Virology 2 Flashcards
What is poliovirus
A single stranded positive sense RNA virus
What family does poliovirus belong to?
Picornaviridae
Picornaviridae family contains what genus’s?
-Rhinovirus
-Hepatorvirus
-Cardiovirus
-Apthovirus
-Entervirus
Which genus does poliovirus belong to?
Enterovirus
Serotypes of poliovirus:
Type 1 (PV-1)
Type 2 (PV-2)
Type 3 (PV-3)
Structure of poliovirus
-Small (30nm)
-Noneveloped (Naked)
-Icosahedral capsid symmetry
Capsid of poliovirus:
-The capsid is resistant to acidity and detergents
-4 components to the capsid (VP1, VP2, VP3, VP4)
-Capsid has 5 fold axis of symmetry
Poliovirus causes what disease:
-Poliomyelitis
-Disease that leads to distraction of large motor neurons and causes acute flaccid paralysis (AFP)
-Which is transmitted by Faecal-oral
Types of poliomyelitis
- Non paralytic poliomyelitis (causes high fever, back pain, muscle spasms)
- Paralytic poliomyelitis (causes muscle paralysis when relaxed and can become permanent after months)
In what year did polio cases peak in Ireland?
Epidemic lasted from 1948-1964
-Peaked in 1956-1958 (over 500 cases)
When was the last recorded case of polio?
1984
Polio remains endemic in which three countries?
-Pakistan
-Afghanistan
-Nigeria
What does tropism mean?
Tropism is the pattern of host cells which a virus can invade and replicate in
How is Tropism determined:
-By the host cells susceptibility to vital entry
And
-If the cell is permissive for replication
Poliovirus tropism:
-Gut M-cells (enterotropic)
-Large motor neurones (neurotropic)
-Lymphoid cells
Susceptible vs permissive cells:
-All primate cells are susceptible (as they express the PV receptor)
-Only gut and CNS cells are permissive
Genome characteristics of a poliovirus
-Has single copy of genome
-Single open reading frame
-Capsid proteins, protease and Polymerases in between the 5’ and 3’ untranslated regions
Poliovirus replication cycle: steps 1-3
- Virus binds to the receptor (PVR) on susceptible cells and enters the
- Virus uncoats and releases its positive sense RNA
- The RNA is translated into proteins in permissive cell
Poliovirus replication cycle: steps 4-7
- Polymerase makes negative RNA template from positive RNA
- Positive mRNA is made from negative RNA template
- Progeny virus is assembled using the positive mRNA
- Cell Lyses and the virus is release
Polio that replicates in the gut causes what?
A mild fever
Polio that replicates in the CNS caused what?
Poliomyelitis
Viral evasion strategies of polio virus:
-Can survive acidic GI tract
-Replicates quickly
-Infection begins before symptoms appear
Types of polio vaccines
- Oral polio vaccine (OPV)
- Inactivated polio vaccine (IPV)
(Side note) it is recommended that both vaccines are given to a child. One at 2-4 months and the other at 4 years of age
Oral Polio vaccine (OPV)
-Also known as Sabin Vaccine
-As developed by Albert Sabin
-Created in 1963
-Contains a mixture of 3 live, attenuated strains
Inactivated Polio vaccine (IPV)
-Also known as Salk vaccine
-As developed by Jonas Salk
-Created in 1955
-Contains a mixture of 3 formalin inactivated virulent strains
Problem with IPV?
Not all the vaccines were attenuated, meaning that they caused disease.
HIV belongs to what family?
Retroviridae
HIV belongs to what genus?
Lentivirus
Baltimore classification of HIV?
-Group 6
-Reverse transcribing Diploid single stranded RNA viruses
Difference between HIV-1 and HIV-2 strains?
-HIV-1 is more virulent and can be easily transmitted. Causes majority of HIV infections globally
-HIV-2 is less transmítanle and is mostly confined to west Africa
Origin of HIV:
-No single theories is proven
But
-The ‘hunters theory’ is the most accepted.
-In this theory the virus was transferred when a human was bitten by a chimp
Structure of HIV:
-Size (110nm)
-Has two copies of single stranded positive sense RNA
-Icosahedral Capsid symmetry
-Encased by a matrix protein within an envelope
-Envelope is lipid bilateral derived from host membrane but contains viral proteins gp120
Enzymes in HIV:
-Reverse transcriptase
-Integrase
-Protease
Genome organisation of HIV:
-2 copies of genome (9719 nucleotides)
-3 reading frames
-3 major genes (gag, pol, env) inbetween the 5’ and 3’ long terminal repeats (LTR)
-Accessory genes (nef, tat, vif)
The 3 major genes in HIV:
-Gag (capsid, matrix, protease)
-Pol (Reverse transcriptase and integrase)
-Env (envelope proteins such as docking glycoprotein gp120)
HIV tropism:
-M-tropic (Primate cells expressing CD4 and macrophages)
-Lymphotropic
How the immune system works against HIV infection:
- Direct viral killing of infected cells
- Increased rates of apoptosis in infected cells
- Killing of infected CD4+ cells by CD8 Cells
- Death of un infected CD4 ‘bystander cells’ by cell suicide
HIV replication cycle: steps 1-4
- virus binds to receptor on TH cell
- Capsid enters cell and releases positive sense RNA
- +RNA is converted to DNA by reverse transcriptase
- +/- DNA is transported to nucleus and integrates into host genome (provirus)
HIV replication cycle: steps 5-7:
- mRNA made from provirus
- Progeny virus (mRNA) is assembled at cell surface
- immature virus buds from cell then matures
How HIV evaded the immune system:
- Fast replication cycle
- High mutation rate
- Recombinogenic properties of reverse transcriptase
