Viro - Lecture 3

drraythe's version from 2015-08-30 15:36

Viral Pathogenesis

Question Answer
The majority of viral infxns are ___. Why is this?Subclinical. These are known as subacute or inapparent infxns (asymptomatic). Viruses that severely harm or kill the host self-limit their spread
How do we measure the virulence of a virus?Is its relative level of harm compared to another closely related virus
Explain the course of an acute infxn (think of pic in notes)A single bell curve, w/ the episode of illness & shedding times in the middle of the bell curve
Explain the course of a latent infxn (think of pic in notes)One large bell curve w/ several smaller bell curves. The initial bell curve looks like an acute infxn, & most of the smaller ones do too (shedding & episode of illness at the peak of the curve) but some of the bell curves have no episode of illness portion but ARE still shedding the virus. You also cant detect the virus in the tissues when there isnt a bell curve showing.
Explain the course of a chronic infxn (think of pic in notes)One large bell curve like the acute one (episode of illness & shedding taking place at the peak) but the end of the bell curve continually tapers off throughout the lifetime (the virus is detectable in the tissues) w/ intermittant shedding of the virus w/out clinical signs.
The outcome of the viral infxn depends on many things. Some host factors to consider are...Immune status, genetic background, age, nutrition status, hormonal status
T/F? An acute infxn can recover w/ no residue effects OR it can have residue effects afterT
A chronic infxn is a ____ ____ infxn for (how long?)Silent subclinical infxn for life
A chronic disease might eventually develop into ____Cancer
What are some defenses the respiratory system has against pathogens?The respiratory tract possess sophisticated immune defense mechanisms, as well as non-specific inhibitory mechanisms (ciliated epithelium, mucus secretion, lower temperature) which viruses must overcome
What is the 1⁰ replication site? What can it often determine? The place of 1⁰ replication is where the virus replicates after gaining initial entry into the host. This frequently determines whether the infxn will be localized at the site of entry or spread to become a systemic infxn
What are ways that a dz can systemically spread? (3)(1) Cell to cell contact
(2) Blood stream
(3) CNS through peripheral nerves
What is the 2⁰ replication site? 2⁰ replication takes place at susceptible organs/tissues following systemic spread
What is cell tropism? What is it determined by?Viral affinity for specific body tissues. Can be determined by cell receptors for viruses, Cell transcription factors that recognize viral promoters & enhancer sequences, Ability of the cell to support virus replication, physical barriers, pH, etc
What are the 4 types of infxns a virus can cause? (based on the fate of the host cell) (1) Cytocidal (cell dies)
(2) Persistent, productive ( cant see effect on cell, but - small metabolic disturbance, some cells might lose their special fxns but they can continue to multiply)
(3) persistent, non-productive (usually nil effect on the cell)
(4) Transformation (can turn cell cancerous)
What is a cytopathic effect? Aka CPE - changes you can SEE in the cell
What are the 2 types of viremia? Explain them(1) 1⁰ viremia- when the virus first enters the blood stream for dissemination after entry; the virus is usually in low titers
(2) 2⁰ viremia- has higher viral titer & it is important for transmission of arboviruses & invasion of the CNS (crossing the blood-brain barrier, BBB)
What are the 3 ways cells can respond to viral infxns?(1) No apparent change
(2) Death
(3) Transformation
Direct cell damage & death from viral infxn may result from.. (various things, list some)Diversion of cells energy, shutoff of cell macromolecular synthesis, competition of viral mRNA for cellular ribosomes, competition of viral promoters & transcriptional enhancers for cellular transcriptional factors such as RNA polymerases, & inhibition of the interferon defense mechanisms
INdirect cell damage can result from*INFLAMMATION, integration of the viral genome, host immune response!!
Are inclusion bodies always from viral replication?They are not necessarily direct effect of viral replication; they can be result of altered cell metabolism
