Chp
21 Bacterial & Vial Infections of the Respiratory System
A. Structure & Function - 2 Regions:
1. Upper Respiratory System
a. nasal
cavity
- incoming air is filtered by mucus (which
traps dust particles) and cilia of columnar epithelial cells (which move the particles to
the throat for elimination) – called the mucociliary
defense.
b. pharynx
- extends from the internal nares and extends partway down the neck, where it opens into
the esophagus (food tube) and the larynx; 3 regions of the pharynx: nasopharynx (uppermost portion; contains 2
internal nares & 2 openings that lead into the Eustachian tubes to equalize ear, nose,
& throat air pressure),
c. oropharynx
(middle portion; serves as a common passageway for air, food, drink), laryngopharynx
(lowest portion; just above the esophagus and larynx).
d. associated
structures:
1.) sinuses - air-filled cavities; one fxn.: produce mucus.
2.) tonsils
- nodules of lymphatic tissue that form a ring at the junction of the oral cavity &
oropharynx & at the junction of the nasal cavity and nasopharynx; the single adenoid
tonsil is embedded in the posterior wall of the nasopharynx.
3.) epiglottis
- large , leaf-shaped piece of cartilage lying on top of larynx; during swallowing the
larynx elevates, causing the epiglottis to fall on the glottis (opening into larynx) like a lid, closing
it off - this prevents food from entering the windpipe (trachea).
2. Lower Respiratory System
a. larynx
(voice box) - mucous membranes are composed of ciliated columnar epithelial cells.
b. trachea
(windpipe) - air passageway extending from the larynx; it divides into right and left
primary bronchi; mucous membranes are composed of ciliated columnar epithelial cells;
windpipe is supported by hyaline cartilage rings.
c. bronchi
- the trachea divides in to a right primary
bronchus (goes to right lung) and a left
primary bronchus (goes to left lung); bronchi are similar in structure to the trachea;
upon entering each lung the primary bronchi divide to form smaller bronchi - the secondary bronchi; secondary bronchi continue to
branch into smaller bronchi, called tertiary
bronchi, that then divide into bronchioles,
which divide into even smaller terminal bronchioles.
As the tubes get smaller, several structural changes occur:
¨ Cartilage
rings are replaced by cartilage plates and then the cartilage disappears all together.
¨ The
mucous membrane changes from ciliated columnar epithelium to cuboidal epithelium (any
debris reaching these smaller tubes must now be removed by white blood cells).
¨ As
the cartilage decreases the amount of smooth muscle increases during asthma attacks the
muscles go into spasm and because there is no supporting cartilage the spasms close off
the air passageways - asthma medication such as albuterol targets this smooth muscle
tissue).
d. lungs
- lobes contain lobules (small compartments in
the lungs); each lobule contains a lymphatic vessel, an arteriole, a venule, and a branch
from a terminal bronchiole; terminal bronchioles
subdivide into microscopic branches called
respiratory bronchioles, which subbdivide into several alveolar ducts; around each alveolar duct are alveolar sacs containing alveoli (cup-shaped projections lined with
epithelium); the exchange of respiratory gases between the lungs and blood takes place by
diffusion across the alveolar and capillary walls; the lungs are surrounded by a membrane
called the pleura.
1. Defenses
a. mucociliary
defenses in upper respiratory system, larynx, trachea, & bronchi (cilia on that
columnar epithelial cells whips up mucous.
b. macrophages
in the bronchioles & alveoli.
c. IgA (antibody) protects mucous
membranes.
2. Normal
Flora - includes species of streptococci, lactobacilli, & some Gram negatives in the
upper respiratory system; the lower respiratory system (as well as the sinuses &
middle ear) is normally sterile.
1. Rhinitis
- nasal inflammation; most common of all respiratory syndromes.
2. Adenoiditis
- infection of adenoid tonsil
3. Pharyngitis
- infection of the throat; called tonsillitis
if tonsils are primarily infected; symptoms include sore throat, sometimes fever, throat
may be covered by a milky white exudate, ulcers, blisters, or even a grayish membrane.
4. Sinusitis
- sinuses fill with fluid & become infected.
6. Epiglottitis
- infection of the epiglottis; can cause the epiglottis to swell to many times its normal
size; can cut off respiration and cause sudden death; on rare occasions laryngitis
(infection of the larynx) & laryngotracheobronchitis
(croup - produces a barking cough) may also
cause this to occur; a severe airway narrowing near the epiglottis or the larynx causes stridor (whistling sound heard as the person
breathes in).
