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Viruses What do the following diseases have in common? The common cold Ebola AIDS They are all caused by viruses!!! Now take 1 minute to write down at least 3 things you know about viruses Here is the story of one virus… In 1976 in Zaire (now Congo) several hundred people died horrific deaths in a matter of days from an unknown illness. Symptoms in infected people began 2-21 days after infection and often resulted in massive internal hemorrhaging (bleeding from internal organs). More than half of those who got sick from this disease died. We now know that this disease is… EBOLA What is Ebola? •This is the virus that causes Ebola Hemorrhagic Fever •Ebola is a filamentous virus known as a filovirus •Ebola is transmitted from person-to-person by body fluids http://science.education.nih.gov/home2.nsf/2cacf5795f2bdd8885256ea900678748/ee23d70d186c504c85256ea2006cd6da/$FILE/PHIL_1833low.jpg What does Ebola virus do? Fever Headache Sore throat Diarrhea Coughing blood Vomiting blood Bleeding from eyes Shock and death What does Ebola virus do? Scary things about this disease: 1. Natural reservoir is unknown 2. No standard treatment—only “supportive therapy” Health care workers must be VERY cautious around patients with Ebola 3. Few prevention measures exist 4. 50-90% mortality rate http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/ebola.htm What is a virus? Non-cellular particle Protein http://en.wikipedia.org/wiki/Protein RNA or DNA http://de.wikipedia.org/wiki/DNA made of: And sometimes Lipids http://www.answers.com/topic/lipid-bilayer How big is a virus? Viruses are very small Usually 20400 nanometers in size and cannot be seen with a light microscope About 1000 viruses would fit across the width of a human hair!! Is this larger or smaller than a bacterium???? (smaller) What do viruses do? Viruses Kind of like this! invade cells Then they multiply http://www.history.navy.mil/photos/images/d00001/d02370c.htm How do they know what to do? Viruses contain information (DNA or RNA) that enables them to: 1) Take over the host cell 2) Make more of themselves and 3) Spread to other cells INFORMATION Viruses can’t do this on their own Viruses are dependent on the help of YOUR host cells to reproduce!! Therefore viruses are known as: Obligate Intracellular Parasites So they must live inside cells! In a nutshell… What viruses do is invade cells and reproduce They just happen to kill cells in the process!! Now take 1 minute and sketch what you think a virus looks like…. Over the next few minutes we will see what a few different viruses look like… Structure of a Virus All viruses contain: 1) A shell of protein called a capsid 2) Nucleic acid which stores the information—this can be either DNA or RNA http://www.bioinvision.dk/plantvir2.html Structure of a Virus Some viruses contain an additional outer layer outside the capsid called the envelope Stealth Bomber www.ae.gatech.edu/ ~ptsiotra/airplanes.html The envelope allows the virus to attack its hosts in “stealth mode” because their envelope (outer covering) is usually made from the host cell membrane Structure of an Enveloped Virus Nucleic Acid Capsid Envelope (this virus is in “stealth mode”) http://biodidac.bio.uottawa.ca/thumbnails/filedet.htm?File_name=Viru008b&File_type=gif What do viruses look like? •These are adenoviruses •They do not have envelopes •They are DNA viruses http://www.virology.net/Big_Virology/BVDNAadeno.html What is special about Adenovirus? Adenoviruses use special proteins that stick out from the capsid (called penton fibers) to attach to the host cell. © Copyright Linda M Stannard, 1995. http://web.uct.ac.za/depts/mmi/stannard/emimages.html What is special about Adenovirus? Adenoviruses are among the most common viruses and usually cause mild infections of the respiratory or digestive systems. Typical adenoviruses cause: •Sore throat •Pneumonia •Diarrhea •Pink eye What do viruses look like? This is the virus that causes herpes Herpes is a DNA virus. Capsid Envelope © Copyright Linda M Stannard, 1995. http://web.uct.ac.za/depts/mmi/stannard/emimages.html What’s the deal with Herpes virus? Herpes viruses can cause fever blisters, sexually transmitted genital infections, mononucleosis and even chickenpox. http://www.etsu.edu/cpah/dental/dcte760/apul.htm What do viruses look like? This is