326Mvirology - INTRODUCTION TO VIROLOGY Viruses are...

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INTRODUCTION TO VIROLOGY Viruses are obligate intracellular parasites; (virions) not truly living Have no means to produce energy; only a few enzymes; no ribosomes (unlike bacteria) are pathogens for animals, plants, fungi, bacteria (bacteriophage) The nucleocapsid is a protein shell (capsid) surrounding RNA or DNA core (either/or, NOT both unlike bacteria) Capsids have many different shapes (symmetrical) human viruses with “helical” symmetry usually have RNA genome Many viral nucleocapsids are surrounded by membranous envelope that contain viral specific proteins and host membrane components Budding viruses “bud” thru the cell’s membrane(s) after they have inserted viral proteins into them; these viruses then become enveloped (e.g. influena virus) Lytic viruses rupture the cell and are then released; are usually not enveloped (e.g. poliovirus)
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INFLUENZA VIRUS- A RESPIRATORY VIRUS Influenza and influenza-like illnesses- ancient; "the influence" Incorrectly attributed to Haemophilus influenzae , b/c this Gram negative rod (a secondary invader) was isolated from throats of people with viral influenza Viral etiology discovered 1933 Since 1173, >300 epidemics reported (about every 2.4 yrs.); 22 pandemics reported since early 18th century Right after WWI- Spanish influenza pandemic killed 20 million! Pandemics this century 1918, 1957, 1968; GREAT concern about another pandemic occurring (possibly from the “new” Avian to human strain Transmission and entry of virus Transmitted to nasopharynx of susceptible individuals by aerosols (sneezes, coughs) Children are often virus "aerosol bombs" Infects upper and lower respiratory tract epithelia Cells damaged and destroyed after intial viral multiplication releasing viral Ag and destructive cellular material; M Φ , lymphocytes, inflammatory mediators (IL-1, interferon α , β29 These mediators cause fever, myalgia, and vasodilation, edema in the URT- stuffiness (congestion) and running noses in LRT- mucus production-coughing if respiratory epithelia has been severely damaged,
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superinfecting bacteria can cause secondary severe disease (bronchitis or pneumonia with Haemophilus , staph, pneumococci) in children, otitis media- common secondary disease; also in children receiving salicylates (aspirin) an often fatal encephalopathy, Reyes Syndrome, can occur Influenza virus is a budding, enveloped virus Belongs to Orthomyxovirus group Two major types A and B; A is the one that causes greatest concern Envelope is covered with spikes (“peplomers”) of hemagglutinin (HA), neuraminidase (NA) Influenza virus infection of host cell Binding of HA to cell surface glycoproteins and glycolipids Viruses are engulfed in phagosomes; acidic environment causes virus envelope to fuse with endosome's membrane- uncoating virus (removing envelope) and releasing it into cytoplasm Nucleocapsid transported to nucleus, replication
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326Mvirology - INTRODUCTION TO VIROLOGY Viruses are...

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