PowerPoint Presentation - Epidemiology and Prevention of Viral Hepatitis A to E:

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WHAT IS A VIRUS? Viruses may be defined as
acellular organisms whose genomes consist of
nucleic acid, and which obligately replicate
inside host cells using host metabolic machinery
to different extents, to form a pool of
components which assemble into particles called
virions.
F A virus differs from a cell in three
fundamental ways i A virus usually has only a
single type of nucleic acid serving as its
genetic material. This can be single or double
stranded DNA or RNA ii Viruses contain no
enzymes of energy metabolism, thus cannot make
ATP iii Viruses do not encode sufficient
enzymatic machinery to synthesize their component
macromolecules, specifically, no protein
synthesis machinery.
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Fundamentally then, a virus is

• A package of genetic information protected by a
  protein shell for delivery into a host cell to be
  expressed and replicated

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Viruses are distinguished from other obligate
parasites, some of which are even simpler than
viruses MYCOPLASMA Small bacterium that grows
only in complex medium or attached to eucaryotic
cells. CHLAMYDIA Obligate intracellular
bacterial parasite which depends on eucaryotic
cell for energy. PROTOZOA Obligate intracellular
parasite that replicate within eucaryotic
cells. VIROID Infectious agents of plants that
exist as naked nucleic acid (circular single
stranded (ss) ssRNA). HEPATITIS DELTA VIRUS
(HDV) Viroid-like agent whose replication is
dependent upon HBV.
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PRION (proteinacious infectious agent)
Hypothesized identity of the unconventional slow
viruses (such as the Kuru, Scrapie and Mad cow
disease agents). No nucleic acid is known to be
required for prion function. They are thought by
many to consist solely of protein and perhaps
lipids. Study of these agents has resulted in 2
nobel prize awards.
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• Recognition of viruses
• F How long viruses have been within our midst?
• 1500 BC Leg deformities indicative of
  poliomyelitis, pock marks indicative of smallpox
  and.

"Virus" is from the Greek meaning for "poison"
and was initially described by Edward Jenner in
1798.
During the 1800's, all infectious agents were
considered to be viruses until Koch developed
pure culture techniques which allowed the
separation and growth of bacteria. In the late
1800's Bacteria were purified and established as
disease causing agents. It then became possible
to distinguish them from the "filterable agents",
those able to pass through special filters
designed to prevent the passage of bacteria. The
first viruses described were foot and mouth
disease (a picornavirus), 1898, Yellow fever (a
flavivirus), 1900, Rous sarcoma virus (an
oncogenic retrovirus), 1906.
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Viral diseases have played a major role in human
history over whatever time scale we choose to
explore Over the past 1000 years Smallpox and
measles were brought to North and South America
by early European explorers/conquerers. These
diseases, for which the native American
populations had no acquired partial immunity,
killed large fractions of the populations, and
were a major factor in the decimation of these
societies.
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Over the past 10 years As the global HIV
epidemic continues, sporadic cases and outbreaks
in humans of some non-human host viruses such as
Ebola and Hanta raise the concern about future
epidemics by other viruses in the new century.
FourCorners Virus (Hanta)
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THE DISCIPLINE OF VIROLOGY The study of virology
inherently involves a merging together of what
has traditionally been thought of as two separate
"kinds" of science basic and applied science. We
want to figure out how viruses are transmitted,
how they replicate, and how the host organism
responds. We also want to figure out how to
prevent transmission, how to interfere with virus
replicaton, and how to confer immunity on the
host. The "applied" follows from, and is
dependent upon, the "basic" in a quite direct
way. Virology as it is studied today, is
therefore an outgrowth of both
Infectious diseases - because of the recognition
of viral pathogens. Molecular Biology- because
of the usefulness of viruses as probes of cell
and molecular biology and metabolism, and as
vectors with strong potential for gene therapy.
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WHERE WE STAND IN 2001 PREVENTING CONTROLING
CURING VIRAL DISEASES
Smallpox effective vaccine this is the only
viral disease that has been wiped out worldwide
Measles effective vaccine since 1963 this
disease could be eliminated with a world-wide
effort Influenza effective strain-specific
vaccine, but new variant strains emerge
periodically Polio effective vaccine will soon
be the second viral disease wiped out HIV no
vaccine effective drugs, but they are costly and
toxic, plus resistant strains appear. World-wide
spread continues via intimate contact. 50 million
infected thus far Ebola no vaccine important
host species unknown (found recently in chimps
and rodents) outbreaks controllable because
people die quickly and human-human transmission
is via blood Hanta no vaccine rodent host
easy transmission to humans, but outbreaks
controllable We also share the world, and our
bodies, with viruses that cause hepatitis,
respiratory disease, mononucleosis, diarrhea,
genital warts, genital herpes, and some forms of
cancer
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• How are viruses classified ?
• Hierarchical virus classification (order)
  family - subfamily - genus - species -
  strain/type
• All families have the suffix viridae, e.g.
• Poxviridae
• Herpesviridae
• Parvoviridae
• Retroviridae
• Genera have the suffix virus. Within the
  Picornaviridae there are 5 genera
• enterovirus (alimentary tract), species e.g.
  poliovirus 1, 2, 3
• cardiovirus (neurotropic), species e.g.
  mengovirus
• rhinovirus (nasopharyngeal region), species
  e.g. Rhinovirus 1a
• apthovirus (cloven footed animals ), species
  e.g. FMDV-C

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Virus naming and classification Usually based
on data available at the time of
discovery i Disease they are associated with,
e.g. Poxvirus, Hepatitis virus, HIV, measles
virus ii Cytopathology they cause,
e.g. Respiratory Syncytial virus,
Cytomegalovirus iii Site of isolation,
e.g. Adenovirus, Enterovirus,
Rhinovirus iv Places discovered or people that
discovered them, e.g. Epstein-Barr virus, Rift
Valley Fever v Biochemical features,
e.g. Retrovirus, Picornavirus, Hepadnavirus
RSV
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These naming conventions can lead to confusion
later, e.g., viral hepatitis is caused by at
least 6 different viruses
10-20 of cases of presumed viral hepatitis are
still not accounted for
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Thus,

• Different viruses can cause (nearly) the same
  symptoms. e.g., the hepatitis viruses
• However, different members of the same group can
  cause different symptoms. e.g., the herpes viruses

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Herpesviruses

• HSV Herpes Simplex Virus Cold sores (type 1),
  Genital lesions (type 2)
• VZV Varicella Zoster Virus Chicken pox
• CMV Cytomegalovirus Mononucleosis
• EBV Epstein-Barr Virus Mononucleosis, Burkitts
  lymphoma, Nasopharyngeal carcinoma
• and HHV-6, HHV-7, HHV-8..(Human HerpesVirus-)

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Virus Classification is now based principally on
analysis of the particle Morphology by
electron microscopy Serology antigenic
cross-reactivity Genetic material form
of nucleic acid ssDNA ( or - strand)
dsDNA ssRNA ( or - strand) dsRNA
segmented RNA genetic organization
sequence homology DNA sequence
Hybridization
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Animal virus classification DNA Viruses
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Molluscum Contagiosum
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Plus Sense RNA Viruses
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Minus Sense RNA Viruses