history, replication

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virus latin word

means liquid poison

first reported a virus that caused mosaic disease in tobacco plant

1892: Dimitri Ivanofsky

1892: Dimitri Ivanofsky

first reported a virus that caused mosaic disease in tobacco plant

repeated Ivanofsky’s work and concluded the “invisible fluid”

1898: Dutch botanist Martinus Beijerinck

1898: Dutch botanist Martinus Beijerinck

repeated Ivanofsky’s work and concluded the “invisible fluid”

reported FMD for the first time

1897: Loeffler and Frosch

1897: Loeffler and Frosch

reported FMD for the first time

invented electron microscopy

1932: Max Knoll and Ernst Ruska

1932: Max Knoll and Ernst Ruska

invented electron microscopy

propagated virus in embryonating eggs

1931: Goodpasture and Woodruff

1931: Goodpasture and Woodruff

propagated virus in embryonating eggs

developed the cell culture technique that greatly facilitated the study of viruses

1949: John Franklin Enders

1949: John Franklin Enders

developed the cell culture technique that greatly facilitated the study of viruses

Acquired immonodeficiency syndrome (AIDS) virus and family

HIV-1; Retrovirus

cervical carcinoma virus and family

Human papillomavirus types 16, 18, 31; Papillomavirus

chickenpox virus and family

Varicella virus; Herpesvirus

"""cold sores"" virus and family"

Herpes simplex virus type 1; Herpesvirus

common cold virus and family

Adenoviruses; AdenovirusCoronaviruses; CoronavirusRhinoviruses; Picornavirus

diarrhea virus and family

Norwalk virus; CalicivirusRotavirus; Reovirus

Genital herpes virus and family

Herpes simplex virus type 2; Herpesvirus

hemorrhagic fevers virus and family

• Dengue virus; Flavivirus

• Ebola and Marburg viruses; Filovirus

• Lassa fever virus; Arenavirus

Hepatitis virus and family

Hepatitis A virus; PicornavirusHepatitis B virus; HepadnavirusHepatitis C virus; Flavivirus

Influenza virus and family

Influenza A and B virus; Othomyxovirus

Measles virus and family

Measles virus; Paramyxovirus

Mononucleosis virus and family

Epstein-Barr virus;Herpesvirus

Cytomegalovirus; Herpesvirus

Mumps virus and family

Mumps virus; Paramyxovirus

Poliomyelitis virus and family

Poliovirus types 1,2, and 3; Picornavirus

Rabies encephalitis virus and family

Rabies virus; Rhabdovirus

SARS virus and family

SARS coronavirus; Coronavirus

smallpox virus and family

Variola virus; Poxvirus

warts virus and family

Human papillomavirus; Papillomavirus

yellow fever virus and family

yellow fever virus; Flavivirus

Virus particles contain

A nucleic acid genome (either DNA or RNA) A protein coat (capsid) that encloses the genome In some cases, a lipid membrane (envelope)

The infectious virus particle is called a

virion

Virus particles are very small: … in diameter.

between 20 and 500 nanometers (nm)

viral RNA types

• Positive sense (5′ to 3′)

• Negative sense (3′to 5′)

• single-strand

• whole-genome viruses (Paramyxoviridae)

• segmented genome viruses (Orthomyxoviridae— six, seven, or eight segments; Bunyaviridae— three segments; Arenaviridae—two segments)

example of single stranded DNA virus

circular super-coiled genome of the Polyomaviridae and Papillomaviridae (5-8 kbp) linear Herpesviridae (125-235 kbp)

example of double stranded DNA virus

linear (Parvoviridae) or circular (Circoviridae and Anelloviridae)

outer capsid proteins function

mediate the attachment of the virus specific receptors on the host cell surfaceprotect the genetic material

the major determinant of the species and organ specificity of the virus

outer capsid proteins

mediate the attachment of the virus specific receptors on the host cell surface

outer capsid proteins

protect the genetic material

outer capsid proteins

important antigens that induce neutralising antibody and activate cytotoxic T cells to kill virus-infected cells

outer capsid proteins

Structural proteins functions

to protect the genomic nucleic acid and associated enzymes from inactivation; to provide receptor- binding sites for initiation of infection; to initiate or facilitate the penetration of the viral genome into the correct compartment of the cell for replication

protect the genomic nucleic acid and associated enzymes from inactivation

Structural proteins (internal viral proteins)

provide receptor- binding sites for initiation of infection

Structural proteins (internal viral proteins)

initiate or facilitate the penetration of the viral genome into the correct compartment of the cell for replication

Structural proteins (internal viral proteins)

what is Viral envelope composed of

Lipoprotein membrane composed of lipid derived from host cell membrane

acquired as the virus exits from the host cell in the process called budding

Viral envelope

virus with envelope budding sites

plasma membrane, nuclear membrane, Golgi, or the endoplasmic reticulum

Helical symmetry is defined by two parameters:

u, the number of subunits per turn, p, the displacement along the helix axis between one subunit and the next. P, the pitch of the helix, is the distance along the helix axis that corresponds to exactly one turn of the helix;

the number of subunits per turn

u

the displacement along the helix axis between one subunit and the next

p

the pitch of the helix, is the distance along the helix axis that corresponds to exactly one turn of the helix

