Respiratory Viruses

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Respiratory Viruses Respiratory diseases occur
most frequently in colder weather, especially in
raining season, and in cases of overcrowding.
Causes of sever viral respiratory illnesses in
developing countries include measles virus,
influenza and parainfluenza viruses, and
respiratory syncytial viruse.
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• 1- Measles virus
• Measles virus belongs to the family
  Paramyxovirus.
• VIRUS
• It is a single stranded RNA spherical particle
• with helical capsid symmetry.
• It is surrounded by an envelope.
• The virus can be grown in human and animal tissue
  culture cells.

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• Transmission and pathogenecity
• In developing countries measles is a serious and
  fetal disease in non immune young children,
  especially with malnutrition and immune
  suppressive children.
• The virus is highly infectious and spread mainly
  by air droplets.

• Clinical features
• Early clinical features include, fever, cough,
  nasal discharge and
  conjunctivitis followed by a rash.
• Complications which develop due to sever measles
  and ,or, secondary bacterial or viral infection
  include bronchopneumonia and diarrhea,
  conjunctivitis which may lead to ulcerative
  keratitis and blindness. Anaemia often develops.

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• Prevention
• Usually by immunization with live vaccine at 9
  months old.
• Great caring must be taken when dealing with
  measles samples.
• An efficient cold storage must be used.
• Lab diagnosis
• Measles usually diagnosed clinically. If
  laboratory assist is required, it is recommended
  to take nasopharyngeal specimen and use the
  immunofluorescence technique.

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• 2. Influenza Virus
• RNA virus.
• belong to the family Orthomyxovirus
• enveloped virus
• 3 types A, B, and C
• Type A undergoes antigenic shift and drift.
• Type B undergoes antigenic drift only
• and type C is relatively stable

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• Clinical features
• The clinical features of influenza "flu" include
  fever, chills, tiredness, headache, muscle pain,
  sore throat. Infection is by inhaling the virus.
• Severe case can lead to influenza pneumonia which
  can be fetal.
• Influenza A Virus
• Usually causes a mild febrile illness.
• Death may result from complications such as
  viral/bacterial pneumonia.

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Past Antigenic Shifts

• 1918 H1N1 Spanish Influenza 20-40 million
  deaths
• 1957 H2N2 Asian Flu 1-2 million deaths
• 1968 H3N2 Hong Kong Flu 700,000 deaths
• 1977 H1N1 Re-emergence No pandemic
• At least 15 HA subtypes and 9 NA subtypes occur
  in nature. Up until 1997, only viruses of H1, H2,
  and H3 are known to infect and cause disease in
  humans.

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• Avian Influenza
• H5N1
• An outbreak of Avian Influenza H5N1 occurred in
• Hong Kong in 1997 where 18 persons were infected
  of which 6 died.
• The source of the virus was probably from
  infected chickens and the outbreak was eventually
  controlled by a mass slaughter of chickens in the
  territory.
• However, the strains involved were highly
  virulent for their natural avian hosts.
• H9N2
• Several cases of human infection with avian H9N2
  virus occurred in Hong Kong and Southern China in
  1999.
• The disease was mild and all patients made a
  complete recovery
• Again, there was no evidence of reassortment

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• Laboratory Diagnosis
• This is required at the start of a new epidemic
  so that the virus type and subtype can be
  identified and, if needed a new vaccine is
  prepared.
• Detection of Antigen - a rapid diagnosis can be
  made by the detection of influenza antigen from
  nasopharyngeal aspirates and throat washings by
  IFT and ELISA
• Virus Isolation - virus may be readily isolated
  from nasopharyngeal aspirates and throat swabs by
  egg inoculation and cultural technique.

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• Prevention
• Inactivated vaccines are available against
  influenza A and B.
• The vaccine is normally trivalent, consisting of
  one A H3N2 strain, one A H1N1 strain, and one B
  strain.
• The strains used are reviewed by the WHO each
  year.
• The vaccine should be given to debilitated and
  elderly individuals who are at risk of severe
  influenza infection.
• If however, an epidemic is caused by a new
  subtype, previous immunization is ineffective.

