Viruses, Viroids, and Prions

Created by holbroha 

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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+

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