P

Viruses are classified into related groups based on: 7

• Genome composition (DNA or RNA, single- or double stranded)

• Genome topology (linear or circular; single or multiple segments)

• Capsid symmetry

• Presence or absence of an envelope

• Genetic relatedness (nucleotide and amino acid sequence similarity)

• Mechanisms for expressing messenger RNAs and replication of genomes

• Host organisms

Viruses are classified into species, genera, families, and (in some cases) orders, within the following categories: 7

Viruses with single-stranded DNA genomes Viruses with double-stranded DNA genomes Viruses with positive-strand RNA genomes Viruses with negative-strand RNA genomes Viruses with double-stranded RNA genomes Viruses that use a reverse transcriptase Satellite viruses, satellite nucleic acids, and viroids

how were virus initially classified

viruses initially were classified according to the diseases they caused, shared physical and chemical properties, and serologic cross-reactivity

genetic comparisons of different viruses to facilitate taxonomic classifications

Nucleic Acid sequencing

phylogenetic comparisons to determine the evolutionary development and history of viral species.

Nucleic Acid sequencing

establish, refine, and maintain a universal system of virus taxonomy

The International Committee on Taxonomy of Viruses (ICTV) (1966)

in 2011 how many virus species, generam subfamilies, families and orders are there

2284 species of virus and viroid distributed amongst 349 genera, 19 subfamilies, 87 families, and 6 orders.

members have several properties in common but all do not have to share a single defining property

polythetic class

polythetic class

members have several properties in common but all do not have to share a single defining property

a system used to classify viruses based on their manner of messenger RNA (mRNA) synthesis

Baltimore Classification

Baltimore Classification

a system used to classify viruses based on their manner of messenger RNA (mRNA) synthesis

used to culture viruses

live animals- SPF: specific pathogen free embryonated chicken eggs Cell culture systems

became a standard culturing system for routine isolation and propagation of avian viruses and select mammalian viruses

embryonated chicken eggs

any observable cellular characteristic that is present in virus- infected cells and which is absent in uninfected cells maintained under identical growth conditions

Cytopathic effect (CPE)

Cytopathic effect (CPE) morphological changes

rounding, clumping, shrinkage, and detachment of individual cells from the cell culture matrix

mediates Hemadsorption

mediated by viral glycoproteins that are expressed on the cell surface and which bind to receptors on the red blood cells.

where does Hemadsorption occur

occurs with viruses that bud from the plasma membrane, and may be specific for red blood cells of a given animal species

show the ability to hemagglutinate red blood cells in cell-free medium

Hemadsorption

number of infectious virus particles added per susceptible cell

multiplicity of infection (m.o.i.)

are intracellular abnormalities, commonly new structures, which arise as a direct consequence of virus infection.

Inclusion bodies

immunologically based assays

fluorescent antibody assay (immunofluorescence assay, IFA)immunohistochemical staining assay

Steps in virus replication cycle

binding to cell receptorentry and uncoatingearly gene expressionreplication of viral genomelate gene expressionassembly of virionsexit

Attachment

Virions bind to receptors on the cell surface Virus-coded proteins on the surface of the virion bind to specific proteins, carbohydrates, or lipids on the cell surface

Human immunodeficiency virus Family and receptor

Retroviridae CCR5, CCR3, CXCR4 (heparan sulfate proteoglycan)

Avian leukosis/sarcoma virus Family and receptor

Retroviridae Tissue necrosis factor-related protein TVB

Murine leukemia virus E Family and receptor

Retroviridae MCAT-1

Bovine leukemia virus Family and receptor

Retroviridae BLV receptor 1

Poliovirus Family and receptor

Picornaviridae PVR (CD155)—Ig family

Coxsackievirus B Family and receptor

Picornaviridae CAR (coxsackie and adenovirus receptor)—Ig family

Human rhinovirus 14 Family and receptor

Picornaviridae ICAM-1 (intercellular cell adhesion molecule-1)—Ig family

Echovirus 1 Family and receptor

Picornaviridae a2B1 integrin VLA-2

Foot-and-mouth disease virus— wild-type virus Family and receptor

Picornaviridae Various integrins

Foot-and-mouth disease virus— cell-culture-adapted Family and receptor

Picornaviridae Heparan sulfate proteoglycan

Feline calicivirus Family and receptor

Caliciviridae fJAM-A (feline junction adhesion molecule-A)

Adenovirus 2 Family and receptor

Adenoviridae CAR-Ig family

Adenoviruses Family and receptor

Adenoviridae avB3, avB5 integrins

Herpes simplex virus 1 Family and receptor

Herpesviridae HveA (herpes virus entry mediator A), heparan sulfate proteoglycan, others

Human cytomegalovirus Family and receptor

Herpesviridae Heparan sulfate proteoglycan

Epstein–Barr virus Family and receptor

Herpesviridae CD21, complement receptor 2 (CR2)

Pseudorabies virus Family and receptor

Herpesviridae CD155—Ig family

Feline parvovirus Family and receptor

Parvoviridae TfR-1 (transferrin receptor-1)

Adenovirus-associated virus 5 Family and receptor

Parvoviridae a(2,3)-linked sialic acid

Influenza A virus Family and receptor

Orthomyxoviridae Sialic acid

Influenza C virus Family and receptor

Orthomyxoviridae 9-O-acetylsialic acid