During the distributed classroom sessions (November-December 2011) we got a lot of interesting questions from students attending the sessions. We would like to share a few of these questions with more elaborate answers with you. Pushan asked-

Are there any types of viruses?

We can express this question technically as how are viruses classified?

ANSWER: There are various classification systems for viruses. There are different classification systems for viruses based on their morphology, genetic material, host organisms and type of disease they cause.

Let us start with the simplest one. You know that viruses are parasites. So the simplest classification is to classify them on the basis of hosts they infect! According to this classification, viruses can be divided into three types-

  1. Animal viruses (Viruses which infect animals)
  2. Plant viruses (Viruses which infect plants)
  3. Bacteriophages (Viruses which infect bacteria)

Another classification system of viruses is based on the genetic material they contain. This is known as Baltimore System. The three categories in this system are-

  1. DNA viruses
  2. RNA viruses
  3. Retroviruses (Reverse transcribing viruses)

These are just broad categories which are further divided into subcategories.

Further Questions:

  • Do you know other systems of classifying viruses?
  • Can you classify viruses you know using the two classification systems given above?
  • List down characters of viruses and think how these characters can be used to classify them.