Respiratory Viruses

Viruses Associated with Respiratory Infections

Syndrome Commonly Associated Viruses

Coryza Rhinoviruses, Coronaviruses

Influenza Influenza viruses

Croup Parainfluenza viruses

Bronchiolitis RSV

Bronchopneumonia

Influenza virus, RSV, Adenoviruses

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.)

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

Reassortment

Avian H3 Human H2

Human H3

Reassortment of the H and N genes between human and

avian influenza viruses through a third host.

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

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.

Influenza Virus Replication

Avian InfluenzaH5N1 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

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.

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

Laboratory DiagnosisSpecimens Nasopharyngeal aspirates & throat washings Detection of Antigen By IFT and ELISA: a rapid diagnosis

Virus IsolationSerology CFT most widely used. EIA detect type-specific antibodies

Management

Amantidine Rimantidine Ribavirin Neuraminidase

inhibitors

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

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

Rhinovirus

ssRNA virus Picornavirus family Acid-labile At least 100 serotypes are

known

Reconstructed Image of rhinovirus particle (Institute for Molecular Virology)

Coronavirus

ssRNA Virus Enveloped,

pleomorphic morphology

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.

SARS

Is characterized by: Fever above 38oC (100.4oF) headache,

general malaise and aches. Initially mild respiratory symptoms Dry non-productive cough & dyspnea Respiratory distress leads to death in

3-30% of cases.

Day 5 Day 10

Day 13 Day 15

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

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

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

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.)

Clinical Manifestations

Croup (laryngotraheobroncitis) The most common manifestation

Bronchiolitis Pneumonia Flu-like tracheobronchitis Coryza-like illnesses

Laboratory Diagnosis Specimens Detection of Antigen Virus Isolation Serology

Symptomatic Treatment No vaccine is available.

Management

Respiratory Syncytial Virus (RSV)

ssRNA eveloped virus Paramyxovirus family Causes a sizable epidemic each year

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

Laboratory Diagnosis

Specimens Nasopharyngeal aspirates & throat washings Detection of Antigen Virus IsolationSerology

Treatment and Prevention

Aerosolised ribavirin There is no vaccine available

RSV immunoglobulin for high risk group infants

Adenovirus

ds DNA virus non-enveloped At least 47 serotypes

(Linda Stannard, University of Cape Town, S.A.)

Clinical SyndromesPharyngitis Pharyngoconjunctival feverAcute respiratory disease of recruits Pneumonia Follicular conjunctivitis Epidemic keratoconjunctivitisPertussis-like syndrome Acute haemorrhaghic cystitis Acute infantile gastroenteritis IntussusceptionSevere disease in AIDS Meningitis

Laboratory Diagnosis

Specimens Nasopharyngeal aspirates, throat washings & fecesDetection of Antigen Virus IsolationSerology

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.