Lecture 2 Flashcards
RNA viruses
Must encode or carry RNA-dependent RNA polymerase
Replicate in cytoplasm
Often have faster mutation rates than DNA viruses
DNA Viruses
Viral genomes stable in cell (persistent infections)
Most occupy nucleus
Temporal control of viral gene expression
Virulence factors (virus-encoded activities)
enhance attachment, transmission, replication, evasion of host responses
Attenuated virus – loss of virulence factors
Stages of Viral Infections
Acquisition – gain access to body
Initiate primary site infection (often oral or respiratory)
Innate immune response activated (Phagocytes, IFN response)
Incubation period
Spread to secondary site in some cases
Replication in target tissue
Trigger adaptive immune responses
Can be beneficial or develop into immunopathology
Resolution or persistence
Stages of viral Infection part 2
Asymptomatic – can progress to 2° site without symptoms
Prodrome – early, non-specific symptoms
(fever, aches, chills) (what is causing the symptoms of prodrome?)
Immune Response – innate immunity can usually resolve; if not, adaptive immune responses are triggered
Convalescence – symptoms from tissue repair mechanisms; development of immunological memory
Viral transmission
Inhalation (most common route of entry)
Preferentially infect oral & respiratory mucosa
epithelial cells express viral receptors
possess necessary replication machinery
Gastrointestinal
virus shed in feces (fecal-oral)
M cells in Peyer’s patches
Sexual
Blood
Transcutaneous
Maternal (fetal/neonatal)
Viral Transmissions pt 2
Various mechanisms of dissemination from 1° site
local spread
Viremia – in the bloodstream
Within infected leukocytes & lymphocytes
M cells
Into the CNS
Viremia to CSF or meninges, by macrophage migration, or by transmission from infected PNS neurons
Abortive is
failed infection
Inapparent
asymptomatic (no consequences)
lytic
infection kills host cells
non-lytic (persistent)
infection does not result in cell death
Chronic
non-lytic, productive
Latent
non-productive
Recurrent
on/off production
Transforming
immortalizing
Permissive
– allow complete replicative cycle
semi-permissive
slow, inefficient replication
Non-permissive
-lack essential machinery or actively block replication or assembly
Slide 10 review it
Lytic infections do what?
KILL TARGET CELLS
Produce Cytopathic Effects (CPEs) – induce morphological changes
Inflict damage
Inhibit repair
Inhibit DNA & protein synthesis
Degrade host nucleic acids
Disrupt host cellular functions
Non-Lytic Infections
Viruses persist intracellularly
(released through exocytosis or budding)
Occur following infection of non-permissive cell where virus can’t replicate
Viral gene products transform cells
-incorporation into host nucleus – disrupt growth regulation
-oncogenic transformation – promote unregulated growth (15% of cancers related to viral oncogenes)
Host Defenses
-Innate immune responses
-detection of viral nucleic acids
1)TLRs
2)RLRs
-cytokine release
-IFN response
-Immune cell activation (macrophages, dendritic & NK cells)
-Adaptive immune responses
-Antibody-mediated immunity
especially for cytolytic viruses & any viremia
-T cell-mediated immunity
Interferon Response
-Critical for defense against viruses
-TLRs detect both ssRNA and dsRNA in endosomes
-RLRs detect RNA in the cytoplasm
Host Defenses
Two pathways induced by IFN interfere with viral RNA being translated into protein
Most common viral diseases are
-common cold
-influenza
-flulike syndromes
-gastroenteritis
Determinants of viral diseases are
-exposure/entry
-viral dose
-target tissue/tissue tropism
-permissiveness of cells
-host status (age, immunity, health)
-viral structure (naked vs. envelope)
slide 21 lists out the remaining viral diseases
Immune evasion does what?
inhibit IFN response
modification of viral antigens
cell-cell spreading (syncytia)
suppress antigen presentation
inhibition of lymphocytes
T/F: The immune system is a major contributor to disease or symptoms caused by some viral infection
dis bish true
Flu-like systemic symptoms are called what?
prondrome
Type IV hypersensitivity reactions are what?
reaction mediated by effector T cells
Type III hypersensitivity reactions are what?
IgG antibody-antigen deposits forming in small vessels and alveoli
Hepatitis B virus
Hepatitis B
Immune-mediated mechanisms
-CD8+ T cells
-Antibody
Flavivirus (dengue)
Hemorrhagic fever
Immune-mediated mechanisms
-Immune Complexes
-T cells
Paramyxovirus (RSV)
Bronchiolitis
Immune-mediated mechanisms
-CD8+ T cells
-Antibody
Arenavirus
Choriomeningitis
Immune-mediated mechanisms
-CD8+ T cells
