Medical Microbiology Introduction Dr. Sameer Naji, MB, BCh, PhD (UK) Dean Assistant Head of Basic Medical Sciences Dept. Faculty of Medicine The Hashemite University

General Properties of Viruses Viruses are the smallest infectious agents. Most forms of life – animals, plants and bacteria – are susceptible to infection with appropriate viruses.

Properties that distinguish viruses from other microorganisms.: 1. They are obligate intracellular parasites 2. They are inert (nucleoprotein ) filterable Agents 3. Small size: viruses are smaller than other organisms, vary in size (diameter) from 0 nm nm. 4. Genome: either DNA or RNA. The nucleic acid is encased in a protein shell, which may be surrounded by a lipid – containing membrane. The entire infectious unit is termed a virion.

5. Metabolically inert: Viruses have no metabolic activity outside susceptible host cells; they do not possess any ribosomes or protein-synthesizing apparatus, cannot make energy or proteins independent of a host cell, therefore, they multiply only in living cells. On entry, the genome or nucleic acid is transcribed into – or acts as – mRNA which then directs the replication of new virus particles.

Property Viruses Cells Type of nucleic acid DNA or RNA DNA and RNA Proteins Few Many Lipoprotein membrane Enveloped Cell membrane present in present in some viruses all cells Ribosomes Absent Present Mitochondria Absent Present in eukaryotic cells Enzymes None or few Many Multiplication by binary fission No Yes (most cells) Virus vs. Cells

Viruses are Ultramicroscopic

The size of viruses

Terms & Definitions in Virology: Capsid: the protein shell, or coat, that encloses the nucleic acid genome. Capsomeres: morphologic units seen in the electron microscope on the surface of icosahedral virus particles. They represent clusters of polypeptides. Defective virus: a virus particle that is functionally deficient in some aspect of replication.

- Envelope: a lipid-containing membrane that surrounds some virus particles. It is acquired during viral maturation by a budding process through a cellular membrane. - Nucleocapsid: the protein-nucleic acid complex representing the packaged form of the viral genome (capsid + genome ).

- Structural units: the basic protein building blocks of coat. - Subunit: a single folded viral polypeptide chain. - Virion: the complete intact virus particle. Sometimes it is identical with the nucleocapsid (as in papillomaviruses). In more complex virions (as herpesviruses), this includes the nucleocapsid plus a surrounding envelope.

Viral Structure - Overview Schematic overview of the structure of animal viruses ** does not exist in all viruses Nucleic acid Capsid Nucleocapsid Envelope protein Membrane protein Viral envelope** Spike protein

Naming viruses No taxa above Family (no kingdom, phylum, etc) Classified based on structures, size, nucleic acids, host species, target cells. 20 families of animal viruses (7 DNA, 13 RNA) Family name ends in – viridae Subfamily ends in — virinae Genus name ends in – virus Species  Example – Family – Herpesviridae – Subfamily - Herpesvirinae – Genus – Simplex virus – Common name – herpes virus (Herpes simplex virus I (HSV-I) – Disease – fever blisters, cold sores

How are viruses named? Based on: - the disease they cause poliovirus, rabies virus - the type of disease murine leukemia virus - geographic locations Sendai virus, Coxsackie virus - their discovers Epstein-Barr virus - how they were originally thought to be contracted dengue virus (“evil spirit”), influenza virus (the “influence” of bad air) - combinations of the above Rous Sarcoma virus

Structure of Viruses Viruses consist basically of a core of nucleic acid surrounded by a protein coat which is antigenic and specific for each virus type; it protects viral genome from inactivation by adverse environmental as nucleases in blood stream. Structures which make up a virus particle are: Virion, Capsid, Capsomeres, Nucleic acid, and Envelope. It varies in size, shape and symmetry

Virus particles show three types of capsid symmetry: 1. Cubic: in which the particles are icosahedral protein shells with nucleic acid contained inside, has 20 faces, each an equilateral triangle. e.g. adenovirus. 2. Helical: Protein binds around DNA/RNA in a helical fashion (in which the particle is elongated and in the form of a helix or spiral). Most viruses posses an outer envelope. e.g. Coronavirus 3. Complex: in which the particle does not confirm either, e.g. poxvirus.

5 BASIC TYPES OF VIRAL STRUCTURE HELICALENVELOPED HELICAL ENVELOPED ICOSAHEDRAL COMPLEX ICOSAHEDRAL nucleocapsid icosahedral nucleocapsid nucleocapsid helical nucleocapsid lipid bilayer glycoprotein spikes = peplomers

VIRAL STRUCTURE (virion) 1.Protect genome during passage from one cell to another 2.Aid in entry process 3.Package enzymes for early steps of infection

1. Helical capsid Rod-shaped capsomers Coil around hollow center Nucleic acid is kept inside – wound-up within tube (Helix ) Morphological types CAPSID STRUCTURE

Helical – capsid surrounds RNA like hollow tube Ex: Influenza, measles, rabies (enveloped) Morphological types

Helical symmetry

2. icosahedral 20-sided with 12 corners Vary in the number of capsomers Each capsomer may be made of 1 or several proteins Some are enveloped Morphological types PROTOM ER

Cubic or icosahedral symmetry

ICOSAHEDRAL SYMMETRY

Adenovirus

Enveloped helical virusEnveloped icosahedral virus

Helical California Encephalitis Virus Coronavirus Hantavirus Influenza Virus (Flu Virus) Measles Virus ( Rubeola) Mumps Virus Para influenza Virus Rabies Virus Respiratory Syncytial Virus(RSV)

Icosahedral Adeno-associated Virus (AAV) Adenovirus B19 Coxsackievirus - A Coxsackievirus - B Cytomegalovirus (CMV) Eastern Equine Encephalitis Virus (EEEV) Echovirus Epstein-Barr Virus (EBV) Hepatitis A Virus (HAV) Hepatitis B Virus (HBV) Hepatitis C Virus (HCV) Hepatitis Delta Virus (HDV) Hepatitis E Virus (HEV) Herpes Simplex Virus 1 (HHV1) Herpes Simplex Virus 2 (HHV2) Human Immunodeficiency Virus (HIV) Human T-lymphotrophic Virus (HTLV) Norwalk Virus Papilloma Virus (HPV) Polio virus Rhinovirus Rubella Virus Saint Louis Encephalitis Virus Varicella-Zoster Virus (HHV3) Western Equine Encephalitis Virus (WEEV) Yellow Fever Virus

Complex viruses Have additional or special structures Examples: Poxviruses – lack normal capsid – instead, layers of lipoprotiens and fibrils on surface cross sectionsurface view

A bacteriophage A bacteriophage is any one of a number of viruses that infect bacteria. They do this by injecting genetic material, which they carry enclosed in an outer protein capsid. The genetic material can be ssRNA, dsRNA, ssDNA, or dsDNA ('ss- ' or 'ds-' prefix denotes single-strand or double-strand) along with either circular or linear arrangement.

Phage - viruses have a polyhedral head, helical tail and fibers for attachment.