OIA1010 VIROLOGY

History of Virology

General Characteristic

Much smaller than bacteria:10-400nm; clinical important virus: 18-300nm

Contain DNA/RNA as genomic material

Lacks cellular machinery for self reproduction/ protein synthesis (e.g., endoplasmic reticulum, ribosomes, nucleus, mitochondria, Golgi apparatus) -> cannot generate energy and synthesise protein

Cannot self reproduction: need living cells (host) to replicate - occurs by assembly of individual compartments

Not made up of cells

Small obligated intracellular: nucleic acid surrounded by protective protein coat (capsid)

Shapes of Viruses

Helical Virus

short & stiff or long & bendy

Naked Helical nucleocapsids: rigid & tightly wound into cylindrical shaped (e.g., tobacco virus)

Enveloped Helical nucleocapsids: more flexible & tend to arranged as looser helix (e.g., influenza, measles & rabies)

Polyhedral Virus (equal triangular sides)

Variation in number of capsomeres (e.g., poliovirus: 32; adenovirus 252)

E.g., poilovirus adenovirus, hepatitis B, herpesvirus

Complex Virus (complex caspid, neither Helical nor icosahedral)

May have multiple protein types

Not symmetrical in shape & never enveloped

E.g., bacteriophages & virus

Structure Virus

Viral Genome - genetic material coding for structural proteins & enzyme required for replication was

Contain DNA or RNA but not both

Double stranded or single stranded

Linear or circular

Most DNA virus (double) while most RNA virus (single)

Some RNA virus (e.g., influenza virus & rotavirus) have segmented genome

Viral Proteins - Glycoproteins & Matrix Protein

Surface glycoproteins - viral attachment, membrane fusion for host entry, immunological barrier to resist host immune system, viral antigens

Matrix protein - virus assembly, mediate interaction between viral nucleocaspid proteins and envelope proteins

Viral Envelope

Consists of host-derived lipid bila yer & protein encoded by the virus

Acquired as virus leaves cell via budding

Protect viral RNA or DNA molecules, evade recognition by immune system & facilitate virus entry

Naked Caspid - Protein

Environmentally stable (temperature,acids, proteases, detergent, drying & etc.) -> can survive gut environment

Released from cell lysis

Spread by formites, contact, dust, small droplets (dry out & retain infectivity)

E.g., Adenoviridae, Papillomaviridae, Picornaviridae, Reoviridae

Enveloped Virus - Membrane, Lipid, Protein & Glycoprotein

Environmentally labile (disrupted) -> must remain moist + cannot survive GIT

Modified cell membrane during replication

Released by budding & cell lysis

Spread in large droplets, secretion, organ transplant & blood transfusion

Does not require cell death for spreading

Need antibody & cell-mediated immune response for protection & control

*Shown hypersensitivity & inflammation to cause immunopathogenesis

E.g., Retrovirus, Poxvirus, Flavivirus, Coronavirus

Viral Infection

Viral Multiplication

Grown either in suspension of bacteria of liquid or solid media (plaque method for detection and viral count)

Viral Replication

Lytic Cycle - Death of host cells

Attachement by virion

Entry & Uncoating of Viral DNA

Biosynthesis of nucleic acids

Maturation of virion

Release of virion

Lysogenic Cycle - DNA replication & Viral cells

Attachment - bacteriophages attaches to bacterial cell

Entry - bacteriophages injects DNA into bacterial cell

Integration - Phage DNA recombines with bacterial chromosomes and integrated into chromosomes as prophage

Cell division

Viral Cultivation

To isolate & identify viruses

To prepare viruses for vaccine development

To study viral structures, replication, genetics & effect on host cells

In-vitro Culture

Live animals - lab-bred animals //host specificity

Embryonic bird tissues - viral propagation at bird eggs

Cell or tissues - most widely used but not all viruses grow

Lab Diagnostics

Identification in cell culture

Microscopic identification directly to specimen

Detection of viral antigen/nucleic acids blood or body fluids

Antiviral Vaccine

Active Immunity - Vaccine-killed virus, purified protein subunits, attenuated (weakened virus)

Passive Immunity - Transferred performed antibodies-immunoglobin

Herd Immunity - Vaccine recommended for children aged 0-6 years (e.g., Viral-Hepatitis A & B, influenza, MMR, poliovirus, rota virus, varicella and etc.)

Prions

Infectious proteinaceous particle

Proposed by Stanley Prusiner in 1982

"mad cow disease" & "scapie"