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96 Cards in this Set
- Front
- Back
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Dimitri Iwanowsk |
Russian botanist - mosaic tobacco |
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Walter Reed |
Yellow Fever |
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Fredrick Twort & Felix D'Herelle |
Bacteriophage |
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What happened in 1931 |
Electron microscopes allow the observation of Viruses |
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What is a Virus |
Genetic elements that replicate independently of the host's chromosome but not independently of the cells themselves |
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Characteristics of Viruses |
- Either DNA or RNA, double or single stranded genomes - no cytoplasmic membrane - no Cytosol - no organelles - Outermost layer provides protection and recognition sites for host cells ** Cannot carry out metabolic pathways or replicate in absence of host cell |
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Extracellular State |
Virion |
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Intracellular State |
Capsid removed - exist as a nucleic acid |
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Naked Viron |
Only nucleic Acid and Proteins are present - Called nucleocapsid |
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Nucleocapsid |
Naked viron - only nucleic acid and protein are present |
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Capsid |
Protects the genome Gives shape to virus Made up of protein subunits called Capsomeres Organization of capsomeres give viruses symmetry Involved in the attachment of the host cell |
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Capsomeres |
Protein subunit of a capsid Number of capsomeres is a characteristic for specific virus |
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Herpes Virus |
162 Capsomeres |
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Adenovirus |
252 Capsomeres |
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All viruses have |
NUCLEOCAPSID |
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Enveloped Virus |
Acquired from host cells during viral replication or release |
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Envelope is a |
Portion of membrane system of host but not function of cytoplasmic membrane ei: endocytosis etc |
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Envelope is composed of |
Phospholipid bilayer and proteins |
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Envelopes proteins and glycoproteins |
Play a role in host recognition |
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Enveloped Virus with helical Capsid Model |
Helical Capsid Matrix Protein Envelope Glyco proteins |
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3 shapes of Viruses |
Helical Polyhedral Complex |
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Viral Taxonomy and Classification |
Not classified using hierarchical system due to relationship between viruses are not well understood - Names derived from characteristics - Based on: Genome, shape, presence of envelope and size of virion |
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Class of Virus and Genome |
DNA: ss DNA/ds DNA RNA: ssRNA/ dsRNA RNA&DNA: ssRNA (retroviruses)/dsDNA(hepadnaviruses) |
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Replication of viruses |
Dependent of host enzymes and organelles to produce new virions - Lack gene for all the enzymes needed to replicate - Lack ribosomes for protein synthesis |
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Lytic |
Replication cycle results in death and lysis of host cell |
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Lysogenic |
a dormant state within the host |
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Viral replication steps |
Attachment Entry Biosynthesis Assembly Release of assembled particles |
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Attachment |
Uses tail pins and legs to attach to the surface of the outer membrane |
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Entry |
Sends a string of T4 genome down through outer membrane, peptidoglycan and cytoplasmic membrane |
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How it looks |
Capsid head full of DNA, Sheath leading down (body), Tail fibers (look like legs), Base plate and pins leading out of it |
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Viral Replication During Lytic Cycle time map |
attachment:0 Entry:5 mins Synthesis and assembly : 5-25 min. Burst time: @25mins Release of virons by lysis: 25-27~mins |
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Lysogeny |
aka Lysogenic cycle or temperate phage modified replication cycle infected host cells grow and reproduce normally for generations before they lyse |
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Prophage |
Inactive Phage - viral genome incorporated into host genome but viral proteins are not actively being produced |
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Transduction |
When phages transfer bacterial DNA that has been incorporated into phage genome into infected host cells. - one of the mechanisms of horizontal gene transfer |
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Animal Viruses VS Bacteriophage |
Same basic replication pathway as bateriophage Differences in attachment/entry,release, and site of replication - differences result from: Envelope around some viruses and the Eukaryotic nature of animal cells (lack cell walls) |
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Attachment of Animal Viruses |
Attachement of animal viruses - utilizes specific ligand - receptor interactions - do NOT have tails or tail fibers - have glycoprotein spikes or other attachment molecules that mediate attachment |
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Surface receptors of Animal Viruses |
Look like spikes on viral surface Enzymes like the neuraminidase- essential in viral maturation and budding |
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Hemagglutinin |
Plays a key role in adsorption and penetration of the host |
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Three mechanisms of entry |
1. Direct penetration - capsid stick into membrane and sends out a viral genome ei: poliovirus (naked) 2. Membrane Fusion - Glyco protein fuses to cell membrane and enzyme breaks down the bottom part that touches then a viral genome is released by the uncoating capsid ei:HIV (enveloped) 3. Endocytosis - whole virus is engulfed then its membrane is broken down and the enveloped virus is released, uncoated then viral genome is released ei: Influenza (evveloped) |
