The document provides a comprehensive overview of viruses, detailing their characteristics, classification criteria based on nucleic acid type, replication methods, and host range. It explains the morphology of viruses, describing them as either rod-shaped or spherical, and outlines laboratory diagnosis methods for viral infections. Additionally, the nomenclature of viruses is discussed, including naming conventions related to diseases, geographical locations, and host organisms.

1. VIRUSES
DR.PRINCE C P
Associate Professor , Department of Microbiology,
Mother Theresa Post Graduate & Research Institute of Health Sciences
(Government of Puducherry Institution)

2. General characters of Viruses
• Small size (20-300 nm) / bacteria (size measured in μm)
• Viral genome – single type of nucleic acid:
• DNA – dezoxyriboviruses
• RNA - riboviruses
• Totally dependant on living cells for all metabolic processes
• May infect humans, animals, plants, bacteria, fungi,parasites, insects
• Virion = viral corpuscle = elementary, infectious unit

3. • Only visible by electron microscopy

4. Criteria for Classification of virus
• Type and structure of their nucleic acids
• Methods of replication
• Host range
• Chemical and physical characteristics

5. Symmetry of viruses
 Viruses are divided into three groups, based on the
morphology of the nucleocapsid and the arrangement
of capsomeres.
 • Two primary shapes of virus is rod and spherical.
 • Rod shaped virus-helical symmetry
 • Spherical virus-icosahedron

7. Laboratory diagnosis of viral infections
Methods:
• Cytology
• Electron microscopy
• Cultivation
• Detection of viral proteins
• Serology
• Molecular diagnosis (detection of
genetic material i.e. nucleic acids)

26. Nomenclature of Viruses
 1. Named after the diseases eg. Measles virus, smallpox virus
 2. Name after the places where the disease first reported eg. Newcastle
disease virus, Ebola virus, Norwalk virus, Bunyaviridae
 3. Host and signs of disease eg. Tobacco mosaic virus, cauliflower mosaic
virus, brome mosaic virus

27. Classification of virus
 determined by the structural and chemical composition of virus
 apply to all plant viruses, animal viruses and bacterial viruses
 Virus is acellular cell – cannot be categorised using taxonomic
classification
 International Committee on taxonomy of Viruses (ICTV) to classify the
viruses

28. Criteria for Classification of virus
 Type and structure of their nucleic acids
 Methods of replication
 Host range
 Chemical and physical characteristics

29. Arrangement of capsomers in the virus
Symmetry of viruses
 Viruses are divided into three groups, based on the
morphology of the nucleocapsid and the arrangement
of capsomeres.
 • Two primary shapes of virus is rod and spherical.
 • Rod shaped virus-helical symmetry
 • Spherical virus-icosahedron

30. Cubic symmetry

31. Helical symmetry

34. Thank You