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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.
Syndrome
Commonly Associated Viruses
Less Commonly Associated Viruses
Corza
Rhinoviruses, Coronaviruses
Influenza and parainfluenza viruses,
enteroviruses, adenoviruses
Influenza
Influenza viruses
Parainfluenza viruses, adenoviruses
Croup
Parainfluenza viruses
Influenza virus, RSV, adenoviruses
Bronchiolitis
RSV
Influenza and parainfluenza viruses,
adenoviruses
Bronchopneumonia
Influenza virus, RSV, Adenoviruses Parainfluenza viruses, measles, VZV, CMV
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.
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.
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.
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
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.
20-40 million deaths
“Spanish Influenza” H1N1 1918
1-2 million deaths
“Asian Flu” H2N2 1957
700,000 deaths
“Hong Kong Flu” H3N2 1968
No pandemic Re-emergence H1N1 1977
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.
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
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.
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.
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
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.
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.
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.
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.
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).
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.
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
Respiratory Viruses
Virus
Family
Nuclic
acid
Envelop
Features
virus can be grown
in human and animal
tissue
3 types: A, B, and C
Measles
Paramyxovirus
RNA
Enveloped
helical
Influenza
Orthomyxovirus
RNA
Enveloped
helical
Parainfluenza
Respiratory
Syncytial (RSV)
Paramyxovirus
Paramyxovirus
RNA
RNA
Enveloped
helical
Enveloped
helical
•5 serotypes: 1, 2, 3,
4a and 4b
•Closely related to
Mumps virus
•Causes a sizable
epidemic each year.
•can be grown in
tissue culture.
•Inclusion bodies
can be present.