7. Bronchitis
- infection of the bronchi; produces a thick, infected mucous; cough brings up infected
phlegm; fever is another symptom; complete obstruction does not occur because the bronchi
are so numerous.
8. Bronchiolitis
- infection of the bronchioles; inflammation narrows these tiny collapsible airways; air
can enter, but has difficulty getting out; clinical signs include wheezing (musical noise heard during expiration)
& trachyapnea (rapid breathing).
9. Pneumonia
- infection of the lungs, with fluid & microbes replacing the air that normally fills
the alveoli; normal gas exchange cannot take place; clinical signs include fever,
trachyapnea, labored breathing, & a cough that may produce infected secretions; if
pneumonia involves the pleura, it causes pleurisy,
associated with painful breathing; caused by bacteria, viruses, and fungi.
A. Bacterial
Causes of URI's (Bacteria are the most
virulent of the u.r. pathogens, but the great thing is that they can be treated with
antibiotics!)
1. Haemophilus
influenzae
a. General
¨ G(-)
rod
¨ needs
a growth factor present in human red blood cells - hence the name Haemophilus ("blood
loving")
¨ once
thought to cause influenza - IT DOES NOT CAUSE INFLUENZA (“the flu”)!!
¨ major
cause of virulence is the production of a capsule.
b. URI's:
1.) epiglottitis
- caused by H. influenzae type B (encapsulated) – adults produce
Ab's, but young children are at risk; ampicillin not effective due to plasmid-borne
antibiotic resistance; conjugate vaccine (Hib) now available; babies are routinely
immunized against this pathogen.
2.) sinusitis
- caused by H. influenzae (nonencapsulated) strains
3.) otitis
media
(middle ear infection) - caused by H. influenzae (nonencapsulated)
strains.
c. H. influenzae type
B (encapsulated) also causes:
1.) meningitis
- infection of membranes covering the brain & spinal cord; before the vaccine this
bacterium was the leading cause of meningitis and mental retardation in children.
2.) cellulitis
- infection of skin & subcutaneous tissues.
3.) conjunctivitis
(pink eye)
2. Streptococcus
pyogenes
a. General:
¨ G(+)
cocci
¨ pyogenes means "pus forming"
¨ do
not produce the enzyme catalase (distinguishes them from the Staphs)
¨ medically
important strains are classified by their hemolytic & serological properties [see lab manual for beta vs. alpha hemolysis; S. pyogenes is usually beta hemolytic - clear zones
of hemolysis]
b. URI's:
1.) pharyngitis
(strep throat) - transmitted by respiratory droplets or contaminated food/drink; clinical
signs: severe sore throat, fever, chills,
headache, inflamed pharynx, tender lymph nodes in neck; whitish exudate on tonsils;
diagnosis: latex agglutination kit that
detects Ag in throat swab.
c. Complications of strep throat:
1.) scarlet
fever
- some strains produce an erythrogenic exotoxin that causes scarlet fever; the toxin kills
cells and causes intense inflammation; was once a life-threatening illness; today's cases
are mild (due to a decrease in virulence).
2.) septicemia
-
bacteria spread to into the blood stream
3.) rheumatic
fever
- occurs after the infection is over (postinfection
complication); causes inflammation of joints, skin, brain, heart valves (endocarditis); leading cause of heart disease
among children in developing countries; bacteria have an Ag similar to that on heart cells
– wbc’s become sensitized to the bacterial Ag, then attack the heart cells;
disease can be prevented if strep throat is treated with penicillin within first 10 days;
r.f. patients should receive a monthly penicillin injection - they are in danger if they
contact another strep infection.
d. Other diseases caused by Streptococci:
1.) Impetigo
(pyoderma) –
highly contagious; occurs almost exclusively in children; usually different strain than
those that cause strep throat; easily treated with penicillin; usually heals without
scarring, but pigment can be permanently lost; also caused by staphylococci.
