mechanism of viral infection

Question 1

common virus disease of man

Answer 1

flu 
common cold 
measels 
mumps 
RSV 
covid 19 
chicken pox

Question 2

general patterns of viral infection

Answer 2

acute infection = huge spectrum of disease and range of outcomes. resolution by immunity

latent, reactivating infection = mainly caused by herpes viruses
persistent infection = HIV, HCV, measels

Question 3

congenital rubella

Answer 3

persistent infection, if infected in utero, virus is seen as self, baby is born immunotolerant and virus continues to replicate in neonatal tissues

Question 4

how does virus infection of a host lead to disease?

Answer 4

pathogenesis results from cell and tissue damage caused by viral infection. on most occassion damage is limited by hosts immune system
some occassion, relative limited damage caused by virus made worse by host immune system = immunology

Question 5

inapparent infections

Answer 5

90% of all poliovirus are asymptomatic
many get infected with parainfluenza 5 without clear symptoms
requires virus be non cytopathic and host adapted

Question 6

hepatits c virus

Answer 6

chronic hepatitis = disease of severe liver damage and loss of hepatocytes. caused by persistent HCV infection

HCV = non cytopathic
associated with extensive liver infiltration of leukocytes
proinflammatory cytokine levels v high
viral clearance and disease associated with generation and infiltration of CD8 cells which atttack infected cells and destroy them
HCV persistence associated with gen of HCVA variants that arent recognised by cd8 cells

Question 7

dengue fever

Answer 7

most common mosquito borne infection
case fatality rate from severe dengue = 1-5%
4 serotypes = all have same clinical manifestations = fever, abdominal. pain, headache, rash

Question 8

immunopathology of dengue

Answer 8

dengue shock syndrome and hemorrhage
antibodies form in response to dengue infection = dont cross protective against other subtypes of virus. result in more severe disease due to antibody-dependent enhancement
non neutralising antibodies coat virus. internalised into mononuclear phagocytes through fc receptors = fixation of complement by ciruclating immune complexes resulting in release of productions of complement cascading leading to increased vascular permeability, shock and death

Question 9

RSV and immunopathology

Answer 9

in early life show unbalanced th1/2 responses
depresses inflammatory cytokine production, cd8+ response and igG production = clearance slow and development of memory is poor
enhaces igE production, leading to allergy/asthma on reexposure

Question 10

seasonal influenza vaccine

Answer 10

tetravalent

Question 11

immune response to flu

Answer 11

antigenic drift = antigens on virus change
we make neutralising antibodies against last infection
make t cell response against last infection = should be effective against next infection
due to antigenic drift, vaccines dont always help if we dont know whats coming