viruses
DESCRIPTION
Viruses. Egyptian stele (1580-1350 B.C) Crippled priest. 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? - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/1.jpg)
Viruses
![Page 2: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/2.jpg)
Egyptian stele(1580-1350 B.C)Crippled priest
![Page 3: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/3.jpg)
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)
![Page 4: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/4.jpg)
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”
![Page 5: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/5.jpg)
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
![Page 6: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/6.jpg)
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)
![Page 7: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/7.jpg)
VIRUS SIZE• Most, 20 to 300 nm
–(0.02 to 0.3 m)• Filoviruses up to 14,000 nm
–Exceptional
![Page 8: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/8.jpg)
![Page 9: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/9.jpg)
STRUCTURE OF VIRUSES• Only one type of nucleic acid
(NA)–DNA or RNA
• NA enclosed by a protein coat
![Page 10: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/10.jpg)
Circular Linear
Segmented
Types of viral nucleic acids
![Page 11: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/11.jpg)
VIRAL CAPSOMERS• Protein
subunits, building blocks of the viral capsid
![Page 12: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/12.jpg)
STRUCTURE OF VIRUSES
• Capsid composed of repeating subunits - capsomers
• helical, icosahedral, complex • protection, attachment,
![Page 13: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/13.jpg)
ENVELOPED VIRUSES• Envelope present
–Part of host’s cell membrane
![Page 14: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/14.jpg)
Structure of Viruses
•Envelope derived from host membrane lipids and virus proteins •nuclear, plasma membrane by budding •necessary for attachment
![Page 15: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/15.jpg)
Capsid
Envelope
Nucleicacid
![Page 16: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/16.jpg)
![Page 17: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/17.jpg)
![Page 18: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/18.jpg)
NONENVELOPED OR NAKED VIRUSES
• Envelope absent• More resistant than enveloped viruses
![Page 19: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/19.jpg)
• "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"
![Page 20: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/20.jpg)
Examples of enveloped viruses include:
•Retrovirus, I.e. HIV
•Paramyxovirus, I.e. influenza
•Rhabdovirus, I.e. rabies
•Enveloped Herpes virus
![Page 21: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/21.jpg)
Nucleic acid
Capsid
Naked virus (no envelope)
![Page 22: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/22.jpg)
TYPES OF VIRUSES• Animal viruses• Plant viruses• Bacteriophages (Virus that
infects Bacteria)–Ex: Coliphage infect E.coli cells
![Page 23: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/23.jpg)
Types of Viral Infections
Oncogenic viruses
Herpes viruses
![Page 24: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/24.jpg)
VIRAL METABOLISM• Multiply using the machinery
of the host cell• Have few or no enzymes
![Page 25: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/25.jpg)
HOST RANGE• Species specific
–Small pox virus, humans• Broad host range
–Rabies virus, mammals
![Page 26: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/26.jpg)
VIRAL SPIKES• Carbohydrate/protein complexes
embedded in the viral envelope• Used as means of identification
–Influenza virus, avian flue (H5N1)/Adenovirus
![Page 27: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/27.jpg)
Adenovirus spikesRespiratory Illness, Common Cold,
“Pink Eye”, Gastrointestinal Illness
![Page 28: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/28.jpg)
VIRAL MORPHOLOGY• Helical
–Cylindrical capsid with a helical structure
• Polyhedral–Icosahedral (20 triangular faces and 12 corners)
![Page 29: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/29.jpg)
Helical nucleocapsid
![Page 30: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/30.jpg)
RHABDOVIRUS
![Page 31: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/31.jpg)
POLYHEDRAL
![Page 32: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/32.jpg)
VIRAL MORPHOLOGY (cont.)
• Complex viruses–Structures attached to capsid
•Tail, tail fibers–Bacteriophages
![Page 33: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/33.jpg)
Bacteriophage
Tail
![Page 34: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/34.jpg)
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.
![Page 35: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/35.jpg)
CLASSIFICATION OF ANIMAL VIRUSES
• Type of nucleic acid–DNA or RNA–Single stranded (ss) or double stranded (ds)
• Presence of envelope
![Page 36: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/36.jpg)
CLASSIFICATION OF ANIMAL VIRUSES
• Strategy for Replication–Where do they replicate?
• Morphology–Structures–Described by common Names–Where is their niche?
