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Chapter 17 : Respiratory Viruses
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Acute respiratory tract illnesses are the most common health conditions affecting humans. Six "classic" respiratory viruses have been known for decades: respiratory syncytial virus (RSV), influenza virus, human parainfluenza virus, rhinovirus, adenovirus, and the coronaviruses (CoVs) OC43 and 229E. The seasonality of most newly described respiratory viruses remains mostly investigational. Classification of viruses that primarily infect the respiratory tract are provided in this chapter. Relative importance of major respiratory viruses in upper and lower respiratory tract diseases are provided in this chapter. Vaccination and antiviral therapy are highly effective at limiting the spread of influenza virus, but these approaches are not available for other respiratory viruses. The major differences between human metapneumovirus (HMPV) and RSV are gene order and the absence of NS1 and NS2 genes in HMPV. The potential for coinfections involving HMPV and other respiratory viruses, especially RSV, is high given their overlap in seasonality. It begins with a profuse watery nasal discharge which may become mucopurulent and viscous. The number of real and potential respiratory viruses has increased considerably, and improved laboratory methods to detect them now abound.
Temporal patterns of four common respiratory viruses detected over a 6-year period by The Children’s Hospital Virology Laboratory, Denver, CO. Numbers of detections are as indicated, except during a large outbreak of influenza A in November and December of 2003 when approximately 950 and 400 specimens were positive for influenza A, respectively.
Transmission patterns of influenza A virus. The current hypothesis is that wild aquatic birds are the major reservoir of most types of influenza A, some of which can be transmitted to domestic birds and mammals. The double-headed arrow indicates that transmission of influenza A virus between pigs and humans has been demonstrated. Transmission of influenza A from birds to felines and dogs is not depicted. (Reprinted from Trampuz et al., 2004, with permission of the publisher.)