Flashcards in Viral properties and disease Deck (22)
What are general properties of a virus?
Infectious obligate intracellular parasites
DNA or RNA genome
Requires a host for its replication
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
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
What is the basis of Baltimore classification and the 7 classes?
ssRNA using dsDNA intermediate
ss/dsDNA using ssRNA intermediate
What are features of an RNA virus?
Use reverse transcriptase
Limited in size due to instability
What are features of a DNA virus?
More accessory genes to help evade host's immune system
How are viruses detected?
Antigen ELISA, IFA
Particle electron microscopy, haemagglutination assay
Cytopathic effect in cultured cells by virus isolation
Antibody detection by serology
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
-attenuation - weakening of virus
-virus evolves to be stronger against new host cells so is weaker against human cells
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
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
The preference of viruses to infect certain tissues and not others
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
What are the 5 possible outcomes of infection by viruses?
What characterises acute infection?
Infection→response→quick and complete resolution
Some may not resolve if not treated e.g. smallpox
e.g. flu, rotavirus
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
What are strategies of persistent infection?
CTL escape by mutation
Infection of tissues with low immune surveillance
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
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
What characterises oncogenesis?
Virus may encode oncogenes
Interference with cell cycle to enhance own replication
e.g. Hep B/C causing hepatocellular carcinoma
Infectious diseases naturally transmitted between animals and humans e.g.Ebola
Define host range
Organisms that can be infected by a disease