Lecture 11: Classification and Replication of Viruses PDF

BIOL121: Impact of Microbes Classification and replication of viruses Prof Muhammad Munir [email protected]...

BIOL121: Impact of Microbes Classification and replication of viruses Prof Muhammad Munir [email protected] Furness Building, Office B05 07585184915 @VirologistMunir Recommended reading: Chapter 8; Viruses and Their Replication in “Brock Biology of Microorganisms” Chapter 13; Characterizing and Classifying Viruses, Viroids, and Prions in “Microbiology with Diseases by Taxonomy” 1 Learning objectives ✓ Be able to understand the needs to classify viruses ✓ Be able to understand rationale and approaches for virus classification ✓ Modes and types of virus infection of a cell/host ✓ Molecular mechanisms and sequential stages of viral replication 2  Complexities of Viral Nomenclature No consistent system for naming viruses existed – some are named for the: ✓ The host organism they infect (e.g. African horse sickness virus, swine flu, tobacco mosaic virus) ✓ Geographic locations in which they were first isolated (e.g. Sendai virus [Sendai, Japan] and Coxsackievirus [Coxsackie, New York], Rift Valley Fever virus, Ebola virus, Newcastle Disease virus. ✓ Scientists who first discovered them (e.g. Epstein-Barr virus) ✓ Specific type of disease they cause (e.g. Hepatitis A, B, C, D, E) ✓ Sites in the body from which they were first isolated (e. g. rhinovirus and adenovirus) ✓ Way in which people imagined they were contracted (e.g. dengue, for “evil spirit” and influenza, for the “influence of bad air) ✓ Cytopathology occurring during infection (e.g. Respiratory Syncytial virus) ✓ Combination of all of above (e.g. Rous Sarcoma Virus) The problems with virus nomenclature and classification led to chaos 3 by the 1960s  Taxonomy for Viruses (Classification + Nomenclature) Two main methods for taxonomy of viruses: 1. International Committee on the Taxonomy of Viruses (ICTV) – rebranded in 1971 from International Committee on the Nomenclature of Viruses – 1966. Established by Federation of European Microbiology Societies (FEMS) Virology Division 2. Baltimore System of Virus Classification The system was developed by David Baltimore ICTV and Baltimore classifications David Baltimore are being used together Nobel Prize (1975) 4 ICTV Criteria for Taxonomy of Viruses Primary aim is “to develop, refine and maintain a universal virus taxonomy“ (plant, animal and bacterial viruses) Collection and comparison of characters that distinguish one virus from another o Phenotypic ✓ Molecular composition of the genome ✓ Virion/capsid structure ✓ Presence of an envelop Lowest level ✓ Host range of ICTV ✓ Pathogenicity classification o Genotypic ✓ Sequence similarity ✓ Gene contents ✓ Gene synteny Highest level reflects origins ✓ Gene expression system ✓ Phylogenetic relationships ICTV 2020: 6 realms, 10 kingdoms, 17 phyla, 39 classes, 59 orders, 189 families, 2224 genera, and 9110 species 5 Classification of monkeypox virus: an example o Phenotypic ✓ Natural host ranges (subfamily) ✓ Growth characteristics and host range in cells Morphology of pocks: plague characteristics ✓ Disease characteristics Mortality and morbidity ✓ Serological criteria Plague neutralization tests, cross protection in animals o Genotypic ✓ Amino acid sequence identity Hemagglutinin or A-type inclusion protein ✓ Nucleotide sequence identity Different species