Virology presentation

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Virology presentation

• Group 8
• Pcl II

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Poliovirus
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Poliovirus , a highly contagious virus that
causes the medical condition polio
(poliomyelitis) is a human enterovirus and member
of the family of Picornaviridae.
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Virus classification

• Group Group IV (() ssRNA)
• Order Picornavirales
• Family Picornaviridae
• Genus Enterovirus
• Species Human enterovirus C
• Scientific name Poliovirus

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• There are three serotypes of poliovirus, PV1, PV2,
  and PV3 each with a slightly different capsid pr
  otein. Capsid proteins define cellular receptor
  specificity and virus antigenicity. PV1 is the
  most common form encountered in nature, however
  all three forms are extremely infectious.

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General properties Poliovirus particle are
typical enterovirus. They are inactivated when
heated at 550c for 30min,by a high chlorine
concentration,by formaldehyde and ultra violet
light. Poliovirus are not affected ether or
sodium deoxycholate
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Structure

• RNA genome.
• protein capsid.
• single-stranded positive-sense.
• RNA genome that is about 7500 nucleotides long.
• The viral particle is about 30 nanometres in
  diameter with icosahedral symmetry.
• non-enveloped .

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Replication cycle

• The virus first multiplies in tonsil, the lymph
  nodes of the neck, Peyer s paches, and the small
  intestine.
• The central nervous system may be invaded by way
  of the circulating blood. Large amounts of
  anti-body are necessary to prevent passage of the
  virus along nerve fiber.

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• Poliovirus can spread along axons of peripheral
  ner-ves to the central nervous system, along the
  fibers of the lower motor neurons to the spinal
  cord or the br-ain.
• Virus invades certain types of nerve cell, and
  may da-mage or completely destroy these cells for
  its intracell-ular multiplication.

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Events in replication

• 1. Binding to the cell surface receptor CD155.
• 23.Taken via endocytosis and decapsulated and
  then the viral RNA released.
• 4. Translation of the viral RNA occurs and
  polyprotein is cleaved yielding mature viral
  proteins.
• 5. Double stranded replicative form RNA is
  produced and many positive strands RNA copies are
  produced from single negative strand.

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• 6. Newly synthesized positive sense RNA molecules
  serve as templates for translation of more viral
  proteins or can be enclosed in a capside (capside
  assembly)
• 7. Lysis of infected cell results in release of
  infections progeny virions (liberation of
  virions)

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Pathogenesis ? Pathology The mouth is the portal
of entry of the virus and primary multiplication
takes place in the oropharynx or intestine. The
virus is regularly present in the throat and in
the stools before the onset of illness. The virus
may be found in the blood of patients with
nonparalytic poliomyelitis. Ab to the virus
appear early in the disease, usually before
paralysis occurs

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Transmission

• Fecal oral route
• via hands and objects
• via food and water

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Clinical findings Abortive poliomyelitis Nonparal
ytic poliomyelitis Paralytix poliomyelitis Progres
sive postpoliomylitis muscle atrophy
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Clinical Manifestations

• Most infections asymptomatic, 95
• Abortive polio (minor illness), 5 fever,
  malaise, sore throat, myalgia, headache)
• Aseptic meningitis (non paralytic polio), 1
• Paralytic polio (major illness), 0.1 asymetric
  flaccid paralysis / paresis. Lower, or upper
  extremities, thoracic, abdominal, bulbar.
• Involvement spinal cord anterior horn cells,
  motor cortex, dorsal root ganglia
• neurologic sequela (2/3)
• Post-polio syndrome progressive atrophy years
  later

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• Perhaps the first written record of a virus
  infection consists of a heiroglyph from Memphis,
  drawn in approximately 1400BC, which depicts a
  temple priest called Siptah showing typical
  clinical signs of paralytic poliomyelitis

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Victims of paralytic polio
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Child with polio sequelae 
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Laboratory diagnosis The virus may be recovered
from throat swabs, rectal swabs, or stool
samples. Specimens should be kept frozen during
transit to the laboratory Cultures of human or
monkey cells Paired serum specimens are required
to show rise in antibody titer during the course
of disease.

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Laboratory Diagnosis

• Virus Isolation
• Mainstay of diagnosis of poliovirus infection
• poliovirus can be readily isolated from throat
  swabs, faeces, and rectal swabs, but rarely from
  the CSF
• Can be readily grown and identified in cell
  culture
• Requires molecular techniques to differentiate
  between the wild type and the vaccine type
• Serology
• Very rarely used for diagnosis since cell
  culture is efficient. Occasionally used for
  immune status screening for immunocompromised
  individuals

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Immunity Immunity is permanent to the type
cau-sing the infection. Passive immunity is
transferred from mother to offspring, which
gradually disappear during the first 6 months of
life. Virus-neutralizing antibody forms soon
after exposure to the virus, often before the
onset of illness.

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Epidemiology Poliomyelitis occurs worldwide
year-round in tropics and during summer and fall
in tem-perate zone. Winter outbreaks are
rare. The disease occurs in all age groups ,but
chil-dren are more susceptible than adult because
of the acquired immunity of the adult
popula-tion. Human are the only known reservoir
of infect-ion.

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Prevention ? control Both live-virus and
killed-virus vaccines are avail-able . They
induce antibody and protect the central nervous
system from subsequent invasion by wild virus. A
potential limiting factor for oral vaccine is
interfer-ence, and for vaccine-associated
disease, a switch to the use of only inactivated
poliovaccine (four doses) for children Immune
globulin can provide protection for a few weeks
against the paralytic disease but does not
prevent subclinical infection. The application of
recombinant DNA

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Vaccines Available

• Intramuscular Poliovirus Vaccine (IPV)
• consists of formalin inactivated virus of all 3
  poliovirus serotypes (Salk)
• Produces serum antibodies only does not induce
  local immunity and thus will not prevent local
  infection of the gut
• However, it will prevent paralytic poliomyelitis
  since viraemia is essential for the pathogenesis
  of the disease
• Oral Poliovirus Vaccine (OPV)
• Consists of live attenuated virus of all 3
  serotypes (Sabin).
• Produces local immunity through the induction of
  an IgA response as well as systemic immunity
• Rarely causes paralytic poliomyelitis, around 1
  in 3 million doses

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• Most countries use OPV because of its ability to
  induce local immunity and also it is much cheaper
  to produce than IPV
• The normal response rate to OPV is close to 100.
• OPV is used for the WHO poliovirus eradication
  campaign
• Because of the slight risk of paralytic
  poliomyelitis, some Scandinavian countries have
  reverted to using IPV. Because of the lack of
  local immunity, small community outbreaks of
  poliovirus infections have been reported