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Synthesis of Animal Viruses |
- each type requires different strategy depending on its nucleic acid - DNA often enters the nucleus - RNA often replicate in cytoplasm |
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Positive single strand RNA acts like: |
mRNA |
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Synthesis of dsDNA virus of animals |
dsDNA viruses - similar to replication of host cellular DNA, viral genome replicated in the nucleus and the viral proteins made in the cytoplasm |
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Synthesis of ssDNA |
Cells do not use ssDNA parvoviruses have ssDNA genome - host enzymes produce DNA strand complementary to viral genome to form dsDNA molecule dsDNA used for viral replication and transcription |
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most DNA viruses enter: |
in nucleus and assembled in cytoplasm |
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most RNA viruses develop |
solely in cytoplasm |
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Naked Viruses are released by: |
Exocytosis or lysis |
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Enveloped viruses cause: |
Persistant infections - years with no activity |
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Latent virus/provirus |
Animal viruses that remain dormant in host cell - may be years with no viral activity - typical of enveloped viruses - differences from lysogeny of bacteriophage - some latent viruses do not become incorportated into chormosome - incorporation of provirus into host DNA is rpemanent no induction in eukaryote (HIV) |
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Retrovirus |
RNA virus do NOT use their genomes as mRNA carry its enzyme called Reverse Transcriptase that use viral NA to synthesize single stranded DNA DNA used as template to for a complementary DNA strand by DNA polymerase - forms double stranded DNA dsDNA mirgrates into nucleus and is incorporated into host genome by another retrovirus enzyme called an Integrase |
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Integrase |
Retrovirus enzyme |
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Retrovirus migration |
Double stranded DNA migrates into cell nucleus and integrates into host cell genomic DNA (provirus) - VIRAL DNA IS PERMANENTLY INCORPORATED INTO HOST DNA ei: HIV |
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Epidemiology of Aids |
First recognized in homo men in USA Now world wide Found in blood, semen, saliva, and vagina secretions and breast milk - Blood and semen most infective - infected fluid must be injected or contact a tear in the skin or mucous membrane |
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HIV Target Cells |
target white blood cells - CD4 aka helper T cell death by - killing via virus induced cyto-lysis - killing of infected cells by HIV specific CD8 killer T cells CD4 are key immune cells and depletion impairs function of the immune system |
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Most deaths due to AIDS are actually due to |
Mycoses - infection with various fungi partly define end stage AIDS - pnumonea indicative of end stage of AIDS |
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Treatment for enveloped positive ssRNA viruses with Reverse Transcriptase |
Cocktail of antiviral drugs - does not cure infection but can reduce viral load to undetectable levels and patient can live normal life while on treatment |
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Potential outcome of Host cell interaction and Viral infection |
- cell destruction and necrosis - No cell destruction - latent infection - Tumor transformation |
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Viruses are repsonsible for % of human cancers |
20-25% |
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Cancer |
The uncontrolled reproduction of cells result in the formation of a tumour - Benign - not cancerous - Malignant - Cells multiply too quickly and spread all over the body - metastasis |
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Cancer causing Viruses |
Herpes - cervical Epstein Barr - lymphoma - tumour of Jaw HPV - cervical Human T cell - Leukemia |
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Oncogene Theory |
- Cancer causing genes are in DNA in inactive form - found in a veriety of organisms - proto-oncogenes function in regulating growth and cellular devision - Converted to oncogenes by carcinogens: virus radiation and chemicals - oncogenes present in certain viruses and can cause cancer when incorporated into host cell |
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Virus Killing Cancer Cells |
2015 - first approved - genetically engineered Herpes simplex Virus type 1. - produces a granulocyte-macrophage colony - stimulating factor - cytokine that recruits immune system to tumour site - used for localized treatment of unresponsive/inoperable skin melanomas |
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How does IMLYGIC work |
Targets and replicates within tumor cell Causes cell lysis or death which ruptures tumours releasing tumour derived antigen which may promote an antitumour immune response |
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PRION |
infectious protein - Transmissible spongiform encephalopathies (TSE) - Normal cellular prion protein (PrPc) are present in all uninfected brains - abnormal prion found in infected brain PrPsc |
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How Prion disease works |
Caused my misfolding of proteins. Spread when PrPsc interacts with normal PrP and causes it to adopt the incorrectly folded state. This continues until all PrP are in the PrPsc form sprial to straight* |
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What happens in the brain from Prions |
- PrPsc are very resistant to chemicals - clump together - taken up by lysosomes - cant break it down so it bursts the cell leaving lesions in the brain tissue - free mutants are taken up by other cells and the cycle continues |
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Resevoirs of infection and 3 types |
Site where pathogens are maintained as a source of infection - Animal Reservoir - Human Carriers - Nonliving Reservoir |
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Animal reservoir |
