Chapter 20
Infectious Diseases Affecting the Respiratory Tract
20.1 Structure and Function of the Respiratory System
• Upper respiratory defenses limit microbe colonization of the lower respiratory
tract
• Microbial colonization is limited to the upper respiratory tract
• Mucociliary clearance involves the entrapment of microbes and
particulates larger than 2 µm in a layer of mucus
20.2 Bacterial Diseases Affecting the Upper Respiratory Tract
• Pharyngitis is an inflammation of the throat
• S. pyogenes causes streptococcal pharyngitis (strep throat)
• It enters the upper respiratory tract through respiratory droplets
• Some patients with strep throat may develop scarlet fever, exhibiting a
rash caused by erythrogenic exotoxins
• Strep throat and scarlet fever can be treated by antibiotics
• Rheumatic fever is a serious complication affecting the joints and heart
• It causes permanent heart damage called rheumatic heart disease
• Acute glomerulonephritus is a rare inflammatory response to M proteins
• It may lead to renal damage
Diphtheria Is a Life-Threatening Illness
• Diphtheria is a local infection of the throat caused by Corynebacterium
diphtheriae
• C. diphtheriae bacilli remain in clumps after multiplying, forming a palisade layer
• Diphtheria is acquired by respiratory droplet transmission
• The bacteria produce an exotoxin that inhibits translation
• This results in the accumulation of a pseudomembrane on the tonsils or
pharynx
• Treatment requires antibiotics and antitoxins
• Injection of diphtheria toxoid is used for vaccination
• There are usually less than a dozen confirmed cases in the United States each year
• The epiglottis is subject to infection, especially in children
• Swelling of the epiglottis can block the trachea
• The nose is the most commonly infected part of the upper
respiratory tract
• Sinusitis
• Ear infections are common illnesses in early childhood
20.3 Viral Infections of the Upper Respiratory Tract
• Rhinovirus Infectious Produce Inflammation in the Upper Respiratory Tract
• Rhinoviruses belong to the Picornaviridae family
• They are transmitted by airborne respiratory droplets or contact with
contaminated objects
• Rhinoviruses are responsible for many cases of the common cold
• More than 100 different rhinovirus strains can cause common
colds
• Researchers are developing drugs for treating rhinovirus infections
• Adenovirus Infections Also Produce Symptoms Typical of a Common Cold
•
•
Adenoviruses belong to family Adenoviridae
They induce the formation of inclusion bodies
in host tissues
• Adenoviruses are transmitted through respiratory droplets
• Infection can cause
• acute febrile pharyngitis
• pharyngoconjuntival fever
• acute respiratory disease
• Any of these can progress to viral pneumonia
20.4 Diseases of the Lower
Respiratory Tract
• Pertussis (Whooping Cough) is Highly Contagious
• Bordatella pertussis is spread by respiratory droplet transmission
• Toxin paralyzes ciliated cells in the respiratory tract
• Patients experience multiple paroxysms of coughs, followed by an inhalation of
breath that sounds like a “whoop”
• Erythromycin reduces the duration and severity of illness
• The newer vaccine contains B. pertussis chemical extracts rather than killed cells
• The number of cases in the United States has been rising since 1981
Tuberculosis Is a Major Cause of Death Worldwide
• 2 million people die of TB every year,
globally
• Mycobacterium tuberculosis enters the respiratory tract in small aerosolized
droplets
• About 90% of people who carry latent tuberculosis will never develop an active
infection
• They may never even know they are infected
• Clinical TB develops within 3 months and can be transmitted to others
• Sputum coughed from the lower respiratory tract may contain blood
• Macrophages accumulate in the lung
• They form a tubercle that harbors M. tuberculosis
• If a tubercle breaks apart, bacteria spread throughout the body
• Miliary tuberculosis is the development of active tubercles throughout the
body
• The tuberculin reaction in the Mantoux test can be used for early detection
of TB exposure
• Multidrug-resistance Mycobacterium tuberculosis is affecting which
antibiotics are used to treat TB
• TB is a particularly big problem for AIDS patients
• Attenuated M. bovis is used in immunization
• Infectious bronchitis is an inflammation of the bronchi
• Bronchitis produces excessive mucus and a narrowing of the bronchi “Typical”
Pneumonia Can Be Caused by Several Bacteria
• 80% of “typical” pneumonia cases are caused by Streptococcus pneumoniae
• It is acquired through aerosolized droplets or contact
•
Pneumococcal pneumonia can involve
• an entire lung lobe (lobar pneumonia)
• both lungs (double pneumonia)
• or patches in the respiratory passageways (bronchopneumonia)
• Haemophilus influenzae can cause
• “typical” pneumonia
• otitis media sinusitis
• Staphylococcus aureus is a common hospital-acquired form of pneumonia
• It may result in necrotizing pneumonia
• Klebsiella pneumoniae can be a primary or secondary infection in
people with impaired pulmonary function
“Atypical” Pneumonia Can Be Caused by a Diverse Group of Bacterial Species
• Mycoplasma pneumoniae causes primary atypical pneumonia, often called
walking pneumonia
• M. pneumoniae has no sensitivity to penicillin because it has no cell wall
