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72 terms

Viruses, Viroids, and Prions

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Viruses
obligate intracellular parasites: cannot live outside a cellular host
1 goal of virus
productive infection
Viruses can infect
plants, animals, bacteria
Virus family names end in
-viridae
genus ends in
-virus
viral species
common names...group of viruses with same genetic info and ecological niche (host)
Subspecies are shown by a
number
HIV-1, HIV-2....
Bacteriophages form ____ on a lawn of bacteria
plaques
Animal and plant viruses are grown in a
cell culture maintained from a continuous cell line
Capsomere (viral structure)
protein molecule forming capsid
Capsid (viral structure)
"protein coat" protein shell that surrounds the nucleic acid
Nucleocapsid (viral structure)
nucleic acid plus the capsid
envelope (viral structure)
"viral membrane" phospholipid bilayer with embedded glycoproteins surrounding capsid in enveloped virus
virion (viral structure)
"viral particle" complete infectious viral structure: nucleic acid plus capsid for nonenveloped virus; nucleic acid plus capsid plus envelope for an enveloped virus
viral infections at the apical cell surface
acute infection
viral infection at the basolateral cell surface
systemic
viruses attach to lipid rafts because
reliable for stability
site of release for many viruses
Lytic Cycle
phage causes lysis and death of host cell
lysogenic cycle
prophage DNA incorporated into host DNA
Attachment
viruses attach to cell membrane
Penetration
by endocytosis or fusion.
Uncoating
by viral or host enzymes
Biosynthesis
production of nucleic acid and proteins
Maturation
nucleic acid and capsid proteins assemble
Release
by budding (enveloped viruses) or rupture
acute viral infection
rapid and self limiting
persistent viral infection
long term
latent viral infection
extreme versions of persistent infections
slow or transforming viral infection
complicated types of persistent infections
During the incubation period
virus replicates, host begins to respond
Acute Infections are associated
with epidemics, re-infection, short incubation period,
Immunity from acute infections
if host survived then immune for life.
Antigenic Variation
can cause re-infection as the new structure of the virus is not recognized by the immune system memory
Antigenic Shift
Involves major changes in virion structure due to the acquisition of new genes thru co-infection or recombination
Three Main Entry Points for a Virus
Respiratory System, Digestive Tract, Urogenital Tract
Respiratory Tract
most common portal of entry into the body which is always exposed to large numbers of pathogens
Digestive Tract
second most common portal of entry; the viruses that enter here must be resistant and resilient to harsh environments in order to survive
What causes inflammation of the digestive tract and diarrhea?
destruction of M cells that were used in the transcytosis of the virus
Urogenital Tract
primary point for sexually transmitted viruses to enter the body
What remains in the urogenital tract and causes a local infection?
genital warts
if viruses enter through the eyes
ophthalmic herpess infection
if viruses enter through skin
vector transmission from insects
virus remains in epidermis
localized acute infection
virus gets into the dermis
systemic infection can occur
if viruses enter through the nervous system
some target neurons, some use neurons to get to their preferred target areas
hematogenous dissemination
systemic viral infection taking bloodstream route
viremia
virus replicating in the blood
Transmission within a single species
human to human
Transmission between species
animal to human
viruses transmitted via
fomites/inanimate objects, latrogenic transmission, fecal-oral route
Latrogenic Transmission
transmission via poor techniques employed by health care workers
fetuses exposed to infection
by viremia in pregnant women
Transmission thru respiratory tract
sneeze
Transmission thru the urine
viruria
Transmission thru the urogenital tract
sexual transmission
acute viral infections are seasonal
respiratory...winter
digestive...summer
what inactivate genes responsible for suppressing tumor formation?
retroviruses
______ ________ transform normal cells into cancerous cells.
Activated oncogenes
Characteristics of transformed cancerous cells
increased growth, loss of contact inhibition, tumor specific transplant and T antigens
Viruses associated with human cancers
Epstein-Barr virus, Hepatitis B and C, Human lymphotropic virus, HPV
Prions
proteins normally found on nerve cells (PrPc) Prion protein cellular
Infectious Prions
folded improperly and known as (PrPsc) prion protein scrapie
Scrapie
Sheep
Transmissible Spongiform Encephalopathies (TSE)
diseases caused by prions
PrPsc prions
fibrous structures in the brain called plaque, disrupt the cell membrane causing cell death, convert normal prions to abnormal prions
Prions withstand
cooking, autoclaving, strong alkali treatment, disinfectants,
To inactivate a prion
autoclaving in an alkali solution (bleach containing 2% chlorine) for one hour
TSE
neurodegenerative disease, affects cattle and humans, no test for it, no treatment, no cure
Symptoms of TSE
lack of coordination, staggering, slurred speech, dramatic mood swings, paralysis, death withing a year of symptom onset
Biology of TSE
long incubation period, plaque in brain, no antibody or inflammatory response
Five forms of TSE in humans
Kuru, Creutzfeldt-Jacob Disease (CJD), Variant CJD (vCJD), Gerstmann-Straussler-Scheinker Syndrome (GSS), Fatal Familial Insomnia (FFI)
bans on blood donors
who resided in the UK for 3+ years between 1980-1996, had a blood transfusion in the UK between 1980-present, or resided in Europe for 5+