Rotavirus The smaller capsid fits inside the larger capsid Rotavirus is interesting because it actually has two capsids instead of just one! © Copyright Linda M Stannard, 1995. http://web.uct.ac.za/depts/mmi/stannard/emimages.html More about Rotavirus •Rotaviruses are RNA viruses. •Rotaviruses are usually transmitted through the fecal-oral route. •Usually cause infections of the digestive system – diarrhea. What do viruses look like? •Influenza Virus – the cause of the flu! •This is an RNA virus © Copyright Linda M Stannard, 1995. http://web.uct.ac.za/depts/mmi/stannard/emimages.html Influenza virus •Influenza virus has an envelope •Influenza killed over 20 million people in 1918-1919. What do viruses look like? •HIV is a retrovirus •HIV has an envelope •HIV is an RNA virus http://research.amnh.org/exhibitions/epidemic/microbes.html What’s the deal with retroviruses? Retroviruses come packaged with a VERY SPECIAL enzyme called reverse transcriptase Reverse transcriptase allows them to make DNA copies of the RNA that they carry with them That DNA can then integrate into the host genome Virus life cycles: What do viruses do all day? Some Virus Review What are viruses made of? – Give two examples of viruses. – Nucleic acid, protein capsid, and sometimes an envelope. Ebola virus, rotavirus, adenovirus, herpes virus, influenza virus, etc. What is unique about a retrovirus? – It carries RNA as its nucleic acid, which it converts into DNA by using the enzyme reverse transcriptase. How do viruses work? The basic steps of the Lytic Cycle 1. The virus must attach to the host cell http://www.cat.cc.md.us/courses/bio141/lecguide/unit2/viruses/u2fig5a.html How do viruses work? The basic steps of the Lytic Cycle 2. The virus injects its nucleic acid (DNA or RNA) into the host cell How do viruses work? The basic steps of the Lytic Cycle 3. The host cell unwittingly makes viral proteins from the viral nucleic acid which: – Destroy the host DNA – Copy the viral nucleic acid – Make more viral capsid proteins How do viruses work? The basic steps of the Lytic Cycle 4. Many new viruses assemble inside the cell How do viruses work? The basic steps of the Lytic Cycle 5. New viruses are released from the cell in two ways: a) Nonenveloped viruses usually cause the host cell to burst The cell is beginning to burst because of all of the emerging viruses http://www.aids-info.ch/e_te/aas-e-imm.htm (Lennert Nilsson, Karolinska Inst., Stockholm) © Boehringer Ingelheim International GmbH How do viruses work? The basic steps of the Lytic Cycle OR… b) Enveloped viruses usually leave the infected cell by budding http://www.aids-info.ch/e_te/aas-e-imm.htm (H.R. Gelderblom, Robert-Koch-Institut, Berlin) Virus budding off the cell membrane How do viruses work? The basic steps of the Lytic Cycle 6. All of the many newly released viruses are free to infect lots of other cells!! How do viruses work? The basic steps of the Lytic Cycle 7. The process then repeats itself over and over again, making us sick. A little bit of review: What does a virus do once it attaches to the host cell? – It injects its nucleic acid into the host cell. What does the viral nucleic acid allow the virus to do? – Destroy the host DNA, replicate the viral nucleic acid, and make more capsids Two Types of Virus Life Cycles: 1.Lytic Cycle—faster, simpler cycle (ex: the flu) • A virus with this cycle makes you sick right away Vs. The Lysogenic Cycle: A Major Variation on the virus life cycle 2. Lysogenic Cycle—slower, more complex cycle (ex: herpes) • This type of virus can “hide out” in the DNA of your cells until it is ready to attack • This type of virus can keep reoccurring… The Lysogenic Virus Cycle Just like in the Lytic Cycle, the lysogenic virus: – Attaches to the host cell – Injects its nucleic acid into the host cell BUT THEN IT DOES SOMETHING DIFFERENT!!!! The Lysogenic Virus Cycle Then the viral DNA integrates into the DNA of the host cell…it becomes part of the host chromosome!!!! When its DNA is inside the host DNA it is called a provirus.