SM L2 Flashcards
(27 cards)
Classification of Polioviruses
Family - Picornaviridae (150 varites)
Genus - 5 Genera, Rhinovuris, Hepatovirus, Cardiovirus, Apthovirus, Enteroviru (includes poliviruses)
Species (Polio Virus)
Characteristics of Polioviruses
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
Paralytic poliomyeltitis
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)
Cure for Polio - salk vaccine
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
Cure for Polio - Sabin
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
Innactivated Polio Vaccine
PV contains polioviruses of three types which have been inactivated by formaldehyde. It is only available as a combination vaccine
Tropism
The pattern of host cells which a virus can invade and replicate in (i.e. the biological niche)
How is tropisim determined?
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)
Poliovirus tropism
Gut M neurones, ( neurotropiccells ( enterotropic ), lymphoid cells.
Do all primate cells express the PV receptor?
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
Poliovirus: Genome organisation
single copy of genome (+ve sense)
single open reading frame (very simple)
untranslated regions (UTR), capsid proteins, proteases, polymerase/RNA synthesis
Poliovirus replication cycle
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
Viremia
Virus in blood
Classification of HIV virus
Family - retroviridae
Genus - Lentiviruses
Includes: Includes: HIV-1, HIV-2, SIV, FIV, BIV, Visna-Maedi virus
Species - HIV
Which species of HIV infect humans?
HIV-1 and HIV-2
HIV-1
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.
HIV-2
*HIV-2 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.
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.
Main symptomes of AIDS
Many people with HIV
have no symptoms for
several years. Others
may develop symptoms
similar to flu, usually two
to six weeks after
infection.
Human immunodeficiency virus
- 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) - Transmission: Sexually transmitted
(STD) or other exchange body fluids
(i.v. drug abuse, vertical, unscreened
blood donation) - 2 strains (HIV I, II).
What way is HIV transmitted
sexually or body fluids
HIV; Genome organisation
- 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)
HIV tropism
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).
What does it mean that HIV is lymphotropic?
HIV infection…….you see LOW levels of CD4+ cells
