Chapter 13-Viruses of Bacteria

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Chapter 13-Viruses of Bacteria
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General Characteristics of all viruses

• Contain a single type of nucleic acid
• Contain a protein coat
• Obligate intracellular parasites
• Are viruses the only obligate intracellular
  parasites?

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History began with the Tobacco Mosaic Virus (TMV)

• 1886 Aldolf Mayer showed that a virus was
  transmissable between plants
• 1892 Iwanowski tried to isolate it by filtering
  with porcelain filter

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Sizes of viruses
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Polyhedral virus

• Capsid coat made of capsomeres
• Nucleic acid inside

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Parts of a virus
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Relationship of virus with host cell
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Shapes of a virus
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Bacterial viruses

• Known as bacteriophages or phages
• Two different life cycles
• Lytic cycle (virulent)-results in lysis of the
  cell
• Lysogenic cycle (temperate)-may result in lysis
  of the cell or the virus becomes a permanent part
  of the chromosome by integrating

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T4 phage replication
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Lambda Phage
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(No Transcript)
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Lambda integrates into the chromosome
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Properties conferred by prophage
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Some phage are filamentous
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Replication of filamentous phage
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M13 is ssDNAhow does it replicate the ssDNA?
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Chapter 14 Animal Viruses
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How do animal viruses differ from bacterial
viruses?

• Attachment
• Replication of nucleic acid
• Uncoating
• Exit by budding

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Entry by membrane fusion
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Entry by endocytosis
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Replication of nucleic acid
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Release by budding
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Persistant infections

• Virus is continually present in the body,
  released by budding
• Three categories
• Latent infections
• Chronic infections
• Slow infections

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Latent Infections

• Persistant infection with symptomless period
  followed by reactivation of virus and symptoms
• Herpesviridae
• Herpes simplex virus -1
• Herpes simplex virus -2

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Latent Viral infections
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DNA Animal Viruses

• Herpesviridae (dsDNA, enveloped virus)
• -simplex 1(cold sores)
• -simplex 2 (genital herpes)
• -chicken pox, shingles
• -epstein barr

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Herpes Simplex virus-1
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HSV-1 reactivation
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Herpes simplex-1

• HHV-1 causes fever blisters, HHV-2 genital herpes
• Symptoms fluid filled skin lesions
• Treatment Acyclovir

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Varicella (chickenpox) and Herpes Zoster
(Shingles)

• HHV-3 causes chicken pox and latent activation
  known as shingles
• Acquired by respiratory route, 2 weeks later see
  vesicles on skin
• Vaccine established in 1995 for chickenpox

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Epstein Barr

• Causes infectious mononucleosis
• Acquire by saliva, incubation period is 4-7 weeks
• Identify by
• -lobed lymphocytes
• -heterophile antibodies
• -fluorescent antibody tests

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Chronic infections

• Infectious virus present at all times
• Disease may be present or absent
• Best example is Hepatitis Type B virus
• Carriers produce virus detected in blood, saliva,
  and semen
• Unique replication of dsDNA

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Chronic Viral infections
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Hepadnaviridae

• dsDNA, enveloped
• Hepatitis B
• -passes through intermediate stage (RNA)
• -three particles in blood
• Dane
• filamentous
• sphericle
• -exposure through blood/body fluids

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Hepatitis B

• Incubation period is 12 weeks
• 10 of cases become chronic, mortality rate is
  less than 1
• About 40 of the chronic cases die of liver
  cirrhosis

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Slow Infections

• Infectious agent increases in amount over a long
  time during which there are no symptoms
• Examples are HIV found in the Retroviridae family
• Retroviruses use reverse transcriptase to
  replicate ssRNA

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Retrovirus
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Viruses and tumors

• dsDNA viruses are most common to cause
  viral-induced tumors
• Cancer is result of integration of viral genes
  into the host chromosome
• Transforming genes are called oncogenes
• Examples papillomavirus, herpesvirus

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Viruses associated with cancers
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Viruses can alter their genome by reassortment
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Orthomyxoviridae-multiple strands of (-)RNA

• Influenza virus
• Consists of 8 segments of RNA
• Envelope has H spikes (hemagglutinin) and N
  spikes (neuraminidase)
• Incubation is 1-3 days
• Symptoms include chills, fever, headache, muscle
  aches, may lead to cold-like symptoms

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Influenza virus
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Ways to study viruses

• Since viruses grow in living cells.need a live
  cell to culture them
• Cell culture/tissue culture
• Embryonated chicken eggs

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Cell Culture
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Quantitation of viruses
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Proteinaceous infectious particles PRIONS

• 1982 Stanley Prusiner proposed that there were
  infectious proteins
• Caused the disease scrapie in sheep
• Caused the mad-cowdisease in 1987
• Human forms suggest a genetic component

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Prions

• Contain no nucleic acid
• Abnormal protein promotes conformational change
  to normal protein
• Results in damage to neuronstransmissable
  spongiform encephalopahthies

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Brain with spongiform encephalopathy
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Infections caused by prions
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Mechanism of prion replication
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Picornaviridae () ssRNA

• Hepatitis A
• -obtain through fecal-oral route, enters GI
  tract and multiplies
• -incubation period is 4 weeks
• -symptoms include anorexia, malaise, nausea,
  diarrhea, abdominal discomfort, fever, and chills
  lasting 2-21 days

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Rhabdoviridae (-)ssRNA, enveloped

• Rabies virus
• -enters the skin and multiplies in skeletal
  muscle and connective tissue
• -virus travels along nerves to the CNS causing
  encephalitis

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Flaviviridae () ssRNA, enveloped

• Hepatitis C virus
• Obtain from blood/body fluids
• Incubation period averages 6 weeks
• Hard to screen blood for the virus
• 85 of all cases become chronic

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Pathology of rabies
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Retroviridae-multiple strands of (-)RNA

• HIV
• -infects Helper T cells
• -requires the enzyme reverse transcriptase
• -integrates as a provirus
• -is released by budding, or lyses the cell