(Enteroviruses)
![Page 37: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/37.jpg)
Non-enveloped EnvelopeddsDNA Adenovirus
PapovavirusHerpesvirusPoxvirusHepadenavirus
ssDNA Parvovirus -dsRNA Reovirus RetrovirusssRNA Picornavirus Togavirus
FlavivirusCoronavirusRhabdovirus
Classification of viruses
![Page 38: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/38.jpg)
CLASSIFICATION OF ANIMAL VIRUSES (cont.)
• ssDNA, nonenveloped–Parvovirus (Parvovirus B19 Fetal
Death, GI)• dsDNA, nonenveloped
–Adenovirus (Respiratory, GI)
–Papovavirus (Warts, Tumors)
![Page 39: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/39.jpg)
CLASSIFICATION OF ANIMAL VIRUSES (cont.)
• dsDNA, enveloped–Poxvirus (Smallpox, Cowpox)
–Herpesvirus (Fever blisters, Chicken pox, Shingles, Mononucleosis)
–Hepadnavirus (Hepatitis B, Tumors)
![Page 40: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/40.jpg)
HERPESVIRUS
![Page 41: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/41.jpg)
CLASSIFICATION OF ANIMAL VIRUSES (cont.)
• ssRNA, nonenveloped–Picornavirus (Polio, Common Cold,
GI)• dsRNA nonenveloped
–Reovirus (GI, Respiratory)• dsRNA enveloped
–Retrovirus (Tumors, AIDS)
![Page 42: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/42.jpg)
POLIOVIRUS
![Page 43: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/43.jpg)
Polivirus structure
![Page 44: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/44.jpg)
REOVIRUS
reo (for respiratory, enteric, and orphan, the latter meaning not associated with human disease)
Reoviruses are infectious agents of the virus family Reoviridae, transmitted by respiratory and fecal-oral routes. They are not major human pathogens
![Page 45: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/45.jpg)
RETROVIRUSThey 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
![Page 46: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/46.jpg)
CLASSIFICATION OF ANIMAL VIRUSES (cont.)
• ssRNA, enveloped–Togavirus (Encephalitis) –Flavivirus (Dengue Fever,
Yellow Fever, West Nile Virus)
–Coronavirus (Common Cold)
–Rhabdovirus (Rabies)
![Page 47: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/47.jpg)
CORONAVIRUS
![Page 48: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/48.jpg)
CLASSIFICATION OF ANIMAL VIRUSES (cont.)
• ssRNA, enveloped–Filovirus (Ebola, Marburg) –Arenavirus (Hemorrhagic Fever)
–Paramyxovirus (Mumps)
–Orthomyxovirus (Influenza)
–Bunyavirus (Hantavirus)
![Page 49: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/49.jpg)
FILOVIRUS
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.
Marburg and Ebola virus
Appear in many different shapes (pleomorphic)
First ID in Germany/Yugoslavia from tissues of green monkeys who developed hemorrhagic fever
Filo = threadlike
![Page 50: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/50.jpg)
PART II
![Page 51: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/51.jpg)
GROWTH OF VIRUSES• Bacteriophages
–Bacterial cells• Animal viruses
–Animal cells–Animals and embryos
![Page 52: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/52.jpg)
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
![Page 53: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/53.jpg)
PLAQUE ASSAY
![Page 54: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/54.jpg)
LIVING ANIMALS• Diagnostic• Vaccine research• Expensive• Regulated
![Page 55: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/55.jpg)
NEWBORN MOUSE
![Page 56: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/56.jpg)
EMBRYONATED EGGS• Diagnostic• Vaccine production• Inexpensive• Unregulated
![Page 57: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/57.jpg)
CHIKEN EMBRYO
![Page 58: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/58.jpg)
CHIKEN EMBRYO
![Page 59: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/59.jpg)
CHICKEN EMBRYO
![Page 60: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/60.jpg)
ANIMAL CELL CULTURES• Derived from animals, or
humans• Culture in special medium• Infected cells show
cytopathic effect (CPE)
![Page 61: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/61.jpg)
Non-infectedmonkey cells
Infectedmonkey cells
![Page 62: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/62.jpg)
Multinucleated (giant) cellsinfected with reovirus
![Page 63: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/63.jpg)
INCLUSION BODIES POX VIRUS
![Page 64: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/64.jpg)
ANIMAL CELL CULTURES• Primary cell lines
–Tissues• Diploid cell lines
–Human embryos• Continuous cell lines
– Cancerous cells
![Page 65: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/65.jpg)
“...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...”
