Transcript Viruses
Viruses The word Virus comes from the Latin word meaning “poison”. Tobacco mosaic virus stunts the growth of tobacco plants and gives their leaves a mottled, mosaic coloration. Studied as early as 1883 by Adolf Mayer, but basically could not be grown in a lab, could not be filtered or seen with a microscope. Was not isolated and identified until 1935 by an American scientist Wendell Stanley. A virus consists of either DNA or RNA enclosed in a protein shell or coat called a capsid. Some viruses are also covered by a membranous envelope that is derived from the membrane of the host cell. ( Influenza has this, it is called enveloped) Sooooooo small, that they are seen only with an electron microscope A virus is an intracellular parasite that can reproduce only by taking over a host cell’s equipment. They do not feed, grow, reproduce, take in or release energy outside of the host cell. They have no cell parts: no cytoplasm, no organelles, no cell membrane. They may attack plants, animals, bacteria, protists. Viral Diseases • • • • • • • • • • • • Cold Flu Polio Measles Herpes virus: Chicken pox (herpes zoster), shingles, cold sores, infectious mononucleosis, genital herpes Mumps Rabies (attacks CNS of warm blooded animals… foxes, skunks, bats, raccoons) HIV SARS (coronavirus…upper respiratory infections) Hepatitis (liver damage) Ebola, Marburg ( hemorrhagic) Papillomavirus (warts) Ebola Herpes zoster Bird Flu Cold virus polio Bacteriophage Bacteriophage or Phage Virus: attack bacterial cells Contractile sheath Tail Tail fibers Lytic Cycle Lytic and Lysogenic cycle Naming flu viruses • Influenza viruses are defined by two protein components, known as antigens on the surface of the virus • Haemagglutinin (H) and Neuraminidase (N) • Influenza viruses that cause human disease are divided into two groups: A and B • Influenza A has two subtypes that are important for humans A(H3N2) and A(H1N1). • The numbers refer to slight variations • Avian Flu (H5N1) • Large-scale outbreaks are called epidemics. If they spread worldwide, they're called pandemics. Flu Vaccines • Flu vaccines must be reformulated from scratch every year to keep pace with the mutations of influenza viruses. • The process is a long one, lasting close to a year • In Canada the flu season runs from November to April. • Beginning in February the WHO studies the new strain mutations for next winter’s vaccination. • 83 countries provide information to the WHO and a vaccine is created that targets the three most virulent strains in circulation • The vaccines are developed using fertilized chick eggs • The shell of a 10-day old is cracked and the flu virus injected into the fluid surrounding the embryo • The egg is resealed allowing the embryo to become infected • The virus is harvest two days later • A single egg is required to make one dose of a vaccine strain, requiring the use of 10’s x millions of eggs every year • Flu vaccines are available as a shot or nasal mist. • The shot contains killed flu viruses that won't cause you to get the flu, but will make your body create antibodies that fight off infection if you encounter the live flu virus. • The nasal mist contains weakened live flu viruses. Because it contains live viruses, the mist is not for people with weakened immune systems or certain health conditions. It is only for healthy, non-pregnant, people between the ages of 2 and 49 years.