Zoonoses: disease naturally spread from animal host to human - Direct contact with animal or its waste - eating animals - bloodsucking arthropods humans are dead end host for zoonotic pathogens |
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Human Carriers |
- infected but asymptomatic and can infect others - Some can eventually get sick but some never do Healthy carriers may have a defensive system that protects them ei: TB, AIDS |
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Non Living reservoir |
Soil, water and food - some may be contaminated due to feces or urine - E coli |
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Emerging viruses |
Viruses that appear for the first time in a population or has rapidly expanded its host range ei: Zika, West Nile, Ebola, SARS |
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Hemorrhagic Fevers |
Enveloped, unsegmented Negative ssRNA Viruses - Marburg and Ebola virus are causes Natrual resevoir and mode of trasmission to humans is unknown - spread from person to person from contamination - Virons attack many cells of the body * Macrophages and liver cells - uncontrolled bleeding under skin and from every body opening - up to 90% die - Only treatment: Fluid replacement |
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Ebola |
Largest in history - west africa - first case reported in March 2014 - Outbreak over March 29 2016 |
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Ebola Pathology |
- Enters patient through mucous membrane, breaks in the skin or parenterally - infects: monocytes, macrophages, dendritic cells, epithelial cells, endothelial cells, fibroblasts, hepatocytes and andrenal cortical cells - Incubation period - 6 days injection/10 days contact - fatality 70%; 61% if hospitalized |
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Ebola Treatment |
- No treatment - Clinical management = supportive care of complications - Recommended care: volume repletion, maintenance of BP, nutritional support |
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Zmapp |
Ebola experimental treatment - intravenous cocktail with 3 humanized monoclonal antibodies - targets surface of glycoproteins on virus and prevents attachment - worked in 5/7 ppl but not sig. enough |
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TKM |
Experimental Ebola treatment - interfering RNA that targets 3 of 7 Ebola proteins - RNA targets viral RNA for degradation in the cell |
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Merck Vaccine |
developed in Canada - live virus that expresses the ebola surgace glycoprotein - works with 100% efficiency |
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Flu virus is called |
Orthomyxoviridae |
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Viruses that infect animals but transfer to humans |
Bunyaviridae and Arenaviridea |
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Influenza |
Caused by orthomyxovirus A and B - rarely attacks cells outside the lungs - 8 different ssRNA molecules - envelope studded with two glycoproteins - nuraminidase(NA): enables viral release by hydrolyzing sialic acid residues from surface - Hemagglutinin(HA): binds to terminal sialic acid, attachmet to pulmonary epithelial cells trigger endocytosis of virus |
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Nueraminidase(NA) |
- One of main surgace antigens on influenza virus - inhibition of enzyme prevents viral maturation |
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Antigenic drift |
Mutation |
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Antigenic Shift |
recombination |
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Mutation |
Antigenic Drift |
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Recombination |
Antigenic shift |
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Influenza mutations |
Result in new strains of influenza virus - often in Asia due to dense pop and domesticated birds and pigs |
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Influenza and the world |
New pandemic could involve 1/3 of worlds population viruses multiply in epithelial cell lining in the lung - death of infected cells eliminate the lungs epithelial lining - patients more susceptible to secondary bacterial infections |
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Epidemiology of Influenza |
- infection primarily through inhalation of airborne viruses - millions infected in US yearly - about 64,000 die anually |
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Prevention and Treatment of Influenza |
Treatment: Oseltamivir- blocks virion release from infected cells - must be administered within 48hrs Prevention: - Immunization |
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Zika Virus infection methods |
- Transmitted by mosquitos bites, and sexual contact with someone infected - Viral RNA can be found in saliva, breast milk and urine. - unclear if these can cause infection - in semen up to 76 days post infection |
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Flavivirus |
Suspected host for Zika is non human primate |
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Zika structure |
Enveloped virus |
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Zika Replication |
- receptors not well characterized - internalize via endocytosis - vesicles fuse with endosome and uncoating takes place - ssRNA genome replicated within spherules made with endoplasmic reticulum - single polyprotein synthesized and inserted in ER membrane - cleaved into individual protein - immature virons assembled in the ER - transit to Golgi where they are processed into mature virions - transit to membrane where they are released - persistent infection |
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Symptoms of Zika |
Same as flu - sever for pregnant women's babies: Microcephaly and gulliain - Barre syndrom GB syndrom- not well understood. Auto immune disease targeting peripheral nerves - weakness, tingling sensation in extremities |
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Zika and Epidemiology |
Zika has been know about for aprox 64-67 years - not known to cause birth defects until current outbreak in Brazil and Central America - unclear why its causing more sever problems now |
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Hypothesis to why Zika became a pandemic |
Evolution of virus make it spred more effectively by vector - evolution of virus to increas viral load in humans thus increasing effective trasmission - Immune system of Brazil and C.America are naive to it so more likely to get it |
