Mechanisms of Pathogenesis Flashcards
During viral reproduction, there are two different methods of growth:
r- selection
K- selection
What do these terms mean?
r- selection - produce large number of offspring viruses, with no regard to quality. This reproductive method can continue as long as viable hosts continue to be available. Usually acute infections behave like this e.g influenza
K- selection - devote high costs to reproduction, to produce high quality lower number of offspring. Usually because there is a lack of susceptible hosts, or transmission is difficult. Often appear as persistent or latent infections
Why is it difficult for immune system to target the virus HPV?
Resides in dead-skin layer - no capillaries, so no immune cells can access the site of infection
Other viruses can hide in sanctuary sites, or other areas which have reduced immune surveillance
What was the first viral cause of aseptic meningitis?
LCMV
zoonotic infection from rodent urine/ faeces
What clinical sign of viral infection is referred to as “grains of salt on a red background”
Measles - Koplik spots
What are methods that viral nucleic acid can remain latent in a cell?
Maintained as non-replication chromosome in non-dividing cell - e.g neuronal infection in HSV/ VZV
autonomous self-replicating chromosome in a dividing cell
- EBV in B cells as circular episome
- CMV in salivary/ mammary glands and lymphocytes
Virulence is a measure of how likely a virus causes diseases
What is meant by these terms:
Median Lethal Dose
Median Infectious Dose
LD50: Median Lethal Dose: the number of infectious particles that will kill 50% of the infected recipients.
ID50: Median Infectious Dose: the number of infectious particles that will establish an infection in 50% of the challenged recipients.
Virulence is relative, and that the pathogenesis resulting from infection with a single virus strain may vary dramatically depending on the route of infection, as well as on the species, age, gender, and susceptibility of the host
Disease can be due to direct viral damage e.g cell lysis, or immunopathological
What are differences in CD8/ CD4 T cell damage?
CD8 - damages infected cells directly
CD4 - can produce antibodies which form antigen-antibody complexes which can deposited in places such as the kidneys or skin. Can stimulate greater diversity of cytokine activation, and can even cause antibody-mediated enhancement in Dengue
What is mechanism of Dengue antibody mediated enhancement?
Monocytes are not directly susceptible to dengue virus infection.
However, when pre-existing antibodies are present, a second exposure to dengue (for example, with a different serotype), allows for antibody-virus conjugates to bind to Fc receptors (Fc R) on circulating monocytes.
Monocyte infection results in an increase in viral reproduction and a higher risk of severe dengue.
Infected monocytes produce proinflammatory cytokines, which in turn stimualtes T cells to produce more cytokines
What is another term for cytokine storm
SIRS - systemic inflammatory response syndrome