• The cold agglutinin screening test (CAST) is used to assist diagnosis
Legionella pneumophila causes Legionnaires’ disease
• It lives where water collects and becomes airborne in the wind (or
ventilation system)
• Disease develops within a week of inhalation of contaminated droplets
• Necrotizing pneumoniamay develop
• L. pneumophila also causes Pontiac fever, an influenza-like infection
Some Rickettsiae and Chlamydiae Also Cause Pneumonia
• Coxiella burnetii causes Q fever, a prevalent disease of livestock
• Humans can acquire the disease by consuming contaminated raw or improperly
pasteurized milk
• Chlamydia psittaci causes psittacosis (a.k.a. ornithosis)
• It is a zoonotic disease humans can catch from infected birds
• Chlamydia pneumoniae causes chlamydial pneumonia
• Inhalational anthrax is an occupational hazard
• Bacillus anthracis spores can be inhaled in contaminated dust
• Woolsorter’s disease
• Bioterrorism threat
20.5 Viral Infections of the Lower Respiratory Tract
• Influenza Is a Highly Communicable Acute Respiratory Infection
• It is transmitted by airborne respiratory droplets
• There have been at least 31 influenza pandemics since 1510
• The virion belongs to the Orthomyxoviridae family
• It contains two types of spikes
• Hemagglutin (H) helps the virion attach and penetrate host cells
• Neuraminidase (N) helps release virions from the host cell after
replication and assembly
• Influenza A strikes every year and causes most epidemics
• Influenza B also strikes every year but is less common than type A
•
•
Influenza C causes a mild respiratory illness but not epidemics
A new flu strain evolves every year, requiring development of a new
vaccine
• Complications such as pneumonia or secondary infections occur in
• Infants
• Elderly
• Immunocompromised people
• Guillain-Barré syndrome occurs when the body damages its own
peripheral nerve cells
• Reye syndrome often occurs in children who take aspirin to treat pain and
fever
• Paramyxovirus Infections Affect the Lower Respiratory Tract
• Respiratory syncytial (RS) disease is caused by the respiratory syncytial virus
(RSV)
• It commonly affects children under 1 year of age
• It infects the bronchials and alveoli of the lungs, causing cells to
fuse together into syncytia
• Parainfluenza infections are usually caused by human parainfluenza
viruses 1 and 3
• Infections are milder than influenza
• Human metapneumovirus (hMPV) are RSV-like viruses
• Symtoms are milder than RS disease
Other viruses also produce pneumonia
• Severe Acute Respiratory Syndrome (SARS) Spreads through Close Person-toPerson Contact
• SARS is an emerging infectious disease of the family Coronaviridae
• It is spread by contact with an infected person or an object upon which
they have coughed or sneezed
• Bats may be the natural host of the virus
• A moderate upper respiratory illness may develop into severe respiratory
illness and pneumonia
• All SARS patients should be isolated for at least 10 days after fever has
broken to prevent spread
• Hantavirus pulmonary syndrome (HPS) occurs in the southwestern United States
• It is caused by a strain of hantavirus named “Sin Nombre”
• The deer mouse is the host, shedding the virus in saliva, urine, and feces
• Humans become infected with hantavirus by inhaling dried, aerosolized urine or
feces
• Many patients suffer from
• headaches
• dizziness
• difficulty breathing
• low blood pressure
• Respiratory failure can occur as the lungs fill with fluid
20.6 Fungal Diseases Affecting the Lower Respiratory Tract
• Histoplasmosis Can Produce a Systemic Disease
• It is caused by Histoplasma capsulatum
• It is found in dry, dusty soil, chicken coops, and bat caves
• Most people suffer only mild influenza-like symptoms
• Blastomycosis Usually Is Acquired Via the Respiratory Route
• It is caused by Blastomyces dermatitidis
• It is associated with dusty soil and bird droppings
• Inhalation causes
• lung lesions
• persistent cough
• chest pains
• It can cause chronic pneumonia and may disseminate to other organs in
AIDS patients
• Coccidioidomycosis Can Become a Potentially Lethal Infection
• It is caused by Coccidioides immitis
• Inhalation of spores causing
• a dry, hacking cough
• chest pains
• high fever
• Rarely, infection disseminates to tissues such as meninges of the spinal
cord
• Opportunistic mycoses affect immunocompromised individuals
• Cryptococcosis usually occurs in immunocompromised individuals
• It is caused by Cryptococcus neoformans
• C. neoformans is found in urban soil and pigeon droppings
• Inhaled cells penetrate to the air sacs of lungs
• Cells can (rarely) pass into the bloodstream, infecting the brain and
meninges
Pneumocystis Pneumonia Can Cause a Lethal Pneumonia
• It is caused by Pneumocystis jiroveci
• It is a common infection in AIDS patients
• P. jiroveci has a complex life cycle in the alveoli
• It is usually transmitted through respiratory droplets
Other Fungi Also Cause Mycoses
• In aspergillosis, conidia enter the body and grow as a mycelium
• It is commonly caused by Aspergillus fumigatus
• Surgery may be necessary to remove an aspergilloma from the lungs
• Fungal toxins are called mycotoxins
• A. flavus and A. parasiticus produce carcinogenic aflatoxins
• Aflatoxins contaminate many agricultural products
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