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Respiratory tract viruses 

Respiratory tract viruses

Respiratory tract viruses

Malik Peiris



Rhinoviruses—discussion of non-cultivable group C viruses, recently discovered by molecular methods.

Adenoviruses—four additional non-cultivable adenovirus types, 52–55, have recently been reported; adenovirus 14p1 (previously designated 14a) has been spreading in the United States of America and elsewhere and is associated with more severe disease.

Influenza—previous seasonal influenza A H1N1 viruses appear to have been largely replaced by pandemic H1N1 which now cocirculates with seasonal H3N2 and influenza B viruses.

Updated on 31 May 2012. The previous version of this content can be found here.
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date: 30 March 2017

Viral respiratory infections, including rhinovirus, coronavirus, adenovirus, respiratory syncytial virus, human metapneumovirus, parainfluenza viruses, and influenza viruses, are a substantial cause of morbidity worldwide. Transmission occurs through direct contact, contaminated fomites, and large airborne droplets, with long-range transmission by small particle aerosols reported in at least some instances of influenza and severe acute respiratory syndrome (SARS).

Clinical syndromes affect the upper and/or lower respiratory tract, including coryza, pharyngitis, croup, bronchiolitis, and pneumonia. Each syndrome can potentially be caused by a number of viruses, and each respiratory virus can be associated with different clinical syndromes. Measles is a major cause of lower respiratory tract infections and fatality in tropical countries.

Diagnosis—nasopharyngeal aspirates, washes and swabs are superior to throat and nose swabs for diagnosis, with virus detected by culture or detection of antigen or nucleic acid (e.g. PCR-based methods). New respiratory viruses continue to be discovered, but some acute respiratory infections have no identifiable aetiology, and some patients have multiple respiratory viruses detectable in the respiratory tract in association with their disease—whether these have a synergistic role in pathogenesis remains unclear.

Particular respiratory tract viruses

Influenza—types A and B are clinically important causes of human disease; the viral envelope contains two glycoproteins, haemagglutinin (H) and neuraminidase (N), which are critical in host immunity and used to designate viral subtype, e.g. H1N1. Potential to cause pandemics makes influenza type A a unique challenge for global public health. Typically causes an illness associated with fever, chills, headache, sore throat, coryza, nonproductive cough, myalgia, and sometimes prostration. Can cause pneumonia directly or by secondary bacterial infections. Oseltamivir and zanamivir result in a reduction of 1 to 2 days in the time to alleviation of symptoms when administered within the first 48 h of illness, but even later commencement of therapy may still confer clinical benefit in severe influenza illness. Can be prevented by influenza vaccine, which contains antigens from the two subtypes of human influenza A (H3N2 and H1N1) and B viruses, but the composition of the vaccine must be updated on an annual basis to keep abreast of change in the surface antigens of the virus, and annual reimmunization is required. Synergic interaction with Streptococcus pneumoniae enhances pathogenesis, and pneumococcal conjugate vaccine reduces hospitalization associated with respiratory viruses.

Respiratory syncytial virus (RSV)—a major cause of bronchiolitis and pneumonia in infants. Infection in adults is often asymptomatic, but during the RSV season (winter months in temperate regions) it is an important cause of lower respiratory tract infection in adults, particularly elderly people. May be lethal (as can other respiratory viruses) in patients immunocompromised following organ or blood and marrow transplants (but is not a significant problem in patients with AIDS).

Severe acute respiratory syndrome (SARS)—this novel coronavirus of animals adapted to efficient human transmission and spread worldwide, causing a global outbreak in 2003 of an illness characterized by lower respiratory tract manifestations, severe respiratory failure, and death in about 10% of cases. Public health interventions interrupted viral transmission and it is no longer transmitting within humans, but the precursor virus remains in the animal reservoir (bats, Rhinolophus spp.) and may readapt to cause human disease in the future.

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