Enveloped virus, with haemagglutinin
(HA) and neuraminidase (NA) spikes
3 types: A, B, and C
Type A undergoes antigenic shift and
Type B undergoes antigenic drift only
Type C is relatively stable
(Courtesy of Linda Stannard,
University of Cape Town, S.A.)
Influenza A Virus
Antigenic shift is an abrupt
change of the HA due to
genetic reassortment: results in
Antigenic drift is a gradual
change in the HA and NA
proteins: results in epidemics
Avian H3 Human H2
Reassortment of the H and N
genes between human and
avian influenza viruses
through a third host.
Epidemics of influenza A and B arise due to minor
antigenic drifts as a result of mutation
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
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.
An outbreak of Avian Influenza H5N1 in Hong Kong in
The source of the virus was probably infected chickens
Was controlled by a mass slaughter of chickens in the area
Several cases of human infection occurred in Hong Kong
and Southern China in 1999
The disease was mild and all patients made a complete
Usually much more severe than, the "common cold."
“Incubation period." 1-2 days
Fever (up to 104° F)
Muscle aches and pains
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.
Influenza can damage the lining of the
respiratory tract and bacteria establish an
Streptococcus pneumoniae and Staphylococcus
aureus are the common causes.
Pneumonia caused by the virus itself is less
Nasopharyngeal aspirates & throat washings
Detection of Antigen
By IFT and ELISA: a rapid diagnosis
CFT most widely used.
EIA detect type-specific antibodies
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
WHO Global Surveillance
Common Cold Viruses
Common colds: one-third to one-half of all
acute respiratory infections in humans
Influenza, and parainfluenza viruses
At least 100 serotypes are
Reconstructed Image of rhinovirus
particle (Institute for Molecular Virology)
Severe Acute Respiratory
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.
Is characterized by:
Fever above 38o
general malaise and aches.
Initially mild respiratory symptoms
Dry non-productive cough & dyspnea
Respiratory distress leads to death in
3-30% of cases.
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.
Sputum Gram's stain and culture
Testing for viral respiratory pathogens, notably
influenza A and B and RSV.
Legionella and pneumococcal urinary antigen
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
5 serotypes: 1, 2, 3, 4a and 4b
Closely related to Mumps
(Linda Stannard, University of Cape Town, S.A.)
The most common manifestation
Detection of Antigen
No vaccine is available.
Respiratory Syncytial Virus
ssRNA eveloped virus
Causes a sizable epidemic each year
Most common cause of severe lower
respiratory tract disease in infants
Bronchopneumonia (5-40% )
Croup (10% of all cases)
Coryza-like illness or bronchitis: in older
children and adults
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.