Download Viruses: Bacterial and Animal

Chapter 13-Viruses of Bacteria
General Characteristics of all viruses
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Contain a single type of nucleic acid
Contain a protein coat
Obligate intracellular parasites
Are viruses the only obligate intracellular
parasites?
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
Sizes of viruses
Polyhedral virus
• Capsid coat made of
capsomeres
• Nucleic acid inside
Parts of a virus
Relationship of virus with host cell
Shapes of a virus
Bacterial viruses
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Known as bacteriophages or phages
Two different life cycles
1. Lytic cycle (virulent)-results in lysis of the
cell
2. Lysogenic cycle (temperate)-may result in
lysis of the cell or the virus becomes a
permanent part of the chromosome by
integrating
T4 phage replication
Lambda Phage
Lambda integrates into the chromosome
Properties conferred by prophage
Some phage are filamentous
Replication of filamentous phage
M13 is ssDNA…how does it
replicate the ssDNA?
Chapter 14: Animal Viruses
How do animal viruses differ
from bacterial viruses?
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Attachment
Replication of nucleic acid
Uncoating
Exit by budding
Entry by membrane fusion
Entry by endocytosis
Replication of nucleic acid
Release by budding
Persistant infections
• Virus is continually present in the body,
released by budding
• Three categories
– Latent infections
– Chronic infections
– Slow infections
Latent Infections
• Persistant infection with symptomless
period followed by reactivation of virus and
symptoms
• Herpesviridae
– Herpes simplex virus -1
– Herpes simplex virus -2
Latent Viral infections
DNA Animal Viruses
• Herpesviridae (dsDNA, enveloped virus)
-simplex 1(cold sores)
-simplex 2 (genital herpes)
-chicken pox, shingles
-epstein barr
Herpes Simplex virus-1
HSV-1 reactivation
Herpes simplex-1
• HHV-1 causes fever
blisters, HHV-2
genital herpes
• Symptoms: fluid filled
skin lesions
• Treatment: Acyclovir
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
Epstein Barr
• Causes infectious
mononucleosis
• Acquire by saliva,
incubation period is 4-7
weeks
• Identify by
-lobed lymphocytes
-heterophile antibodies
-fluorescent antibody tests
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
Chronic Viral infections
Hepadnaviridae
• dsDNA, enveloped
• Hepatitis B
-passes through
intermediate stage (RNA)
-three particles in blood
Dane
filamentous
sphericle
-exposure through
blood/body fluids
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
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
Retrovirus
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
Viruses associated with cancers
Viruses can alter their genome by
reassortment
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
Influenza virus
Ways to study viruses
• Since viruses grow in living cells….need a
live cell to culture them
– Cell culture/tissue culture
– Embryonated chicken eggs
Cell Culture
Quantitation of viruses
Proteinaceous infectious
particles: PRIONS
• 1982 Stanley Prusiner proposed that there
were infectious proteins
• Caused the disease “scrapie” in sheep
• Caused the “mad-cow”disease in 1987
• Human forms suggest a genetic component
Prions
• Contain no nucleic acid
• Abnormal protein promotes conformational
change to normal protein
• Results in damage to
neurons…transmissable spongiform
encephalopahthies
Brain with spongiform
encephalopathy
Infections caused by prions
Mechanism of prion replication
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
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
Flaviviridae (+) ssRNA, enveloped
• Hepatitis C virus
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Obtain from blood/body fluids
Incubation period averages 6 weeks
Hard to screen blood for the virus
85% of all cases become chronic
Pathology of rabies
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