Page 95 - MNU microbiology theoritical 2025

General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025

Classification of Viruses

1- ICTV classification

The International Committee on Taxonomy of Viruses developed the current

classification system.

• Viruses with similar structural, genomic & replication properties are grouped

into families (suffix: viridae) e.g. Herpesviridae, Retroviridae.

• Families subdivided into genera (suffix:virus) e.g. Herpesvirus.

• Genera is subdivided into species. Common names are used for species e.g.

Herpes simplex virus, Humman immunodeficiency virus

• Subspecies based on nucleotide sequence and antigenic reactivities are

designated by a number e.g. Herpes simplex virus type 1, Herpes simplex virus

type 2, HIV-1, HIV-2

2- Classification based on the presence of nucleic acid
DNA virus
• There are two different types of DNA virus

- Single-stranded (ss) DNA virus: e.g. Picornaviruses, Parvovirus, etc.
- Double-stranded (ds) DNA virus: e.g. Adenovirus, Herpes virus, etc.

RNA virus
• There are two different types of RNA virus

- Double-stranded (ds) RNA virus: e.g. Reovirus, etc.

- Single-stranded (ss) RNA virus. It is further classified into two Positive

sense RNA (+RNA) and negative sense RNA (-RNA).

Rabies virus, Influenza virus are examples of single-stranded RNA virus.

General Microbiology & Immunology (PM 401) theoretical handbook Page 84