VirusesViruses

What is a virus?What is a virus? What is their composition and structure?What is their composition and structure? What are the major viruses and how are What are the major viruses and how are

they transmitted? What are their they transmitted? What are their symptoms?symptoms?

How do they reproduce?How do they reproduce?

Virus InformationVirus Information IntroductionIntroduction

First, let me tell you what a virus is NOT. First, let me tell you what a virus is NOT. A A virus is not a bacteriumvirus is not a bacterium, nor , nor an an independently-living organismindependently-living organism. . A virus A virus cannotcannot survive without a living cellsurvive without a living cell within which within which toto synthesize copies of itself (synthesize copies of itself (replicatereplicate). ). Viruses Viruses need A host to surviveneed A host to survive). Antibiotics do not ). Antibiotics do not harm a virus; it is for this reason that harm a virus; it is for this reason that treatment for the "flu" for example, is mainly treatment for the "flu" for example, is mainly to help ease the symptoms of the illness to help ease the symptoms of the illness rather than to kill the organism which causes rather than to kill the organism which causes the "flu" (the "flu" (Influenza virus)Influenza virus)

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What is a Virus? What is a Virus? A virus is not strictly alive.. nor is it strictly dead... A virus is not strictly alive.. nor is it strictly dead... A virus has some fundamental information (genes A virus has some fundamental information (genes

made of DNA or RNAmade of DNA or RNA) which allows it to make copies ) which allows it to make copies of itself. of itself.

However, the virus must be However, the virus must be insideinside a living cell of some a living cell of some kind before the information can be used. A HOSTkind before the information can be used. A HOST!!

In fact, the information won't be made available unless In fact, the information won't be made available unless the virus enters a living cell. It is this entrance of a the virus enters a living cell. It is this entrance of a virus into a cell which is called a viral infection. virus into a cell which is called a viral infection.

A virus is A virus is .02 to .25 microns.02 to .25 microns in diameter. (smallest in diameter. (smallest bacteria is .4) Smaller than bacteria is .4) Smaller than RibosomesRibosomes

Where do Viruses Come Where do Viruses Come From?From?Three Possible Theories!Three Possible Theories!

1.1. If they are not cells and require living cells for If they are not cells and require living cells for replication, than viruses must not have been replication, than viruses must not have been present prior to cellular evolution and could present prior to cellular evolution and could therefore have therefore have coevolved with cellscoevolved with cells..

2.2.Were once cells but have lost all cellular functionsWere once cells but have lost all cellular functions retaining only information to replicate themselves retaining only information to replicate themselves using hostsusing hosts machinery machinery

3.Viruses have evolved from plasmids3.Viruses have evolved from plasmids (plasmids are (plasmids are self replicating independent DNA) or from RNA self replicating independent DNA) or from RNA viroids. These "early" viruses did not contain viroids. These "early" viruses did not contain genes for capsids. As viroids moved from cell to genes for capsids. As viroids moved from cell to another, it picked up such genesanother, it picked up such genes

HIV VirusHIV Virus

The Life Cycle of a VirusThe Life Cycle of a VirusThe Lytic Cycle! The Lytic Cycle! PenetrationPenetration When a virus infects a cell, it first When a virus infects a cell, it first binds with the cell membranebinds with the cell membrane using using

receptor molecules on the virus's surface. The virus then receptor molecules on the virus's surface. The virus then injects its genetic injects its genetic materialmaterial, which can be either , which can be either DNA or RNA, into the cell's nucleusDNA or RNA, into the cell's nucleus..

BiosynthesisBiosynthesis The viral nucleic acid takes over and The viral nucleic acid takes over and uses the host cell’s organelles to make uses the host cell’s organelles to make

many copies of the virusmany copies of the virus. In the case of DNA viruses, the DNA transcribes . In the case of DNA viruses, the DNA transcribes itself into messenger RNA (mRNA) molecules that are then used to direct itself into messenger RNA (mRNA) molecules that are then used to direct the ribosome. In retroviruses, or RNA viruses, a unique enzyme called the ribosome. In retroviruses, or RNA viruses, a unique enzyme called reverse transcriptase transcribes the viral RNA into DNA, which is then reverse transcriptase transcribes the viral RNA into DNA, which is then transcribed again into mRNA. However, a different type of retrovirus transcribed again into mRNA. However, a different type of retrovirus replicates using RNA Polymerase to fashion RNA directly from the virus's replicates using RNA Polymerase to fashion RNA directly from the virus's own RNA.own RNA.

Maturation and lysisMaturation and lysis After many virus copies are made, they are assembled into complete After many virus copies are made, they are assembled into complete

viruses. The viruses. The cell eventually becomes filled with virusescell eventually becomes filled with viruses (typically 100-200) (typically 100-200) until it bursts, or lysisuntil it bursts, or lysis; this end process gives the cycle its name. ; this end process gives the cycle its name. The new The new viruses are free to infect other cells.viruses are free to infect other cells.

Infection cycle of H5N1 Avian Influenza

HIV cycleHIV cycle

HIV particle

Virus PicturesVirus Pictures

Ebola Virus

Transmission of EbolaTransmission of Ebola

Infections with Ebola virus are acute. There is no Infections with Ebola virus are acute. There is no carrier state. Because the natural reservoir of the virus carrier state. Because the natural reservoir of the virus is unknown, the manner in which the virus first appears is unknown, the manner in which the virus first appears in a human at the start of an outbreak has not been in a human at the start of an outbreak has not been determined. However, researchers have hypothesized determined. However, researchers have hypothesized that the first patient becomes infected through contact that the first patient becomes infected through contact with an infected animal.   After the first case-patient in with an infected animal.   After the first case-patient in an outbreak setting is infected, the virus can be an outbreak setting is infected, the virus can be transmitted in several ways. People can be exposed to transmitted in several ways. People can be exposed to Ebola virus from direct contact with the blood and/or Ebola virus from direct contact with the blood and/or secretions of an infected person.secretions of an infected person.

Symptoms of EbolaSymptoms of Ebola

The incubation period for Ebola HF The incubation period for Ebola HF ranges from 2 to 21 days. The onset of ranges from 2 to 21 days. The onset of illness is abrupt and is characterized by illness is abrupt and is characterized by fever, headache, joint and muscle aches, fever, headache, joint and muscle aches, sore throat, and weakness, followed by sore throat, and weakness, followed by diarrhea, vomiting, and stomach pain. A diarrhea, vomiting, and stomach pain. A rash, red eyes, hiccups and internal and rash, red eyes, hiccups and internal and external bleeding may be seen in some external bleeding may be seen in some patients. patients.

Other VirusesOther Viruses

HIV and Aids HIV and Aids 1. Transmission by contact with blood or body 1. Transmission by contact with blood or body

fluids of infected personfluids of infected person2.2. Symptoms Immune system failureSymptoms Immune system failure What are white and red blood cells? What are white and red blood cells?

Influenza Influenza 1. Transmission by airborne droplets1. Transmission by airborne droplets2.2. Respiratory system problemsRespiratory system problems

Virus PicturesVirus Pictures

HIV

Virus PicturesVirus Pictures

Virus PicturesVirus Pictures

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