Classification of Viruses

For our 1^st lecture of the semester we learnt about the Classification of Viruses! It was quite interesting to gain more insights of how the World of Virology works. But we guess it will mean more memory work for the coming exams!

So we classified what we learnt today into 3 groups:

A. Virus taxonomy

B. Lwoff’s Classification

C. Baltimore's Classification

Taxonomy and Classification is a mean to classify and identify living things.

There are 8 main taxonomic ranks: domain, kingdom, phylum, class, order, family, genus, species, and it gets more specific as it goes down the row.

The lecturer told us an easy and fun way to memorise this table!

Keep Plates Clean Or Family Gets Sick

Picture courtesy of flickr.com/photos/

Classification of Viruses

Morphology: Viruses are grouped on the basis of size and shape, chemical composition and structure of the genome, and mode of replication.

Chemical Composition and Mode of Replication: The genome of a virus may consist of DNA or RNA, which may be single stranded(ss) or double stranded(ds), linear or circular.

Hmm.. So how did the classification of viruses come about?

A. Virus Taxonomy-ICTV

International Committee on Taxonomy of Viruses

Taxonomy lies at the uneasy interface between biology and logic. The processing of information follows somewhat different rules in these two systems and the role of taxonomy is to reconcile them as tidily as possible. To thisend, the International Union of MicrobiologicalSocieties (IUMS) charged the International Committee onTaxonomy of Viruses (ICTV) with the task of developing,refining, and maintaining a universal virus taxonomy. The goal of this undertaking is tocategorize the multitude of known viruses into a single classification scheme that reflects their evolutionaryrelationships.

B. Lwoff's classification

In 1962 Lwoff, R. W. Horne, and P. Tournier advanced a comprehensive scheme for the classification of all viruses consisting of phylum - class - order - family - subfamily - genus -species - strain/type. Four main characteristics are used:

1. Nature of the nucleic acid:RNA or DNA

2. Symmetry of the capsid

3. Presence or absence of an envelope

4. Dimensions of the virion and capsid

C. Baltimore's Classification

The Baltimore classification is based on genetic contents and replication strategies of viruses.

According to Baltimore classification, viruses are divided into the following 7 classes:

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1.dsDNA viruses

2.ssDNA viruses

3.dsRNA viruses

4.(+)-sense ssRNA viruses

5.(-)-sense ssRNA viruses

6.RNA reverse transcribing viruses

7.DNA reverse transcribing viruses