Viruses

Egyptian stele (1580-1350 B.C) Crippled priest Egyptian stele dating from the 18th Dynasty (1580-1350 BC). A crippled young man, apparently a priest, is pictured with a withered and shortened left leg, with his foot in the typical equinus position characteristic of flaccid paralysis; his staff is apparently being used as a support. Carlsberg Glyphotheke, Copenhagen.

Poxviruses (Poxviridae) The Pharaoh Ramses V died of smallpox (variola virus) in 1157 B.C. In 1520: 22 - 3.5 million Aztecs died Last case in Somalia on 26th October 1977 Sept.11—variola virus as a bioterrorism weapon? Don’t confuse with chickenpox (varicella)

VIRUSES Virus = Latin for poison Isolation of the first Virus Dmitri Iwanowski in 1892 Tobacco mosaic virus which affects >150 plants world wide stunted growth “filterable agent”                                2

VIRUSES, LIVING ORGANISMS? Life=A complex set of processes resulting from the actions of proteins specified by nucleic acids Viruses: Inert outside host cells Obligate intracellular parasites Do not divide 3

VIRION A complete, fully developed viral particle Virions are the transmissible state of a virus. Metabolically inert Virions must be able to adhere and allow entry into some host cell(s) Also to survive outside of host cell environment. Some virions more hardy than others (hepatitis virus A can withstand short periods of boiling; most virions are destroyed by this) 4

VIRUS SIZE Most, 20 to 300 nm (0.02 to 0.3 mm) Filoviruses up to 14,000 nm Exceptional 13

Only one type of nucleic acid (NA) DNA or RNA STRUCTURE OF VIRUSES Only one type of nucleic acid (NA) DNA or RNA NA enclosed by a protein coat 5

Types of viral nucleic acids Circular Linear Segmented

Protein subunits, building blocks of the viral capsid VIRAL CAPSOMERS Protein subunits, building blocks of the viral capsid 15

Capsid composed of repeating subunits - capsomers STRUCTURE OF VIRUSES Capsid composed of repeating subunits - capsomers helical, icosahedral, complex protection, attachment, 8

Part of host’s cell membrane ENVELOPED VIRUSES Envelope present Part of host’s cell membrane 9

Structure of Viruses Envelope derived from host membrane lipids and virus proteins nuclear, plasma membrane by budding necessary for attachment

Nucleic acid Capsid Envelope

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NONENVELOPED OR NAKED VIRUSES Envelope absent More resistant than enveloped viruses 10

"Naked" viruses require host death so viruses can be released Enveloped viruses: are shed virus particles ; they shed by budding out, continued release from cell membrane Cell does not die (immediately), continues to serve as factory for virus assembly and release. Virus typically acquires a coating of host cell membrane, and will include virus-specific proteins. This is the "envelope"

Examples of enveloped viruses include: Retrovirus, I.e. HIV Paramyxovirus, I.e. influenza Rhabdovirus, I.e. rabies Enveloped Herpes virus

Naked virus (no envelope) Nucleic acid Capsid

Bacteriophages (Virus that infects Bacteria) TYPES OF VIRUSES Animal viruses Plant viruses Bacteriophages (Virus that infects Bacteria) Ex: Coliphage infect E.coli cells 7

Types of Viral Infections Oncogenic viruses Herpes viruses

Multiply using the machinery of the host cell Have few or no enzymes VIRAL METABOLISM Multiply using the machinery of the host cell Have few or no enzymes 11

HOST RANGE Species specific Small pox virus, humans Broad host range Rabies virus, mammals 12

VIRAL SPIKES Carbohydrate/protein complexes embedded in the viral envelope Used as means of identification Influenza virus, avian flue (H5N1)/Adenovirus 16

Adenovirus spikes Respiratory Illness, Common Cold, “Pink Eye”, Gastrointestinal Illness

Cylindrical capsid with a helical structure Polyhedral VIRAL MORPHOLOGY Helical Cylindrical capsid with a helical structure Polyhedral Icosahedral (20 triangular faces and 12 corners) 17

Helical nucleocapsid

RHABDOVIRUS 20

POLYHEDRAL

VIRAL MORPHOLOGY (cont.) Complex viruses Structures attached to capsid Tail, tail fibers Bacteriophages 22

