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BI302 > S.M Lecture 2 > Flashcards

S.M Lecture 2 Flashcards

1
Q

Classification of Polioviruses

A
  • Family - Picornaviridae (150 varites)
  • Genus - 5 Genera, Rhinovuris, Hepatovirus, Cardiovirus, Apthovirus, Enteroviru (includes poliviruses)
  • Species (Polio Virus)

Look at slide 7 for more on genus

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2
Q

Characteristics of Polioviruses

A
  • Small (30nm).
  • 3 serotypes (Type I, II, or III)
  • Single strand “+ sense” RNA
  • Nonenveloped (Naked)
  • Icosahedral Capsid symmetry
  • Capsid is resistant to acidity, & detergents
  • 4 components to capsid: VP1 (blue), VP2 (red), VP3 (yellow), VP4 (internal) proteins
  • Xray crystallography reveals a canyon about 5-fold axis of symmetry
  • Causes - paralytic poliomyelitis
  • Transmission: Faecaloral
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3
Q

Paralytic poliomyeltitis

A
  • Depicted in Egyptian wall painting
  • Most polio infections are unapparent/mild 1-2% reach CNS…high fever, back pain, muscle spasms (non paralytic poliomyelitis)
  • In 0.1% of cases…partial/complete muscle paralysis when relaxed (paralytic poliomyelitis)
  • If paralysis remains after months becomes permanent
  • Destruction of large motor neurones causes acute flaccid paralysis (AFP)
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4
Q

Cure for Polio - salk vaccine

A
  • 1955 - injectable salk vaccine.
  • Salk vaccine - formalin inacticated at neutral pH.
  • Probelm as not all vaccine as attenuated

Attenuated microorganisms can be used in vaccines, where they stimulate an immune response without causing disease, and can provide long-lasting protection against future infections by the same microorganism.

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5
Q

Cure for Polio - Sabin

A
  • 1963 Sabin Vaccine
  • Also known as the oral polio vaccine (OPV)
  • The vaccine is made from 3 weakened, live polio virus strains, which are given orally in a sugar cube or liquid drops.
  • The strains are attenuated meaning that they replicate but do not cause disease
  • Developed by Albert Sabin
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6
Q

Innactivated Polio Vaccine

A
  • IPV contains polioviruses of three types which have been inactivated by formaldehyde. It is only available as a combination vaccine
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7
Q

Tropism

A

The pattern of host cells which a virus can invade and replicate in (i.e. the biological niche)

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8
Q

How is tropisim determined?

A

Tropism is determined by the host cells’ to viral entry (often expression of a receptor), and whether the cell is susceptibility permissive for replication (intracellular biochemistry)

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9
Q

Poliovirus tropism

A

Gut M neurones, ( neurotropiccells ( enterotropic ), lymphoid cells.

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10
Q

Do all primate cells express the PV receptor?

A
  • All primate cells express the PV receptor (PVR; CD155) (susceptible), but only gut, CNS and certain other cells are permissive
  • Polio virus binds to receptor (PVR) on susceptible cells
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11
Q

Poliovirus: Genome organisation

A
  • single copy of genome (+ve sense)
  • single open reading frame (very simple)
  • untranslated regions (UTR), capsid proteins, proteases, polymerase/RNA synthesis
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12
Q

Poliovirus replication cycle

A
  1. Virus binds to receptor (PVR) on susceptible cell & enters
  2. Virus uncoats to release +RNA (Red)
  3. +RNA translated to proteins (including polymerase) in permissive cell
  4. Polymerase makes -RNA template from the +RNA
  5. Now, +RNA made from -RNA template
  6. Progeny virus assembled (using mRNA from 5 as its nucleic acid)
  7. Cell Lyses and virus released
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13
Q

Viremia

A

Virus in blood

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14
Q

Classification of HIV virus

A

Family - retroviridae
Genus - Lentiviruses
Includes: Includes: HIV-1, HIV-2, SIV, FIV, BIV, Visna-Maedi virus
Species - HIV

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15
Q

Which species of HIV infect humans?