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• 3- Parainfluenza Virus
• ssRNA virus
• belonging to the family Paramyxoviruse
• enveloped, pleomorphic morphology
• 5 serotypes 1, 2, 3, 4a and 4b
• Closely related to Mumps virus

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• Transmission and pathogenicity
• Parainfluenza viruses are highly infectious but
  about 30-50 of infections are without symptoms.
• The most serious Parainfluenza viral infections
  occur in young children. The exudate produced by
  the inflamed cells of the respiratory tract can
  cause obstruction of the larynx and bronchi
  (Croup).
• Type 1 and 2 Parainfluenza viruses are often the
  cause of croup, and infections tend to occur as
  epidemics.
• Parainfluenza type 3 is a major cause of sever
  bronchiolitis and bronchopneumonia in infants.
• Type 4 is of low pathogenicity
• Vaccines against Parainfluenza viruses are not
  yet available.

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• Clinical Manifestations
• Croup (laryngotracheobroncitis) - most common
  manifestation of parainfluenza virus infection.
  However other viruses may induce croup e.g.
  influenza and RSV.
• Other conditions that may be caused by
  parainfluenza viruses include Bronchiolitis,
  Pneumonia.

• Management
• No specific antiviral chemotherapy available.
• Severe cases of croup should be admitted to
  hospital and placed in oxygen tents.
• No vaccine is available.

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• Laboratory Diagnosis
• Detection of Antigen - a rapid diagnosis can be
  made by the detection of parainfluenza antigen
  from nasopharyngeal aspirates and throat
  washings.
• Virus Isolation - virus may be readily isolated
  from nasopharyngeal aspirates and throat swabs.
• Serology - a retrospective diagnosis may be made
  by serology.

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• 4- Respiratory Syncytial Virus (RSV)
• ssRNA virus.
• belong to the Paramyxovirus family.
• Causes a sizable epidemic each year.
• It is surrounded by an envelop.
• RSV can be grown in tissue culture.
• Infected cells joined together in masses called
  syncytia.
• Inclusion bodies can be present.

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• Transmission and pathology
• RSV is a cause of sever and occasionally fetal
  bronchiolitis and pneumonia in infants.
• It can also cause infections of the upper
  respiratory tract.
• A complication of RSV in young children is otitis
  media.
• RSV is highly infectious. It is spread from one
  person to person mainly by droplet infection
• No vaccine against RSV is available at present.
• Breast feeding provides some protection for
  infants.
• responsible for 50-90 of Bronchiolitis and 5-40
  of Bronchopneumonia
• Other manifestations include croup (10 of all
  cases).

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• Infants at Risk of Severe Infection
• Infants with congenital heart disease - infants
  who were hospitalized within the first few days
  of life with congenital disease are particularly
  at risk.
• Infants with underlying pulmonary disease -
  infants with underlying pulmonary disease,
  especially bronchopulmonary dysplasia, are at
  risk of developing prolonged infection with RSV.
• Immunocompromized infants
• children who are immunosuppressed
• or have a congenital immunodeficiency
• disease may develop lower respiratory
• tract disease at any age.

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• Laboratory Diagnosis
• Detection of Antigen - a rapid diagnosis can be
  made by the detection of RSV antigen from
  nasopharyngeal aspirates.
• Virus Isolation - virus may be readily isolated
  from nasopharyngeal aspirates. However, this will
  take several days.
• Serology

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Respiratory Viruses
Features Envelop Nuclic acid Family Virus
virus can be grown in human and animal tissue Enveloped helical RNA Paramyxovirus Measles
3 types A, B, and C Enveloped helical RNA Orthomyxovirus Influenza
5 serotypes 1, 2, 3, 4a and 4b Closely related to Mumps virus Enveloped helical RNA Paramyxovirus Parainfluenza
Causes a sizable epidemic each year. can be grown in tissue culture. Inclusion bodies can be present. Enveloped helical RNA Paramyxovirus Respiratory Syncytial (RSV)