Tail Bacteriophage 23

POXVIRUS Infections due to the poxviruses (members of the Poxviridae family) occur in humans and animals. The orthopoxviruses include smallpox (variola), monkeypox, vaccinia, and cowpox viruses. 29

CLASSIFICATION OF ANIMAL VIRUSES Type of nucleic acid DNA or RNA Single stranded (ss) or double stranded (ds) Presence of envelope 25

CLASSIFICATION OF ANIMAL VIRUSES Strategy for Replication Where do they replicate? Morphology Structures Described by common Names Where is their niche? (Enteroviruses)

Classification of viruses

CLASSIFICATION OF ANIMAL VIRUSES (cont.) ssDNA, nonenveloped Parvovirus (Parvovirus B19 Fetal Death, GI) dsDNA, nonenveloped Adenovirus (Respiratory, GI) Papovavirus (Warts, Tumors) 27

CLASSIFICATION OF ANIMAL VIRUSES (cont.) dsDNA, enveloped Poxvirus (Smallpox, Cowpox) Herpesvirus (Fever blisters, Chicken pox, Shingles, Mononucleosis) Hepadnavirus (Hepatitis B, Tumors) 28

HERPESVIRUS 30

CLASSIFICATION OF ANIMAL VIRUSES (cont.) ssRNA, nonenveloped Picornavirus (Polio, Common Cold, GI) dsRNA nonenveloped Reovirus (GI, Respiratory) dsRNA enveloped Retrovirus (Tumors, AIDS) 31

POLIOVIRUS 32

Polivirus structure 33

REOVIRUS Reoviruses are infectious agents of the virus family Reoviridae, transmitted by respiratory and fecal-oral routes. They are not major human pathogens reo (for respiratory, enteric, and orphan, the latter meaning not associated with human disease) 34

RETROVIRUS They are enveloped viruses, with an RNA genome. The name is derived from the fact that the virus particle contains an RNA-dependent DNA Polymerase (Reverse transcriptase) This enzyme converts the RNA genome into DNA, which then integrates into the host chromosomal DNA. The reverse transcriptase is highly error prone and rapid genetic variation is a feature of this group 35

CLASSIFICATION OF ANIMAL VIRUSES (cont.) ssRNA, enveloped Togavirus (Encephalitis) Flavivirus (Dengue Fever, Yellow Fever, West Nile Virus) Coronavirus (Common Cold) Rhabdovirus (Rabies) 36

CORONAVIRUS 37

CLASSIFICATION OF ANIMAL VIRUSES (cont.) ssRNA, enveloped Filovirus (Ebola, Marburg) Arenavirus (Hemorrhagic Fever) Paramyxovirus (Mumps) Orthomyxovirus (Influenza) Bunyavirus (Hantavirus) 38

FILOVIRUS Marburg and Ebola virus Filo = threadlike Appear in many different shapes (pleomorphic) First ID in Germany/Yugoslavia from tissues of green monkeys who developed hemorrhagic fever Filo = threadlike Filovirus. Although very "hot" in the news, these viruses are very poorly characterized because of their extreme pathogenicity. They are class IV pathogens, meaning they can only be cultured in total containment facilities, of which there are only two in the U. S. They are thought to be enveloped viruses with - RNA genomes. 39

PART II

GROWTH OF VIRUSES Bacteriophages Bacterial cells Animal viruses Animal cells Animals and embryos 40

Growing Viruses Animal Viruses A. Living Animals mice, rabbits, guinea pigs B. Chicken Embryos (Eggs) used to be most common method to grow viruses Still used to produce many vaccines (Flu Vaccine) C. Cell Cultures Most common method to grow viruses today

PLAQUE ASSAY 52

LIVING ANIMALS Diagnostic Vaccine research Expensive Regulated 41

NEWBORN MOUSE 42

EMBRYONATED EGGS Diagnostic Vaccine production Inexpensive Unregulated 43

CHIKEN EMBRYO 44

CHIKEN EMBRYO 45

CHICKEN EMBRYO 46

Derived from animals, or humans Culture in special medium ANIMAL CELL CULTURES Derived from animals, or humans Culture in special medium Infected cells show cytopathic effect (CPE) 48

Infected monkey cells Non-infected monkey cells 49

Multinucleated (giant) cells infected with reovirus 50

INCLUSION BODIES POX VIRUS 51

ANIMAL CELL CULTURES Primary cell lines Tissues Diploid cell lines Human embryos Continuous cell lines Cancerous cells 53

dedicated to the memory of Mrs. Henrietta Lacks, whose very cells, “...This lecture is dedicated to the memory of Mrs. Henrietta Lacks, whose very cells, after her death, have helped scientist all around the world to find ways to alleviate suffering and prevent disease among all of us, who are still here...”

