Viruses

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VIRULOGY - INTRODUCTION

Dr. Ashish V. Jawarkar, M.D. (Path)

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History

Louis Pasteur was the first to suspect that organisms smaller than bacteria existed

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Viral diseases

Common cold Rabies AIDS Influenzae SARS

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Morphology

Size – Ultramicroscopic Seen only by electron microscope

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Size of viruses

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The Viral Structures and Shape

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Central nucleic acid (DNA or RNA) Capsid May / may not have outer covering

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Capsids All viruses have capsids- protein coats

that enclose & protect their nucleic acid

Each capsid is constructed from identical subunits called capsomers made of protein

2 types: helical iscosahedral

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Shape of Viruses, determined by the arrangement of proteins (capsomers) in the capsid

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Helical

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Icosahedral

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Additional Structures in some Viruses, envelope and surface proteins

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Function of the envelope

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Naming viruses

No taxa above Family (no kingdom, phylum, etc)

19 families of animal viruses Family name ends in -viridae ,

Herpesviridae Genus name ends in -virus,

Simplexvirus Herpes simplex virus I (HSV-I)

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Family – Herpesviridae Genus – Varicellovirus Common name – chickenpox

virus Disease - chickenpox

EXAMPLE of VIRAL TAXONOMY

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VIRAL REPLICATION

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Phage Replication

6 steps in phage replication

1. adsorption – binding of virus to specific molecule on host cell

2. penetration –genome enters host cell3. replication – viral components produced4. assembly - viral components assembled5. maturation – completion of viral

formation6. release – viruses leave cell to infect

other cells

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Penetration

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Bacteriophage assembly line

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Not all bacteriophages lyse cells Temperate phages insert their viral DNA

into the host chromosome & viral replication stops at there until some later time.

Lysogeny- bacterial chromosome carries phage DNA

Impact of Bacteriophages

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Types of viruses

DNA and RNA viruses replicate in different manner.

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The Most Common DNA Viruses

Adenoviruses Cytomegalovirus Epstein-Barr virus Hepatitis B virus Herpes simplex Types 1 &2 Papovavirus Varicella-Zoster virus

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The RNA Viruses Dengue viruses Ebola virus Picorna viruses Hanta virus Hepatitis A and C HIV Influenza virus Mumps virus Norwalk virus Corona virus Rotavirus Rubeola Virus RSV

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VIRAL CPE

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Cytopathic effects- virus-induced damage to cells

1. changes in size & shape2. cytoplasmic inclusion bodies3. nuclear inclusion bodies4. cells fuse to form multinucleated

cells5. cell lysis6. alter DNA7. transform cells into cancerous cells

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Cytopathic changes in cells

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Inclusion body

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Transformation or conversion of cell division to cells that divide indefinitely ( tumors ,warts)

Induces hyperplasia of the host cells

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Host Response to Viral Infections

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Host Cell response includes :

Antibody response

Cellular Immune response

Interferon production

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Antibody Response

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Cellular Immune response

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Interferons

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Diagnostic Virology

How do we grow viruses?

Obligate intracellular parasites require appropriate

cells to replicate.

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Growing animal viruses

1. live animals 2. bird embryos – chicken, duck;

intact, self-supporting unit, sterile, self-nourished

3. cell culture- cell lines

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Virus laboratory

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Cell Culture

Cell culture is the process by which prokaryotic, eukaryotic or plant cell are grown under controlled conditions.

"cell culture" now , refers to the culturing of cells derived from multicellular eukaryotes, especially animal cells.

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Cell lines

Cells that are cultured directly from a subject are known as primary cells.

primary cell cultures have limited lifespan after a certain number of population doublings cells

undergo the process of senescence and stop dividing, while generally retaining viability.

An established or immortalised cell line has acquired

the ability to proliferate indefinitely either through random mutation or deliberate modification, such as artificial expression of the telomerase gene

There are numerous well established cell lines representative of particular cell types.

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Established human cell lines

One of the earliest human cell lines, descended from Henrietta Lacks, who died of cervical cancer .

The cultured HeLa cells shown below have been stained with Hoechst turning their nuclei blue.

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Tissue Culture

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Tissue Culture

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No virus virus

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Egg Inoculation

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Egg inoculation …

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Diagnosis of viral diseases More difficult than other agents Consider overall clinical picture Take appropriate sample

Infect cell culture- look for characteristic cytopathic effects

Screen for parts of the virus Screen for immune response to virus

(antibodies)

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diagnosis

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Thank you end of lecture !