Lecture 13 Very basic introduction to classical viral pathogenesis and virus pathology Flashcards
Do viruses infect cells or tissues?
Viruses infect cell to cell but need pathways to infect the organism- needs a way in, a method of movement, and a way out.
Where can the virus enter the host?
Respiratory
Gastrointestinal*
Blood borne
Arthropod-mediated
Sexual
* Includes Peyer’s patches or “gut-associated lymphoid tissue”
How does the virus infect the bloodstream?
Passively, or associated with
infected blood cells (e.g. Hepatitis B, Hepatitis C)
How does the virus infect the Lymphatic system?
Entry to lymphatic system: From gut via Peyer’s patches (e.g. Polio virus). After exiting respiratory epithelium (e.g. Measles virus)
what is more common: target cell type or target organ?
target cell type
What are the target cell type for HIV?
T- helper cells
Does a virus when passing the bloodstream prefer the distal or apical side?
apical (inside)
What is the difference between the way the virus infects unicellular organisms vs. mutlicelluular organisms?
Unicellular: only need to enter the host cell in order to replicate.
Multicellular: must find a way to enter not just the cell but also the organism (animal), then get out again.
Disease is a common result of infection though to necessarily so (infection may be entirely asymptomatic depending on host’s genetics, health status, immune status).
How does the virus infect the nervous system?
HSV, rabies
Describe virus dissemination within the host.
After replicating, initially at the site of infection virus may disseminate to preferred site of replication (target organ) via the bloodstream, lymphatic system, and nervous system.
Describe the virus dissemination of measles
Initial site of infection = respiratory epithelium (replication for 2-4 days at this local site).
Spreads through draining lymph nodes
Enters blood infected monocytes = full dissemination
Target organ = skin
What is the target cell-type of HIV?
Primary infection may be macrophages in local tissues at the site of infection. Macrophages may then enter the lymph. In lymphatic system, HIV encounters and infects its target cell-type (The cells) that can then be carried throughout the body and or collect in lymph nodes (target organ).
Then:
Virus replicates to high levels within the target organ or target cell and symptoms of disease generally arise from higher virus load in the target organ. The figure shows gradual depletion of target cell type during HIV chronic infection as virus titer gradually rises with a burst oat the end due to extreme immune degradation.
