25-27 - Virology (Virus structure, transmission and replication)) Flashcards
Viruses are obligate…
Intracellular parasites
A purified virus particle is known as a…
Virion
Virions can be seen using…
Electron microscopy
Outline the basic structure of a virus…
- Genome (DNA/RNA DS/SS) within nucleocapsid
- Protein capsid comprised of subunits (capsomeres)
- An envelope (host cell phospholipid membrane)
- Surface or envelope proteins
Give 3 approaches to the classification of viruses…
- Morphology
- Biology (tissue type)
- Genome organisation & replication (Baltimore classification)
The Baltimore classification (Classes 1-7) groups viruses based on their routes to the production of mRNA.
Broadly, DNA viral genomes can be transcribed by host polymerases, however RNA viruses…
Must encode their own RNA dependent polymerases (although some RNA viruses (retroviruses) use reverse transcriptase to generate DNA)
What is a sub-virus? Give 4 examples…
Sub-viruses are virus like entities that fail to meet some of the minimum criteria for a true virus.
Examples include:
- Satellite viruses (requires helper virus)
- Virusoids (genome lacks code for structural proteins, requires helper virus)
- Viroid (naked infectious RNA)
- Prions (infectious proteins- BSE, CJD)
Outline the cycle of infection…
- transmission
- entry
- primary site replication
- spreading within host
- shedding
Outline 5 routes of horizontal transmission…
- Respiratory
- Fecal/oral (gastrointestinal)
- Sexual
- Urinary
- Mechanical (needles, piercing, surgery etc)
Give 3 examples of viruses transmitted via the fecal/oral route…
- Rotaviruses (vomiting, diarrhea, fever)
- Hepatitis A (liver inflammation, jaundice)
- Poliovirus (1% of cases cause irreversible muscle paralysis)
Give 4 examples of viruses transmitted sexually…
- HIV
- Hepatitis B (HBV) (may become chronic and lead to liver cancer)
- Human Papilloma Virus (HPV) (Types 16 & 18 - cervical and penile cancer)
- Herpes Simplex Virus (HSV) (genital blisters, latent infection)
Urinary transmission is very rare. Give the reason why and 2 examples of viruses which can nonetheless be transmitted this way…
Rare due to glomerular filtration
Examples: Cytomegalovirus, poliovirus
Mechanical transmission is typical for which type of viruses?
Blood-borne
Vertical transmission is transmission from…
(and how might this occur?)
Mother to child
This may be transplacental (as in Rubella)
During birth (as in Herpes)
After birth (via breastmilk or saliva)
Transmission of viruses from animal to man is known as…
Zoonosis
The animal that acts as a reservoir for a zoonotic virus is known as the…
Primary host
The animal that transmits a zoonotic virus is known as the…
Vector
Give two examples of zoonosis, stating the primary host and the vector…
-
Rabies virus
- Fox is both primary host and vector
-
Yellow fever virus
- Primates act as primary host
- (Female) mosquitos act as vector
Preventing transmission is crucial to controlling viral infections.
List 7 environmental and social factors that influence viral transmission…
- Sanitation (poor sanitation -> fecal/oral transmission)
- Climate (viral vectors, human behaviours etc)
- Viral vectors (such as mosquitos-> zoonotic transmission)
- Poverty (higher likelihood of poor health, lack of access to healthcare etc)
- Behaviours (intravenous drug use -> mechanical transmission)
- Population density (faster spread)
- Healthcare (availability and quality)
Outline the 6 stages of viral multiplication…
- Attachment
- Penetration
- Uncoating
- Biosynthesis
- Assembly
- Release
6 Stages of Viral Multiplication
1. Attachment
Attachment occurs when viral surface proteins gain access to host cells via cell surface proteins, which in this case are known as…
Virus receptors
The virus receptors on the host cell are problematic as drug targets because…
They serve an important functions for host cells
6 Stages of Viral Multiplication
2. Internalisation
State and distinguish between the two means of viral internalisation…
a) Fusion From Without - entry by fusion of viral envelope w/ plasma membrane
b) Receptor Mediated Endocytosis - entry by endocytosis (after which virus escapes the endosome, by envelope fusing with endosome, or via pore if non-enveloped)
6 Stages of Viral Multiplication
3. Biosynthesis
Biosynthesis can be divided into 3 processes…
- Replication of the genome
- Packaging of genome
- Altering metabolism of host cell
6 Stages of Viral Multiplication
3. Biosynthesis
Viruses must compete for host cell ________ .
Many viruses have evolved mechanisms to outcompete ____ ____, such as _____ - which allows translation of viral mRNA without ____________ .
6 Stages of Viral Multiplication
3. Biosynthesis
Viruses must compete for host cell ribosomes.
Many viruses have evolved mechanisms to outcompete host mRNA, such as IRES - which allows translation of viral mRNA without the presence of a 5’ cap.
Virally infected cells often inhibit protein synthesis. This can be due to either the virus itself or…
Interferon released in response to the virus
Viral proteins are also subject to post-translational modifications (such as glycosylation, acylation and lipoylation).
Some viruses encode a polyprotein.
Give an example of a virus that encodes a polyprotein and state how this is modified post-translationally.
Hepatitis C encodes a polyprotein.
Post-translational modification breaks up the polyprotein
Name the 5 structural forms of virus…
- Naked icosohedral
- Naked helical
- Enveloped icosohedral
- Enveloped helical
- Complex
6 Stages of Viral Multiplication
5. Release
State the 3 ways viruses may be released from the host cell…
- Budding
- Cell Lysis
- Cell to Cell (pores or membrane fusion)
Enveloped viruses aquire their membranes from…
Host cell lipid bilayers (usually plasma membrane when budding)
What condition present in the endosome may trigger envelope fusion with or breach of the virus-containing endosome?
Low pH
