virus of causes of disease Flashcards
define virus
An infectious, obligate intracellular parasite
Comprising genetic material
(DNA or RNA) surrounded by aprotein coat and/or a membrane
define a viron and its structure
When not inside an infected cell, viruses exist as virions. These consist of:
Genetic material (DNA or RNA)
Protein coat (capsid)
Virions can exist outside of a host for a variable amount of time (depending on the virus and the environment), but cannot replicate unless they are within a host
i.e. Obligate intracellular – totally dependant on living cells for their replication and existence
All have a receptor binding protein to “dock” to cells
All contain genetic material
name some ways in which viruses are not considered alive.
- do not feed
- do not respire
- cannot reproduce independamtly
- no cell wall
- no organelles
what are the different shapes of a virus?
- complex
- helical
- icosahedral
outline the process of how viruses replicate?
- virus attachment to specific receptor on the host cell
- enters the host cell - uncoating of viron within cell - only central core carrying nucleic acid and associated proteins anter the host cell
- migration of the viral genome to the host cells nucleus then transcription to mRNA using host materials
- translation of viral mRNA to produce structural proteins, viral genome, non-structural proteins eg enzymes
- assembaly of viron (occurs at different locations in the host cell depending on the virus)
- release of new virus particles via budding / exocytosis and host cell death
outline the diffeent ways that viruses cause disease.
- host cell lysis
- modification of host cell:
e.g. rotavirus - atrophies villi and flattens epithelial cells:
decreases small intestine surface area
nutrients incl. sugar not absorbed
hyperosmotic state
profuse diarrhoea - overactivity of immune system
- damage through cell proliferation:
e.g. human papillomavirus - cervical cancer - evasion of host defences:
antigenic variability
prevention of host cells apoptosis
downreg of intracellular hosts defence proteins
interference with host cells antigen processing pathways
name some common viruses.
Miscarriage and birth defects:
- Cytomegalovirus (CMV),
- Varicella Zoster Virus (VZV),
- Herpes Simplex Virus (HSV),
- Rubella
Cancer:
- Epstein Barr Virus (EBV) - lymphoma
- Hepatitis B/C - hepatocellular carcinoma
- Human Papilloma Virus (HPV) - cervical/anal cancer
- HIV - many!!!
Outbreaks
- influenza
- measles
- mumps
- norovirus
- SARS,CoV-2
Immunosuppressed patients
Reactivation of latent viruses causing end organ damage:
- hepatitis
- retinitis
- haemorrhagic cystitis
- encephalitis
- pneumonitis
why is it clinically importamt to recognise how viruses cause disease?
- Understand transmission and natural history
- Know who is most at risk
- Develop treatments and “preventative” drugs
Viruses vary wildly in therange of clinical syndromes they can cause, what is this down to?
- Different host cells and tissues that they can infect
- Different methods of interaction with the host cell
Describe the basic properties of a virus (protein coat, cell receptor, nucleic acid, RNA-based or DNA-based giving salient examples.
protein coat - capsid:
- encases the viral nucleic acid
nucleic acid:
- either DNA or RNA but never both
- single stranded or double stranded
- linear or circular
- segmented or non-degmented
cell receptor binding:
- viruses attach to specific cell receptors on the host cell
outline the difference in the stability of the virus based on their nucleic material.
RNA - higher mutation rates ue to lack of proofreading by rna-dependant rna polymerase
DNA - generally more stable with fewer mutations
