Viruses are a common cause of respiratory infections. Influenza virus is an RNA virus that causes influenza and can evolve through antigenic drift or shift, resulting in seasonal epidemics or pandemics. Other respiratory viruses include rhinoviruses, coronaviruses, parainfluenza viruses, respiratory syncytial virus (RSV), and adenoviruses. These viruses are diagnosed through antigen detection, virus isolation, or serology and treated symptomatically, though vaccines exist for some viruses. SARS is a coronavirus that emerged in 2002 and can cause severe respiratory illness.

1. Respiratory Viruses

2. Viruses Associated with
Respiratory Infections
Syndrome Commonly
Associated Viruses
Coryza Rhinoviruses,
Coronaviruses
Influenza Influenza viruses
Croup Parainfluenza
viruses
Bronchiolitis RSV
Bronchopneum
onia
Influenza virus,
RSV, Adenoviruses

3. Influenza Virus
 RNA virus
 Enveloped virus, with haemagglutinin
(HA) and neuraminidase (NA) spikes
 3 types: A, B, and C
 Type A undergoes antigenic shift and
drift.
 Type B undergoes antigenic drift only
 Type C is relatively stable
(Courtesy of Linda Stannard,
University of Cape Town, S.A.)

4. Influenza A Virus
 Antigenic shift is an abrupt
change of the HA due to
genetic reassortment: results in
pandemics
 Antigenic drift is a gradual
change in the HA and NA
proteins: results in epidemics

5. Reassortment
Avian H3 Human H2
Human H3
Reassortment of the H and N
genes between human and
avian influenza viruses
through a third host.

6. Epidemiology
Epidemics
 Epidemics of influenza A and B arise due to minor
antigenic drifts as a result of mutation
Pandemics
 Due to antigenic shift a virus with a new
haemagglutinin subtype emerges
 The population has no immunity against the new strain
 Three antigenic shifts occurred in the 20th
century

7. 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.

8. Influenza Virus Replication

9. Avian Influenza
H5N1
 An outbreak of Avian Influenza H5N1 in Hong Kong in
1997
 The source of the virus was probably infected chickens
 Was controlled by a mass slaughter of chickens in the area
H9N2
 Several cases of human infection occurred in Hong Kong
and Southern China in 1999
 The disease was mild and all patients made a complete
recovery

10. Symptoms
 Usually much more severe than, the "common cold."
 “Incubation period." 1-2 days
 Fever (up to 104° F)
 Chills
 Muscle aches and pains
 Sweating
 Dry Cough
 Nasal congestion
 Sore throat
 Headache
 Malaise & Fatigue
 Some or all of these symptoms may be present
 Illness can last for up to 1-2 weeks, although fever generally
lasts only 3-8 days.

11. Complications
 Bacterial pneumonia
 Influenza can damage the lining of the
respiratory tract and bacteria establish an
infection
 Streptococcus pneumoniae and Staphylococcus
aureus are the common causes.
 Pneumonia caused by the virus itself is less
common

12. Laboratory Diagnosis
Specimens
 Nasopharyngeal aspirates & throat washings
Detection of Antigen
 By IFT and ELISA: a rapid diagnosis
Virus Isolation
Serology
 CFT most widely used.
 EIA detect type-specific antibodies

13. Management
 Amantidine
 Rimantidine
 Ribavirin
 Neuraminidase
inhibitors

14. Prevention
 Vaccination with an inactivated
trivalent vaccine, consisting of one A
H3N2 strain, one A H1N1 strain, and
one B strain
 May be 30-90% protective
 Given to debilitated, elderly and
immunocompromized individuals
 Amantidine prophylaxis
 WHO Global Surveillance
Nasal Spray

15. Common Cold Viruses
 Common colds: one-third to one-half of all
acute respiratory infections in humans
 Rhinoviruses (30-50%)
 Coronaviruses (10-30%)
 Others:
 Adenoviruses
 Enteroviruses
 RSV
 Influenza, and parainfluenza viruses