How is it that retroviruses can cause persistent infxns (why dont they kill the cell?)Retroviruses do not generally cause cell death, being released from the cell by budding rather than by cell lysis, & therefore can cause persistent infxns
Which type of virus causes fever & increased mucus secretion, & why?Lytic (so usually naked), bc they lyse the cell in order to escape it
What is a Syncytium?A giant cell w/ a bunch of nuclei, usually this is caused by a viral infxn
What is NSP4?Nonstructural protein 4, which is a VIRAL ENTEROTOXIN produced by rotavirus
In what ways can viruses infect the gut?Ingestion, or via the blood
How does a virus cause diarrhea?Diarrhea occurs when the rapid destruction of the epithelial cells causes immature transitional cells to replace them. These cannot carry normal absorptive, resorptive & enzyme secretory functions
Why is viral diarrhea worse in newborns?The disturbance of the osmotic equilibrium is most severe in newborns bc of the constant presence of high concentrations of milk lactose in the intestinal lumen
What happens to intestinal villi during a viral infxn w/ diarrhea?The villi become blunted
What part of the villi do most intestinal viruses target? **Exceptions?Most target the absorptive tip of the villi. The exception is PARVO VIRUS which affects the cells in the crypts (in S phase, so they are growing/replicating), so it takes longer to recover bc that is where repair usually starts
How often is a virus the cause of an upper respiratory infxn?Like >90% of the time.
Respiratory viral infxns cause 3 important changesLocal cessation of cilial beating, local loss of integrity of the overlying mucus layer & multifocal destruction of epithelial cells.
Who does a resp. virus affect most severely, & why?Babies & SMALL animals, bc smaller tubes are easier to plug.
If an animal survives a resp. infxn, what bonus does it have?The new epithelium that lines the airways is a single layer of flat undifferentiated basal epithelium that is resistant to infxn, bc these cells lack viral receptors & are temporarily protected by interferons (cytokines that interfere w/ viral replication) → by the time these are adult resp cells, the hosts adaptive immune response will be able to protect the cells
How can viruses travel to the CNS? What must they overcome to do this?Via nerves or blood vessels. They must pass the BBB (blood brain barrier)
What type of infxn can cause encephalitis, & what are the 3 hallmarks of this?A LYTIC infxn, & the signs are:
(1) Neuronal necrosis
(2) Neuronophagia
(3) Perivascular cuffing (last 2 are caused by the immune response)
Is rabies a lytic infxn?No!
What would cause a CNS infxn w/ no immune reaction? What WOULD be the symptoms?Prions cause slow, progressive neuronal degeneration & vacuolization w/ NO immune reaction
The CNS is a dead end for most viruses, but 2 exceptions would beHerpes & rabies (they are efficiently transmitted from CNS to the periphery to the next host)
Why would a virus really like to infect the lymphoreticular & the hemopoietic system?Infxn of these cells & tissues grant protection to the invading virus from phagocytosis, inflammatory & immunologic inactivation
What is an example of how a viral infxn in the dam can have an INDIRECT effect on the fetus?A prolonged high fever in the dam can cause the fetus to abort, even if the virus has not affected the fetus directly
What is the best bet for a virus to get to the fetus?If it is blood borne & gets through the placenta
If a virus isnt lethal to a fetus, what other bad thing can happen?The virus can be teratogenic
What is a major factor in determining if the fetus will survive the viral infxn?The GESTATIONAL AGE + THE SPECIES MATURATION OF THE IMMUNE SYSTEM. Early infxns usually result in abortion or tolerance, & late infxns mean the fetus' immune system has a chance to fight the virus
Even if the fetus has a well-developed immune system, & it is late in the pregnancy, what can be fatal?The replication is very rapid the fetus can abort, even in late pregnancy
List some respiratory mechanisms of viral sheddingAerosols, droplets, nasal secretions
List some GI mechanisms of viral sheddingSaliva, vomit, feces
List some skin mechanisms of viral sheddingScabs, fluid from vesicles, dander
List some uro-genital mechanisms of viral sheddingUrine, secretions, semen, fluid from vessicles
Milk, blood, & tissues are also mechanisms of viral sheddingYeah, I gave ya that one