Download Non-Influenza Respiratory Viruses

Infectious diseases Board Review Manual
Statement of
Editorial Purpose
The Hospital Physician Infectious Diseases Board
Review Manual is a study guide for fellows and
practicing physicians preparing for board exam­
inations in infectious diseases. Each manual
reviews a topic essential to current practice
in the subspecialty of infectious diseases.
Non-Influenza Respiratory
Viruses
Editor:
Varsha Moudgal, MD
Infectious Diseases Fellowship Program Director, St. Joseph Mercy
Hospital, Ann Arbor, MI; and Assistant Professor of Medicine, Wayne
State University School of Medicine, Detroit, MI
Contributors:
Bryan D. Hess, MD
PUBLISHING STAFF
PRESIDENT, Group PUBLISHER
Bruce M. White
Senior EDITOR
Robert Litchkofski
Division of Infectious Diseases and Environmental Medicine,
Department of Medicine, Jefferson Medical College, Thomas Jefferson
University, Philadelphia, PA
Joseph A. DeSimone, Jr., MD
Division of Infectious Diseases and Environmental Medicine,
Department of Medicine, Jefferson Medical College, Thomas Jefferson
University, Philadelphia, PA
executive vice president
Barbara T. White
executive director
of operations
Jean M. Gaul
Table of Contents
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Respiratory Syncytial Virus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Human Metapneumovirus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Parainfluenza Viruses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
NOTE FROM THE PUBLISHER:
This publication has been developed with­
out involvement of or review by the Amer­
ican Board of Internal Medicine.
Adenovirus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Copyright 2012 by Turner White Communications Inc., Wayne, PA. All rights reserved.
www.hpboardreview.com
Infectious Diseases Volume 13, Part 1 Infectious Diseases Board Review Manual
Non-Influenza Respiratory Viruses
Bryan D. Hess, MD, and Joseph A. DeSimone, Jr., MD
Introduction
Viral and bacterial infections of the respiratory
tract contribute significantly to worldwide morbidity
and mortality. This board review manual will discuss
infections with respiratory syncytial virus, human metapneumovirus, parainfluenza virus, and adenovirus in
immunocompetent hosts.
Respiratory Syncytial Virus
The pathogen now known as respiratory syncytial virus
(RSV) was originally isolated by Morris and colleagues
in 1956 from chimpanzees with respiratory illness and
was named chimpanzee coryza agent (CCA).1 Isolates of
CCA were later recovered from humans with respiratory
illness, and CCA antibodies were found present in most
school-aged children.2 The virus was renamed respiratory
syncytial virus, and has since been identified as the major
etiologic agent in lower respiratory tract disease among
infants and young children worldwide.3,4 RSV infection
induces incomplete immunity, and symptomatic reinfection is common in patients of all ages.5
Virology
RSV belongs to the family Paramyxoviridae, subfamily Pneumovirinae, and genus Pneumovirus.6 Like all
members of the paramyxovirus family, RSV is an enveloped virus with a genome consisting of nonsegmented,
single-stranded, negative-sense RNA.6 RSV is classified
into 2 subgroups (A and B) based on antigenic variations
observed in transmembrane surface proteins.7
Pathogenesis
Transmission of RSV occurs via direct person-toperson contact and via exposure to contaminated respiratory droplets and fomites.5,8,9 Common portals of entry include the mucosa of the nose and eyes.10 Once infected,
the incubation period for RSV illness is 2 to 8 days.
RSV demonstrates tropism for respiratory epithelial
cells. Proliferation of RSV in the lower respiratory tract
leads to necrosis of the bronchiole epithelium. Hyper-
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inflation may result from obstruction of the small airways by sloughed epithelial cells and increased mucus
secretion. These events manifest clinically as increased
lung volume and increased expiratory resistance.6
Epidemiology
RSV is a ubiquitous virus that produces yearly seasonal outbreaks of respiratory illness throughout the
world.5,11,12 In temperate climates, outbreaks of RSV
occur in the winter and spring months. RSV activity
may be prolonged in warmer climates, with low level
activity occurring throughout the year.13 In the United
States, incidence rates of RSV-related illness are typically highest in January and February (Figure 1).12 Geographic and climatic factors, in addition to population
behavior and preexisting immunity, are thought to play
a role in the variable epidemiologic patterns of RSV
outbreaks.9,13–16
Co-circulation of RSV groups and subtypes is observed during RSV outbreaks.17–19 Dominant strains vary
yearly and geographically, suggesting that preexisting
immunity within the affected population exerts selective
pressure on the circulating viral strains. Data regarding
the correlation between circulating subtypes and disease severity has thus far been inconclusive.5,20,21
Infants and Young Children
RSV is the most common cause of lower respiratory
tract disease in infants and young children worldwide.3,4
Serological studies have demonstrated RSV exposure in
nearly 80% of children by the age of 2 years and virtually all children by 5 years of age.22,23 In the United States,
bronchiolitis is the most frequent reason for hospitalization of infants and young children, with 75,000 to
125,000 admissions occurring each year.3 RSV infection
is thought to be responsible for 50% to 80% of these
cases. Risk factors for hospitalization include young
age (<3 months of life), preterm gestation, underlying cardiopulmonary conditions, and compromised
immunity.6 Of all hospitalizations for RSV, more than
half occur in children less than 6 months of age and as
many as 80% occur in children younger than 1 year.3
A major proportion of the health care burden attributable to RSV resides in outpatient care.4 While data
Infectious Diseases Volume 13, Part 1