2: Viruses 1 Flashcards
describe some important differences between bacteria and viruses
viruses:
-most intracellular (cell-mediated response)
-Abs help prevent dissemination from local site
-use host machinery to replicate
-RNA, DNA, or Retrovirus
-nearly all contagious (no normal flora)
-don’t need preceding pathology to be infectious*
-damage from immune response (local- 72h, spread- wks)
(incubation related to mechanism of disease)
*exceptions: CMV, a few others
four features of viral pathology
- lymphocytic infiltrate generally around blood vessels
- inclusion bodies
- cytopathic
- viral replication
- immune response
- syncytia
three general mechanisms of viral diseases
- local disease
- hematogenous dissemination
- transmission through nerves
mechanism of viral damage to host cells
- enter cell and replicate at the host’s expense
- in many viral diseases, damage mediated by host immune response to virus rather than viral cytotoxicity
describe viral tropisms for the following:
- HIV
- EBV
- rabies
- rhinovirus
- HIV: CD4
- EBV: complement CD21 on macrophages - then infects lymph nodes and B cells
- rabies: AChR
- rhinoviruses: ICAM-1
basic steps in viral infection and replication
- attachment to host cell
- host cell penetration
- viral uncoating
- replication
- re-assembly of virions
classic immune response to viruses
not pyogenic - so lymphocytes, macrophages, plasma cells
hallmarks of viral illness
- infection of mucosal cells or parenchymal cells at site of entry
- dissemination via viremia
- lymphocytic inflammation +/- necrosis
- morphologic alterations of infected cells (vacuolization, inclusion bodies, multinucleated cells, etc.)
why is chicken pox worse as an adult than as a kid?
as a kid- classic picture of chicken pox
as an adult - encephalitis or pneumonitis
antiviral function of antibodies
neutralizing rather than functional in tissue responses
-prevent re-infection, but often too late to limit dissemination of current infection
role of antibody in viral disease states
immune complex reactions - arthralgias, glomerulonephritis
-may enhance cell uptake and promote infection
cell mediated responses to viral infection
- lysis of infected cells, mediated by CD8 + MHC1
- dependent on CD4 for initial reaction
- also NK cells on cells w/ decreased MHC1 expression
induction of antiviral cytokines as a part of cell mediated response to viral infection
- secretion of gamma-IFNs: inhibit RNA translation, which affects viral translation more than host functions
- IFN-a and IFN-b: activation of antiviral responses
two main patterns of viral illness:
- local illness (rhinitis, flu, gastroenteritis)
- short incubation time (d)
- lesion at site of entry (local cytopathic injury + inflam) - distant illness (organ-specific, systemic)
- longer incubation times (w)
- viremia
- pass along nerves
- lesions involve immune-mediated damage
what does the incubation period of a viral illness tell you?
reflects distribution of virus
- proliferation at sites of entry
- viremia - hematogenous dissemination systemically
- lymphoid dissemination (HIV, EBV)
- transmission along nerves (herpes, rabies)
symptoms may reflect development of host immune response
