication is monocistronic and includes individual
segmented genome (each gene codes for one
protein).
 Examples include the Reoviridae and Birnaviridae.

7.  They are Single-Stranded RNA viruses-Positive sense
 Positive sense RNA viruses can be accessed directly by host
ribosome to form proteins.They are grouped into two.
 Viruses With Polycistronic mRNA: genome RNA form
mRNA which is translated into polyproteins; then cleaved
into proteins.
 Viruses with complex transcription. (subgenomic mRNA,
ribosomal frameshifting, and proteolytic processing of
polyproteins used).
 Examples of this class include the families Astrovirdae,
Caliciviridae,Coronovirdae, Flaviviridae,Picornaviridae,
Arteriviridae, andTogaviridae.

8.  They are Single-Stranded RNA viruses – Negative sense.
 Negative sense RNA viruses cannot be accessed directly by
Host’s ribosomes. Instead they must be transcribed into
readable forms.They are grouped into two.
 Viruses with non segmented genome: Negative stranded
genome is transcribed into monocistronic mRNA.
Replication occurs in the cytoplasm.
 Viruses with segmented genome: each genome segment
produces monocistronic mRNA. Replication occurs in the
nucleus.
 Examples include Arenaviridae, Orthomyxoviridae,
Paramyxoviridae, Bunyaviridae, Filoviridae.

9.  They are Postive-Sense Single Stranded RNA
viruses.They replicate through DNA
intermediates.
 These viruses use reverse transcriptase to convert
positive sense RNA to DNA.
 The DNA are spliced into host’s genome using
integrase and then replication commences.
 Example include Retroviruses.

10.  They are Double Stranded DNA viruses.
 They replicate through Single Stranded RNA
intermediates.
 DNA is filled in to form covalently closed circles.These
serve as templates for production of viral mRNA and
subgenomic RNA.
 The pregenome RNA serves as a template for viral
reverse transcriptase which produces DNA genome.
 Examples include Hepadnaviridae.

11. THANKYOU!!