Viral properties and disease Flashcards Preview

Y1 MCD Microbiology > Viral properties and disease > Flashcards

Flashcards in Viral properties and disease Deck (22)
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1

What are general properties of a virus?

Infectious obligate intracellular parasites
Small (20-400nm)
DNA or RNA genome
Requires a host for its replication
Different shapes

2

What are the 5 main stages in the viral life cycle?

1) Attachment to cell surface specific receptor
2) Injection of viral genome into cell and its transfer to the cytoplasm
3) Transcription of viral genome (early regulatory proteins, late structural proteins - cell capsule for when virus is assembled)
4) Genome replicated
5) Virus reassembled and exits cell

3

Explain the parasitic nature of a virus in relation to its host

Virus hijacks hosts DNA/RNA replication machinery
Uses it to synthesis its own proteins which are used to regulate the process
Virus replicates, assembles, exits then colonises the host

4

What is the basis of Baltimore classification and the 7 classes?

Genome type
dsDNA
ssDNA
dsRNA
+sense ssRNA
-sense ssRNA
ssRNA using dsDNA intermediate
ss/dsDNA using ssRNA intermediate

5

What are features of an RNA virus?

Retroviruses
Use reverse transcriptase
Limited in size due to instability

6

What are features of a DNA virus?

Bigger genomes
More accessory genes to help evade host's immune system

7

How are viruses detected?

Genome PCR
Antigen ELISA, IFA
Particle electron microscopy, haemagglutination assay
Cytopathic effect in cultured cells by virus isolation
Antibody detection by serology

8

How is a virus propagated?

Pathogenic virus isolated and grown in human cultured cells to form permissive transformed cells
Cultured virus used to infect monkey cells
Virus acquires mutations to help virus combat new host
Lead to:
-attenuation - weakening of virus
-virus evolves to be stronger against new host cells so is weaker against human cells

9

How is a virus manipulated?

Small viral genomes can be synthesised de novo
Introduced to permissive cells to direct the evolution and produce attenuated disease

10

What are the 8 viral routes of infection (give examples)?

Respiratory - Influenza
Faeco-oral - rotavirus
Contact - herpes
Zoonoses - rabies
Blood - HIV
Sexual - HIV
Maternal - HepB
Germline - retroviruses

11

Define tropism

The preference of viruses to infect certain tissues and not others

12

What 3 factors determine the tropism of a virus?

Susceptibility - receptor interactions
Permissivity - ability to use host to complete replication
Accessibility - whether virus can reach tissue

13

What are the 5 possible outcomes of infection by viruses?

Acute
Persistent
Latent reactivating
Slow
Oncogenesis

14

What characterises acute infection?

Infection→response→quick and complete resolution
Some may not resolve if not treated e.g. smallpox
e.g. flu, rotavirus

15

What characterises persistent infection?

Infection not completely cleared from organism
Low levels of replication and can hide in regenerating tissues
e.g. papillomaviruses in warts

16

What are strategies of persistent infection?

MHC downregulation
CTL escape by mutation
Infection of tissues with low immune surveillance

17

What characterises latent reactivating infection?

Type of persistent infection
Low levels of replication and hide in regenerative tissues
Can't be detected between reactivation periods except for LATs (latency associated transcripts)
e.g. HSV hides in ganglions, re-emerges when there is reduced immune response

18

What characterises slow infection?

Type of persistent infection
Asymptomatic primary infection→long incubation period→slow but relentless progressive course leading to death
Tends to have genetic predisposition
e.g.HIV, SSPE

19

What characterises oncogenesis?

Virus may encode oncogenes
Interference with cell cycle to enhance own replication
e.g. Hep B/C causing hepatocellular carcinoma

20

Define zoonoses

Infectious diseases naturally transmitted between animals and humans e.g.Ebola

21

Define host range

Organisms that can be infected by a disease

22

Give an example of how a virus can emerge and re-emerge

Ebola
cannot infect efficiently so pops up every now and then
transmitted by chimpanzees, bats, civets