Infectious Diseases Affecting the Respiratory Tract

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 infectionsare commonillnesses inearly 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 theformation ofinclusion 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 tuberculinreaction in theMantoux test canbe used for earlydetection of TBexposure

•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 inimmunization

•Infectious bronchitis is an inflammation of the bronchi

•Bronchitis produces excessivemucus and a narrowingof 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 aprimary or secondary infection in

people with impaired pulmonaryfunction

“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 alsocauses Pontiac fever,an influenza-likeinfection

Some Rickettsiae and Chlamydiae Also Cause Pneumonia

•Coxiella burnetii causes Q fever, a prevalent disease of livestock

•Humans can acquirethe disease byconsumingcontaminated rawor 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-to-Person Contact

•SARS is an emerging infectious disease of the family Coronaviridae

•It is spread by contactwith an infected personor an object upon which

they have coughed orsneezed

•Bats may be the naturalhost 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