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53 Cards in this Set
- Front
- Back
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what is virus-host interactions pathogenesis?
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virus entry, spread within the host, cell damage, and transmission
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what is viral pathogenesis?
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the methods by which viruses produce disease
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what are the steps in virus-cell interaction?
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attachment, penetration, uncoating, biosynthesis, assembly, release,
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what are the steps in the virus-host interaction?
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entry (first successful interaction w/host), spread (within host, virus amplification & dissemination), cell damage (consequence of entry, spread, transmission), transmission (virus release into environment)
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what is tropism?
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selective replication of a virus in particular cells or tissues
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what are the determinants of tropism?
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cell receptors/co-receptors & intracellular factors (only present in certain species/cell types)
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what are intracellular factors involved in tropism?
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polymerases and transcription factors needed for biosynthesis, proteases for protein activation
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what does tropism determine?
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species susceptibility & tissue susceptibility
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where can virus entry occur?
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a body surface: respiratory tract, conjunctiva/cornea, alimentary tract, skin, genital tract, urinary tract, placenta/egg
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what is virus entry defined as?
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the first successful interaction of the virus (attachment, penetration, uncoating, etc) with a body surface
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how is skin used as a site of virus entry?
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uncommon portal of entry due to the inert superficial layers of skin (corneum), but disruption by injury, animal/insect bite may allow penetration to suseptible tissue: mucous membranes lack protective covering and are susceptible
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what are examples of viruses that enter through the skin?
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rabies & west nile virus
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how is the respiratory tract used as a site of virus entry?
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most common site of virus entry due to constant inhalation of potentially contaminated air but mucociliary escalaor and alveolar macrophages serve as barriers to entry
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what are examples of viruses that enter through the respiratory tract?
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rhinoviruses, influenza virus, smallpox virus, rubella virus, (sometimes rabies)
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how is the alimentary tract used as a site of virus entry?
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second most common site of virus entry because during swallowing, cells in the mouth, pharynx, esophagus, stomach and intestines are infected, though the esophagus rarely becomes infected due to the tough stratified squamous epithelium and the stomach due to the acid pH, bile and digestive enzymes, but is also protected by intestinal mucus coat
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what are examples of viruses that enter through the alimentary tract?
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poliovirus
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how is the urogenital tract used as a site of virus entry?
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venereal transmission (genital mucosa, semen, seminal fluids)
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how is the placenta used as a site of virus entry?
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infection of fetus by an infected mother
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how is the egg used as a site of virus entry?
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deposition in egg via parental DNA, fertilization by contaminated semen, or egg formation
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how do viruses spread within a host?
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local spread (all) and systemic spread (some)
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what is local spread of a virus?
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cell to cell spread on a body surface
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what is systemic spread?
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spread from body surface to distal organs
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how does local spread occur?
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virus replication/spread on a body surface via sequential infection cell-to-cell facilitated by air and cilia in the respiratory tract, eyelid movement in conjunctiva, and peristalsis in the intestinal tract
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what are examples of viruses that remain localized?
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rhinoviruses, influenza virus, rotavirus
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by what methods can viruses systemicly spread within a host?
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viremic spread and spread via peripheral nerves
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how does systemic spread via viremia occur?
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virus infect epithelium, traverses epithelium, lymphatics, lymph nodes, blood, distal tissues/organs
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what are examples of viruses spread via viremia?
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polio, smallpox, rubella
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how does systemic spread via peripheral nerves occur?
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travel within axon cytoplasm from body surface to reach CNS
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what are examples of viruses spread via peripheral nerves?
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rabies virus, herpesviruses, coronaviruses, flaviviruses
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what determines the cellular response to viral infection?
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differ depending on the virus
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what types of cell injury result from virus replication?
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lytic infection (cell death) & nonlytic infection (absence of cell death)
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lytic and nonlytic infections result in what?
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disease
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what are the mechanisms of virus-induced cell injury in lytic infections?
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depletion of cell components essential for cell life (DNA, RNA, proteins) & apoptosis (programmed cell death induced by virus infection)
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what are the mechanisms of virus-induced cell injury in nonlytic infections?
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altered cell metabolism (partial depletion of cell components), cell transformation (neoplasia), & immune-mediated cell destruction
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In nonlytic infection, what is altered in cell metabolism?
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decreased synthesis of hormones, cytokines, neurotransmitteres, etc which impairs homeostasis
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how does rhinovirus induce cell damage?
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via lytic infection by shuting down of host protein synthesis, respiratory eppithelial cells die, patches of tracheal mucosa become denuded, and sneezing, increased nasal discharge, and nasal obstruction (inflammation)
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how does rabies virus induce cell injury?
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via nonlytic infection by altered cell metabolism: reducing production of neurotransmitters, an unnecessary function of neurons that the body needs to survive
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how does rubella virus induce cell injury?
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via nonlytic infection by altered cell metabolism: impairing cell growth and differentiation during fetal development resulting in congenital defects in brain, eyes, heart, cochlear apparatus
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how does feline leukemia induce cell injury?
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via nonlytic infection by cell transformation (neoplasia)
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how does feline infectious peritonitis induce cell injury?
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via nonlytic infection by immune-mediated destruction of virus infected cells
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what viruses result in nonlytic infection?
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rabies virus, rubella virus, feline leukemai, feline infectious peritonitis
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what is a productive infection?
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virus infection of cells results in production of progeny virus
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what is a nonproductive infection?
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virus infection of cell fails to produce progeny virus (importance: virus persistence, vaccination strategies)
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how can viruses be transmitted?
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shed in respiratory secretions, ocular secretions, saliva (rabies), feces (polio), urine, skin cells (smallpox), semen, milk, blood (west nile)
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what is a permissive cell?
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one that allows complete replication of a given virus and allows a productive infection
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what is a nonpermissive cell?
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one that blocks virus replication at some point
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what are the characteristics of rhinovirus?
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respiratory tract, local, respiratory secretions, lytic
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what are the characteristics of influenza?
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respiratory tract, local, respiratory secretions, lytic
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what are the characteristics of smallpox?
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respiratory tract, systemic lymph/blood, skin/respiratory secretions, lytic
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what are the characteristics of poliomyelitis?
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alimentary tract, systemic lymph/blood, feces, lytic
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what are the characteristics of west nile encephalitis?
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skin, systemic lymph/blood, blood (mosquito), lytic
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what are the characteristics of rabies virus?
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skin, systemic (nerves), saliva, unknown
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what are the characteristics of rubella virus?
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respiratory tract & placenta, systemic lymph/blood, respiratory secretions, altered cell metabolism
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