![Page 66: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/66.jpg)
![Page 67: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/67.jpg)
VIRAL IDENTIFICATION METHODS
• Electron microscopy• Serological
–Specific antibodies • Molecular biology
–Nucleic acid sequences
![Page 68: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/68.jpg)
![Page 69: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/69.jpg)
VIRAL MULTIPLICATION• Viral genes
–Viral proteins–A few enzymes (if any) usually involved with viral nucleic acid replication
![Page 70: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/70.jpg)
VIRAL MULTIPLICATION (cont.)
• Infected cell provides:–Enzymes and machinery for viral nucleic acid and protein synthesis
–Energy
![Page 71: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/71.jpg)
![Page 72: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/72.jpg)
![Page 73: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/73.jpg)
![Page 74: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/74.jpg)
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
![Page 75: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/75.jpg)
LYSOGENIC (TEMPERATE) PHAGES
• Upon infection phage inserts its DNA into the host chromosome (prophage)
• Prophage genes may alter host cell characteristics by transduction
![Page 76: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/76.jpg)
TRANSDUCTION• Generalized
–Phage picks up, randomly, fragments of host DNA instead of phage’s DNA
–May transfer any gene
![Page 77: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/77.jpg)
TRANSDUCTION (cont.)• Specialized
–Phage DNA that has been integrated to host DNA is exised along with a few adjacent host genes
![Page 78: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/78.jpg)
LYSOGENIC PHAGES (cont.)• Toxins produced by:
–Corynebacterium diphteriae–Streptococcus pyogenes–Clostridium botulinum
![Page 79: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/79.jpg)
VIRAL MULTIPLICATION• Attachment• Penetration• Biosynthesis• Maturation• Release
![Page 80: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/80.jpg)
![Page 81: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/81.jpg)
![Page 82: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/82.jpg)
![Page 83: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/83.jpg)
![Page 84: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/84.jpg)
![Page 85: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/85.jpg)
![Page 86: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/86.jpg)
![Page 87: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/87.jpg)
ONCOGENIC VIRUSES• Viral nucleic acid gets
integrated into host genome• Alteration of cellular growth
genes
![Page 88: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/88.jpg)
LATENT VIRAL INFECTIONS
• Virus/host equilibrium–Herpes viruses
•Cold sores•Shingles (chicken pox)
![Page 89: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/89.jpg)
SLOW VIRAL INFECTIONS• Virus builds up gradually• Usually fatal
–Subacute sclerosing panencephalitis
![Page 90: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/90.jpg)
PRIONS• Protein• Undetectable nucleic acid?, a
bacterium?–Neurological diseases–Creutzfeldt-Jacob disease–Mad cow disease
![Page 91: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/91.jpg)
HOST CELL DEFENSES
![Page 92: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/92.jpg)
INTERFERON (IFN)• Antiviral proteins (AVP)
produced by virus-infected cells
• Interfere with viral multiplication
![Page 93: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/93.jpg)
![Page 94: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/94.jpg)
INTERFERON (cont.)• Host-cell specific• Not virus specific• Short lived• No effect on infected cells
![Page 95: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/95.jpg)
INTERFERON TYPES• Alpha (IFN• Beta (IFN• Gamma (IFN)
![Page 96: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/96.jpg)
INTERFERON ACTIVITY• IFNs diffuse and gain
entrance to non-infected neighboring cells
• Induce synthesis of antiviral proteins
![Page 97: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/97.jpg)
INTERFERON ACTIVITY • Antiviral proteins:
–Destruction of viral mRNA–Inhibit translation of viral mRNA
–Inhibit polypeptide elongation
![Page 98: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/98.jpg)
RABBITS AND MYXOMATOSIS
![Page 99: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/99.jpg)
AUSTRALIA
• Introduced Rabbits First arrived in 1778 from Europe
• Spread 125 Km/year• Soon became a pest
![Page 100: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/100.jpg)
MYXOMATOSIS• Caused by a poxvirus• Mild infection in Australian
native rabbits• Fatal infection in the
introduced European rabbits
![Page 101: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/101.jpg)
TRANSMISSION OF MYXOMATOSIS
• Mosquito• Flea• Direct contact
![Page 102: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/102.jpg)
MYXOMA VIRUS IN AUSTRALIA
• Introduced in the Summer 1950-1951
• By 1956 the European rabbit population dropped 90%
![Page 103: Viruses](https://reader035.vdocument.in/reader035/viewer/2022062521/5681566b550346895dc41ed5/html5/thumbnails/103.jpg)
MYXOMA VIRUS IN AUSTRALIA (cont.)
• As time went on:• Rabbit population began to
recover• Appearance of less virulent
viruses• Appearance of more resistant
rabbits