(prophage) The Lysogenic Virus Cycle Then every time the host cell reproduces, it copies all of its DNA…including the provirus!!! •So each new host cell will contain the provirus!!! The Lysogenic Virus Cycle Then when conditions are right, the provirus will activate the lytic cycle. The viral DNA makes viral proteins Virus destroys host DNA •Temperature •Stress level •Immune system weakness Virus replicates New viruses burst cell and spread The Lysogenic Virus Cycle lysogenic viruses can “lurk” in host cell DNA, they can be difficult for the body to eradicate As a result, they can stay inside cells as proviruses and can keep causing infections Because The Lysogenic Virus Cycle Example = herpes “cold sores” that keep infecting the mouth may “go away” temporarily, but as long as the provirus lurks in the DNA of your mouth cells, they can enter the lytic cycle to make you miserable Herpes Review Question What makes a lysogenic virus different from a lytic virus? – It can hang out in the host cell DNA as a provirus for many generations of host cell replication! – Every time the host cell reproduces, the “hidden” provirus is also reproduced! How do viruses cause illness and what can be done about it? Think back to the life cycle of a virus… Why do you think the viral life cycle would make us “sick”? Why do viruses make us sick? 1. By destroying our cells when newly assembled viruses are ready to spread to other cells 2. By causing our immune system to respond in a way that gives us symptoms Why do viruses make us sick? 3. By making it easier for other pathogens—such as bacteria—to infect us 4. By promoting cancer in our bodies http://www.niehs.nih.gov/kids/colillness.htm With the person next to you, take 1 minute to devise a way to stop a viral illness. Is There Anything We Can Do to Combat Viral Infections? 1. Washing hands prevents the spread of viruses from person to person 2. Antibodies –your body’s defense against foreign invaders http://www.cryst.bbk.ac.uk/PPS2/course/section10/mosaic.html Is There Anything We Can Do to Combat Viral Infections? 3. Antiviral drugs—these drugs can prevent: viral penetration nucleic acid synthesis viral assembly viral release Is There Anything We Can Do to Combat Viral Infections? 4. Interferons – natural proteins made by the body: usually produced in response to one infection make cells resistant to infection by other viruses http://www.gpnotebook.co.uk/cache/-1643773914.htm We can “help” our immune system to produce antibodies by using vaccines Important vocabulary in understanding vaccines: 1) Immune response: your body’s defenses that attack a disease-causing agent (pathogen) 2) Antigen: a substance (such as a virus or bacterium) that triggers an immune response When you receive a vaccine you are injected with either: “inactivated” or “killed” pathogen An antigenic part of the pathogen (such as part of the cell wall or flagellum) A living but weakened version of the pathogen – This is the most effective type of vaccine, but why might it not be advisable for patients with weakened immune systems??? An How is the most common flu vaccine made? How is the most common flu vaccine made? In February, the scientists at the World Health Organization predict which versions of the flu virus are going to affect the Northern Hemisphere They usually choose three strains of the virus In the best years, their prediction is only 75% effective How is the most common flu vaccine made? The live virus strains are injected into chicken eggs The virus replicates inside the eggs The virus is then extracted and purified from the eggs and killed with a chemical such as formaldehyde Then the dead virus can be injected into people as the “flu shot” http://www.bbc.co.uk/gcsebitesize Once you receive the vaccination… Your immune system responds in two ways: 1) Some of the cells of your immune system produce antibodies that bind to the disease-causing organism…eventually leading to its death. 2) Memory cells are formed that “remember” what the antigen looked like These memory cells are key… Because the next time you get the disease, these memory cells recognize the antigen and produce antibodies VERY QUICKLY The quicker your immune system responds, the less sick you get… http://www.bbc.co.uk/gcsebitesize So in a nutshell… A vaccine exposes your immune system to a form of the disease Preventing you from getting sick Causing it to “remember” that antigen So that the next time you get the disease, your immune system can act quickly Important viral diseases with vaccines •Chickenpox •Influenza •Smallpox •Polio •Measles •Hepatitis A •Mumps •Hepatitis B •Rubella We currently DO NOT have vaccines for HIV or the common cold