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.

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.

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.

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 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 Orthomyxovirus Influenza 5 serotypes: 1, 2, 3, 4a and 4b Closely related to Mumps virus Parainfluenza Causes a sizable epidemic each year. can be grown in tissue culture. Inclusion bodies can be present. Respiratory Syncytial (RSV)