A

HIV-1 and HIV-2

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16
Q

HIV-1

A
  • HIV-1 is thought to have originated in sourthern cameroon after jumping from wild chimps to humans during 20th century
  • HIV-1 is more virulent. Easily transmitted and is the cause of the majority of HIV infections globally.
17
Q

HIV-2

A
  • HIV2 may have originated from an Old World monkey of Guinea- Bissau, Gabon and Cameroon called the Sooty Mangabey
  • HIV-2 is less transmittable and is largely confined to West Africa
18
Q

Hunter Theory

A
  • A variety of theories exist explaining the transfer of HIV to humans, No single hypothesis is unanimously accepted
  • The most widely accepted theory is so called ‘Hunter’ Theory….. transference of the virus from chimp to human when a human was bitten by a chimp or was cut while butchering one, and the human became infected
  • Mutation of SIV
19
Q

Main sympthoms of AIDS

A
  • Central: Encephalitis, Meningitis
  • Eyes - Retinitis
  • Lungs: - pneumocytis pneumonia, tuberclosis (multiple organs)
  • Skin - Tumors
  • Gastrointestinal: -Esophagitis, Chronic diarrhea,Tumors.
20
Q

Human Immunodeficiency Virus (HIV)

A
  • Size = 110nm
  • 2 copies of Single strand “ + sense” RNA
  • Reverse transcriptase, integrase, protease
  • Icosahedral Capsid symmetry
  • Encased by a matrix protein within an envelope
  • Envelope is lipid bilayer derived from host membrane but contains viral protein gp120
  • Causes Acquired Immunodeficiency disease (AIDS)
21
Q

What way is HIV transmitted?

A
  • Sexually transmitted (STD) or other exchange body fluids (i.v. drug abuse, vertical, unscreened blood donation)
22
Q

HIV: Genome organisation

A
  • 2 copies of genome (9719 nucleotides)
  • Genes encoded in all 3 reading frames
  • alternative splicing
  • Long terminal Repeats (LTR)
  • 3 major genes: gag (capsid, matrix & protease), pol (RT & integrase), env (envelope proteins gp120)
  • Accessory genes: nef, tat, vif (regulatory)
23
Q

HIV Tropsim

A
  • primate cells expressing CD4 (such as helper CD4+ T cells) and macrophages (M-tropic)
  • Also, either/or the chemokine receptor CCR5 (macs R5 HIV) or CXCR4 (T-cells X4 HIV)
  • Lymphotropic
  • HIV infection
24
Q

What does it mean that HIV is lymphotropic?

A
  • HIV (Human Immunodeficiency Virus) is lymphotropic, which means it has a particular affinity for targeting the lymphatic system.
  • HIV primarily targets and infects CD4+ T cells, which are a type of white blood cell that plays a critical role in the body’s immune system
25
Q

What are the four mechanisms for HIV?

A
  1. direct viral killing of infected cells
  2. increased rates of apoptosis in infected cells
  3. killing of infected CD4+ T cells by CD8 cytotoxic lymphocytes that recognize infected cells.
  4. Death of uninfected CD4 ‘bystander cells’ cells by cell suicide
26
Q

HIV Replication cycle

A
  1. Virus binds to receptor (CD4, CCR5, CXCR4, on helper T cell)
  2. Viral core (capsid) enters cell & releases +RNA
  3. +RNA is converted to DNA by RT
  4. +/- DNA is transported to nucleus and integrated into host genome (Provirus)
  5. mRNA for viral proteins & viral genomes made from provirus +/- DNA template
  6. Progeny virus assembled at cell surface
  7. Immature virus buds from cell then matures
27
Q

Reasons for genetic variability…evasion of host immune system

A
  1. Very fast replication cycle, with the generation of 10 every day,
  2. High mutation rate of approximately 3 x 10-5 per nucleotide base per cycle of replication
  3. Recombinogenic properties of reverse transcriptase

Thus…many variants of HIV are present in a single infected patient in the course of one day.

BI302 (11 decks)

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