Viral properties and disease Flashcards
Nature, life cycle, parasitic nature; Classification; detection, cultivation, manipulation; Viral routes of infection; Viral infection outcomes; Zoonoses
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
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?
Genome type dsDNA ssDNA dsRNA \+sense ssRNA -sense ssRNA ssRNA using dsDNA intermediate ss/dsDNA using ssRNA intermediate
What are features of an RNA virus?
Retroviruses
Use reverse transcriptase
Limited in size due to instability
What are features of a DNA virus?
Bigger genomes
More accessory genes to help evade host’s immune system
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
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
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
Define tropism
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?
Acute Persistent Latent reactivating Slow Oncogenesis
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
