Viruses and Prions Flashcards
What type of nucleic acid do viruses have?
Either DNA or RNA (unlike bacteria which have both)
What does the term ‘metabolically inert’ mean?
- Viruses cannot reproduce on their own
- Need to hijack components of host in order to reproduce
- They do not possess ribosomes/cannot perform protein synthesis
What is a bacteriophage?
A virus that infects bacteria
What size is a virus? (in nm)
1000-3000 nm
What is the virus protected by?
- Envelope - lipid membrane (around some viruses)
- Capsid: protein shell
What are capsids composed of?
Capsomeres (protein units)
What are some of the modes of viral transmission?
- Inhalation via respiratory tract
- Ingestion via G.I. tract
- Inoculation: skin abrasions mucous membranes, transfusions, transplants, injections, bites
- Congenital: mother to foetus
- Sexual transmission
Which organ system does rabies affect?
Nervous system
Which organ system does influenza affect?
Respiratory system
Which organ does herpes simplex affect?
Localised disease of the skin and and mucous membranes
Which organ does adenovirus affect?
Eye
Which organ does hepatitis affect?
Liver
Which organs do mumps affect?
Salivary glands
Which organ system does norovirus affect?
G.I. tract
How is HIV commonly transmitted?
Sexually transmitted
What does ‘cytopathic effect’ refer to in viral infections?
- Structural changes in host cells that are caused by viral invasion
- Can result in cell death
What does ‘transformation’ refer to?
Cell not killed, changed to cancerous cell
What does ‘latent infection’ mean?
Virus remains in cell, no obvious effect on cell function
What are the stages in viral replication?
- Attachment
- Penetration
- Uncoating
- Synthesis of viral components
- Assembly
- Release
How many people died from the flu in 1918?
40 million
What are the 3 different types of influenza virus (RNA viruses)?
Type A
Type B
Type C
What are the 2 key molecules on the surface of viruses that are often targeted by vaccines?
Haemagglutinin
Neuroaminidase
What type of nucleic acid do influenza viruses contain?
RNA
What is haemagglutinin?
- Glycoprotein
- Sialic acid binding
- 14 H types
How many types of haemagglutinin are there?
14
What is neuraminidase?
- Glycoprotein
- Virion release
- 9 N types
How many types of neuraminidase are there?
9
Which molecule present on the surface of the influenza virus enables virion release?
Neuraminidase
Which molecule present on the surface of the influenza virus binds to silica acid?
Haemagglutinin
What is antigenic drift?
- Minor change
- Point mutations
- Results in epidemics
- A, B and C drift
- Haemagglutinin and neuraminidase change shape -> allow virus to change shape
Why is antigenic drift less dangerous to the host compared to antigenic shift?
Fragments of the outside of the virus can still be recognised by the immune system in antigenic drift (only small changes); whereas in antigen shift, there is a dramatic change in the outside structure of the virus. Virus can evade immune system
What is antigenic shift?
- Results in a major change the the outside structure of the virus
- Involves recombination
- Results in pandemics
- Only Type A are capable of antigenic shift
Which type(s) of influenza virus are capable fo antigenic shift?
Type A only
Which type(s) of influenza virus are capable fo antigenic shift?
Type A
What type of specimens can be used to make a virological diagnosis?
Swabs, faeces, aspirates, plasma, CSF, vesicle fluids, urine
What is PCR (polymerase chain reaction) used for?
To amplify target pieces of DNA for analysis
Name 2 methods of serology
ELISA
Western Blotting
Which antibody is released in the primary response?
IgM
Which antibody is released in the adaptive response?
IgG
What does BSE stand for?
Bovine Spongiform Encephalopathy
What are the ‘links’ in the chain of infection?
- Infectious agent
- Reservoir
- The portal of exit
- The mode of transmission
- The portal of entry
- The susceptible host
What is a prion protein?
An infectious agent devoid of nucleic acid
What are the 3 classes of prion disease?
- Infectious
- Genetic
- Sporadic
How do prion proteins cause disease?
- Accumulation of abnormal form of a natural protein
- Conformational changes associated with specific diseases
What is Creutzfeld-Jacob Disease (CjD)?
- Brain disease
- Caused by accumulation of abnormal protein (prion) aggregates in the brain
- No cure
Which structural abnormality is common in infectious prions?
Structure tends to contain lots of beta pleated sheets (normal prion forms contain more alpha chains)
Which unusual property of prions make them difficult to kill?
Resistant to thermal inactivation
What was BSE in human populations linked to?
Consumption of contaminated bovine products
What does ‘iatrogenic transmission’ refer to?
Spread of a pathogen through a medical procedure of treatment e.g. contaminated instruments, not sterilising instruments between patients
