Pathophysiology of viral infection Flashcards
(39 cards)
What is the Ro
- how many new infections one person will generate during their infectious period
- approximate
- vary by outbreak, mode of transmission and location
Give an example of a virus that harms a particular group of the population
Describe it
ZIKA Virus
- it causes birth defects (microcephaly) in babies born to some infected mothers
- microcephaly is underdeveloped heads and brain damage
- its also associated to guillain-barre syndrome: the immune system attacks the nerves
- transmitted via mosquitoes
What is a virus?
+ structure, size, MOA
- particle containing nucleic acid and a protein coat +/- envelope
- small in size (100x smaller than somatic cells, 10-400nm)
- obligate intracellular- only replicate inside living cells
- can infect range of organisms: humans, animals, plants, bacteria
How can the nucleic acid in viruses be described?
- DNA or RNA
- ds or ss
- +ve/-ve/ambisense
What is a nucleocapsid?
= nucleic acid + protein coat
What is a virion?
= complete intact virus particle (the physical particle in the extracellular phase which is able to spread to new host cells)
Briefly outline the tasks a virus must do in order to grow
- identify which cells to enter and how
- know how to replicate inside the host cell
- know how to exit and move between host cells as well as to a new host to persist in nature
- develop mechanisms to evade host defences
Outline the stages involved in pathogenesis
- encounter: virus meets host
- entry: virus enters host
- multiplication: virus replicates in host
- spread: virus spreads from site of entry
- damage: due to the virus itself, the host response or both
- outcome: host or virus wins, or coexist
How can viruses enter the body through the skin?
- abrasions
- insect/animal bites
- needle punctures
Gastroenteritis viruses enter via alimentary tract
What makes this tract a hostile environment?
- extreme acidity/alkalinity
- digestive enzymes
What makes the urogenital tract a hostile environment?
How can viruses enter?
Give an example of a urogenital tract virus which causes local infection, and one which causes systemic infection
Low pH
- via mucous membranes
- abrasions
Local- HPV
Systemic- HIV
How might localise infection of the eye present?
And viral spread?
- conjunctivitis
- Eye blindness/CNS
Describe the baltimore system for viral classification
- By knowing the nature of a viral genome we can understand the steps it must take to produce mRNA needed to make viral proteins
- identifies 7 pathways to creating mRNA
https://www.virology.ws/2009/08/12/simplifying-virus-classification-the-baltimore-system/
What happens after a virus replicates at the site of infection?
- Some remain localised within epithelium/within one system
- some cause disseminated infection: inflammation compromises integrity of cell basement membrane
What does apical viral release and basolateral release mean?
Give examples
Apical
- facilitate viral dispersal but not into underlying tissues
- e.g. flu
Basolateral
- provides access to underlying tissues and can facilitate systemic spread
- e.g. rabies
Give 4 methods viruses can enter blood
What does this mean for spread?
- Directly through capillaries
- By replicating in endothelial cells
- Through vector bite
- By lymphatic capillaries
Virus now has access to most tissues
What is primary/secondary viraemia?
Primary viraemia: This is when the virus enters the bloodstream (from inital site of infection).
Secondary viraemia: This is when viraemia has caused an infection in another organ or tissue by spreading through the bloodstream.
What is passive/active viraemia?
- Passive: viral entry into blood without active viral replication as in mosquito inoculation
- Active: viral entry into blood following replication in site of infection and release via basolateral membrane e.g. measles
How can viraemia be of diagnostic value?
How can it be a practical problem?
- Used to measure viral replication/density
- Means we need to screen blood donors
Describe neural spread of viruses
- less common than haematogenous spread
- can go from periphery to CNS or vice versa
Consider neural spread of viruses
What do the following terms mean?
a. Neurotropic
b. Neuroinvasive
c. Neurovirulent
a. virus can infect neural cells
b. virus can enter CNS from peripheral sites
c. virus can cause disease of nervous tissue
Describe the following viruses in terms of neuroinvasiveness and neurovirulence
a. HSV
b. Mumps
c. Rabies
a. Neuroinvasiveness: +
Neurovirulent: ++++
b. Neuroinvasiveness: ++++
Neurovirulent: +
c. Neuroinvasiveness: ++++
Neurovirulent: ++++
What is tissue tropism?
- the cells/ tissues which support growth of a pathogen
- can be limited or pantropic
What are the determinants of tropism?
- Cell receptors: e.g. HIV required CD4+
- Cellular proteins that regulate viral transcription e.g. John Cunningham (JC) virus requires viral enhacers in oligodendrocytes
- Cell proteases e.g. flu requires serine protease