VIRAL IDENTIFICATION METHODS Electron microscopy Serological Specific antibodies Molecular biology Nucleic acid sequences 54

VIRAL MULTIPLICATION Viral genes Viral proteins A few enzymes (if any) usually involved with viral nucleic acid replication 56

VIRAL MULTIPLICATION (cont.) Infected cell provides: Enzymes and machinery for viral nucleic acid and protein synthesis Energy 57

BACTERIOPHAGE MULTIPLICATION Lytic cycle (lytic phages) Lysis and death of host cell Lysogenic cycle (Lysogenic or temperate phages) Host cell carries phage NA and divides normally 58

LYSOGENIC (TEMPERATE) PHAGES Upon infection phage inserts its DNA into the host chromosome (prophage) Prophage genes may alter host cell characteristics by transduction 59

Phage picks up, randomly, fragments of host DNA instead of phage’s DNA TRANSDUCTION Generalized Phage picks up, randomly, fragments of host DNA instead of phage’s DNA May transfer any gene 60

TRANSDUCTION (cont.) Specialized Phage DNA that has been integrated to host DNA is exised along with a few adjacent host genes 61

LYSOGENIC PHAGES (cont.) Toxins produced by: Corynebacterium diphteriae Streptococcus pyogenes Clostridium botulinum 62

VIRAL MULTIPLICATION Attachment Penetration Biosynthesis Maturation Release 63

Viral nucleic acid gets integrated into host genome ONCOGENIC VIRUSES Viral nucleic acid gets integrated into host genome Alteration of cellular growth genes 70

LATENT VIRAL INFECTIONS Virus/host equilibrium Herpes viruses Cold sores Shingles (chicken pox) 71

Virus builds up gradually Usually fatal SLOW VIRAL INFECTIONS Virus builds up gradually Usually fatal Subacute sclerosing panencephalitis 72

Undetectable nucleic acid?, a bacterium? Neurological diseases PRIONS Protein Undetectable nucleic acid?, a bacterium? Neurological diseases Creutzfeldt-Jacob disease Mad cow disease 73

HOST CELL DEFENSES

Antiviral proteins (AVP) produced by virus-infected cells INTERFERON (IFN) Antiviral proteins (AVP) produced by virus-infected cells Interfere with viral multiplication 74

No effect on infected cells INTERFERON (cont.) Host-cell specific Not virus specific Short lived No effect on infected cells 75

INTERFERON TYPES Alpha (a-IFN) Beta (b-IFN) Gamma (g-IFN) 76

IFNs diffuse and gain entrance to non-infected neighboring cells INTERFERON ACTIVITY IFNs diffuse and gain entrance to non-infected neighboring cells Induce synthesis of antiviral proteins 77

Destruction of viral mRNA Inhibit translation of viral mRNA INTERFERON ACTIVITY Antiviral proteins: Destruction of viral mRNA Inhibit translation of viral mRNA Inhibit polypeptide elongation 78

RABBITS AND MYXOMATOSIS 79

Introduced Rabbits First arrived in 1778 from Europe AUSTRALIA Introduced Rabbits First arrived in 1778 from Europe Spread 125 Km/year Soon became a pest 80

Mild infection in Australian native rabbits MYXOMATOSIS Caused by a poxvirus Mild infection in Australian native rabbits Fatal infection in the introduced European rabbits 81

TRANSMISSION OF MYXOMATOSIS Mosquito Flea Direct contact 82

MYXOMA VIRUS IN AUSTRALIA Introduced in the Summer 1950-1951 By 1956 the European rabbit population dropped 90% 83

MYXOMA VIRUS IN AUSTRALIA (cont.) As time went on: Rabbit population began to recover Appearance of less virulent viruses Appearance of more resistant rabbits 84