Viruses  What is a virus?  What is their composition and structure?  What are the major viruses and how are they transmitted? What are their symptoms?  How do they reproduce?

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

What is a Virus?  A virus is not strictly alive.. nor is it strictly dead...  A virus has some fundamental information (genes made of DNA or RNA) which allows it to make copies of itself.  However, the virus must be inside a living cell of some kind before the information can be used. A HOST!  In fact, the information won't be made available unless the virus enters a living cell. It is this entrance of a virus into a cell which is called a viral infection.  A virus is.02 to.25 microns in diameter. (smallest bacteria is.4) Smaller than Ribosomes

Where do Viruses Come From? Three Possible Theories! 1. If they are not cells and require living cells for replication, than viruses must not have been present prior to cellular evolution and could therefore have coevolved with cells. 2.Were once cells but have lost all cellular functions retaining only information to replicate themselves using hosts machinery 2.Were once cells but have lost all cellular functions retaining only information to replicate themselves using hosts machinery 3.Viruses have evolved from plasmids (plasmids are self replicating independent DNA) or from RNA viroids. These "early" viruses did not contain genes for capsids. As viroids moved from cell to another, it picked up such genes

HIV Virus

The Life Cycle of a Virus The Lytic Cycle!  Penetration  When a virus infects a cell, it first binds with the cell membrane using receptor molecules on the virus's surface. The virus then injects its genetic material, which can be either DNA or RNA, into the cell's nucleus.  Biosynthesis  The viral nucleic acid takes over and uses the host cell’s organelles to make many copies of the virus. In the case of DNA viruses, the DNA transcribes itself into messenger RNA (mRNA) molecules that are then used to direct the ribosome. In retroviruses, or RNA viruses, a unique enzyme called reverse transcriptase transcribes the viral RNA into DNA, which is then transcribed again into mRNA. However, a different type of retrovirus replicates using RNA Polymerase to fashion RNA directly from the virus's own RNA.  Maturation and lysis  After many virus copies are made, they are assembled into complete viruses. The cell eventually becomes filled with viruses (typically ) until it bursts, or lysis; this end process gives the cycle its name. The new viruses are free to infect other cells.

Infection cycle of H5N1 Avian Influenza

HIV cycle

HIV particle

Virus Pictures Ebola Virus

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

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

Other Viruses  HIV and Aids 1. Transmission by contact with blood or body fluids of infected person 2. Symptoms Immune system failure What are white and red blood cells? What are white and red blood cells?  Influenza 1. Transmission by airborne droplets 2.Respiratory system problems

Virus Pictures HIV

Virus Pictures