16. Rhinovirus
 ssRNA virus
 Picornavirus family
 Acid-labile
 At least 100 serotypes are
known
Reconstructed Image of rhinovirus
particle (Institute for Molecular Virology)

17. Coronavirus
 ssRNA Virus
 Enveloped,
pleomorphic
morphology

18. Severe Acute Respiratory
Syndrome (SARS)
 In late 2002: first observed in Southern
China (Guangdong Province).
 Now been reported in Asia, North
America, and Europe
 The initial outbreak of SARS peaked in
April 2003 and by June had tailed off.
By that time, there had been about
8,000 cases worldwide and 775 deaths.

20. SARS
Is characterized by:
 Fever above 38o
C (100.4o
F) headache,
general malaise and aches.
 Initially mild respiratory symptoms
 Dry non-productive cough & dyspnea
 Respiratory distress leads to death in
3-30% of cases.

21. Day 5 Day 10
Day 13 Day 15

22.  The virus was grown on monkey Vero E6
cells in tissue culture and a new
coronavirus (SARS-coV) was identified
 Reduction in lymphocyte numbers
 Raised aminotransferase activity which
indicates damage to the liver.
SARS

23. CDC recommendations:
 Chest radiograph
 Blood cultures
 Sputum Gram's stain and culture
 Testing for viral respiratory pathogens, notably
influenza A and B and RSV.
 Legionella and pneumococcal urinary antigen
testing
SARS: Lab
Diagnosis

24. Treatment
 Suspected SARS patient should be
isolated and quarantined.
 Management of symptoms
 No vaccine against the SARS virus.
 A major problem with live virus
vaccine is antigenic shift and
unpredictable outcomes

25. Parainfluenza Virus
 ssRNA virus
 Enveloped
 5 serotypes: 1, 2, 3, 4a and 4b
 Closely related to Mumps
virus
(Linda Stannard, University of Cape Town, S.A.)

26. Clinical Manifestations
Croup (laryngotraheobroncitis)
 The most common manifestation
 Bronchiolitis
 Pneumonia
 Flu-like tracheobronchitis
 Coryza-like illnesses

27. Laboratory Diagnosis
 Specimens
 Detection of Antigen
 Virus Isolation
 Serology
 Symptomatic Treatment
 No vaccine is available.
Management

28. Respiratory Syncytial Virus
(RSV)
 ssRNA eveloped virus
 Paramyxovirus family
 Causes a sizable epidemic each year

29. Clinical Manifestations
 Most common cause of severe lower
respiratory tract disease in infants
 Bronchiolitis (50-90%)
 Bronchopneumonia (5-40% )
 Croup (10% of all cases)
 Coryza-like illness or bronchitis: in older
children and adults

30. Laboratory Diagnosis
Specimens
 Nasopharyngeal aspirates & throat washings
Detection of Antigen
Virus Isolation
Serology

31. Treatment and Prevention
 Aerosolised ribavirin
 There is no vaccine available
 RSV immunoglobulin for high risk
group infants

32. Adenovirus
 ds DNA virus
 non-enveloped
 At least 47 serotypes
(Linda Stannard, University of Cape Town, S.A.)

33. Clinical Syndromes
Pharyngitis
Pharyngoconjunctival fever
Acute respiratory disease of recruits
Pneumonia
Follicular conjunctivitis
Epidemic keratoconjunctivitis
Pertussis-like syndrome
Acute haemorrhaghic cystitis
Acute infantile gastroenteritis
Intussusception
Severe disease in AIDS
Meningitis

34. Laboratory Diagnosis
Specimens
 Nasopharyngeal aspirates, throat washings & feces
Detection of Antigen
Virus Isolation
Serology

35. Treatment and Prevention
 A vaccine is available against Adult
Respiratory Distress Syndrome.
 Consists of live adenovirus 4, 7, and 21 in
enterically coated capsules.
 Given to new recruits into various arm
forces around the world.