3. Corynebacterium
diphtheriae
a. General:
¨ G(+)
irregular rod
¨ produce
an exotoxin; gene for exotoxin is carried by a temperate bacteriophage, so only strains infected by this
virus can produce toxin & cause diphtheria; toxin interferes with protein synthesis in
eukaryotic cells.
b. Diphtheria
¨ transmission: respiratory droplets; bacteria is noninvasive, but
deeper tissues are affected because they absorb the toxin
¨ clinical
signs: infected throat swells & becomes
covered by a tough, grayish pseudomembrane
composed of dead human cells & microbes [membranous pharyngitis]; swollen tissue &
pseudomembrane can obstruct airway, leading to death by suffocation; fatal complications
can also result if toxin enters the blood stream and damages other organs; treatment: horse antitoxin (serum sickness is a potential
risk)
¨ prevention: toxoid vaccine - produced by treating toxin with
formaldehyde - part of DPT (diphtheria-pertussis-tetanus) series given to infants;
immunization does not confer lifelong immunity - adults should have a booster every 10
years!
4. Bacterial causes of the common
cold: Mycoplasma
pneumoniae, Coxiella burnetii.
Remember that most
colds are viral.
B. Viral
Causes of URI's - more common & less serious than bacterial infections; treatment is a
challenge (antibiotics are worthless). (See
Chapter 10 on these groups of viruses)
1. Rhinoviruses
a. General
¨ RNA
viruses
¨ named
for portal of entry - rhino means "nose"
¨ primary
cause of commn cold - causes 1/4 to 1/2 of colds.
¨ about
100 different serotypes (have different antigens in capsids), with new types continuing to
be identified.
b. Common
Cold
- clinical signs: sneezing, rhinorrhea (excess nasal mucous), nasal
congestion, sore throat, fever, headache; malaise (feeling of general discomfort) due to
interferons produced to combat the infection; cold typically lasts 1 week; transmission
mainly by direct contact (hand to hand) or fomites; also by respiratory droplets;
treatment: none - recovery depends on
individual's immune system - antibiotics are useless; over-the-counter medications only
help alleviate symptoms.
2. Coronaviruses - also cause the common cold.
a. General
¨ named
for prominent spikes on their outer surface
¨ difficult
to isolate in cell culture
¨ cause
10-15% of colds in adults (also cause pneumonia & intestinal infections).
3. Other
viral causes of the common cold: coxsackieviruses,
echoviruses, adenoviruses, myxoviruses.
1. Streptococcus
pneumoniae [pneumococcus]
a. General:
¨
G(+),
lancet-shaped diplococci (paired diplococci with pointed ends)
¨
do
not produce catalase; optochin sensitive; alpha hemolysis
¨
part
of normal flora of 10% of population
¨
capsule
is critical factor in virulence
¨
causes
90% of acute bacterial pneumonias
b. Pneumococcal Pneumonia
1.) transmission
- respiratory droplets
2.) clinical
syndrome: bacteria in the lung trigger an
intense inflammatory response; leaky capillaries allow fluid, blood cells, & serum
proteins to flow into the alveoli, filling them; the affected region becomes consolidated,
giving the impression of a solid organ when tapped, listened to, or penetrated by x-rays;
difficult & labored breathing occur; sputum is bright with blood; 30% of untreated
patients die - suffer from unrelenting fever & worsening respiratory problems; pneumococcal sepsis (bacteria enter the
bloodstream) can occur - particularly in patients with no spleen - spleen filters out
bacteria for macrophages to engulf and process Ag (Ag
presentation in antibody-mediated response).
4.) vaccine: Pneumovax
- polyvalent (multiple-Ag) vaccine.
5.) bacteria
that cause the same clinical syndrome: Haemophilus influenzae, Klebsiella pneumoniae,
Staphylococcus aureus, Streptococcus pyogenes, E. coli .
2. Mycoplasma pneumoniae
a. General
¨
lack
a cell wall
¨
adhere
to epithelial cells; do not invade deeper tissues
¨
grow
slowly in lab
¨
grows
in trachea; transmitted in respiratory droplets
b. Mycoplasma
Pneumonia (Primary Atypical Pneumonia or
"Walking Pneumonia")
1.) clinical
syndromes: occurs most frequently in
school-age children & teens; comes on gradually; mild; causes headache, low-grade
fever, persistent dry cough; shows a patchy pattern in chest x-rays rather than dense
consolidation of an entire lobe; rarely fatal; viruses, chlamydiae, & rickettsiae
cause similar atypical pneumonias.
2.) treatment: tetracycline; erythromycin for pregnant women
& young children; not sensitive to penicillins & cephalosporins because they lack
a cell wall.
3. Chlamydia psittaci
a. General
¨ obligate
intracellular parasites; can only be cultured in lab in chick embryos; therefore,
infections are usually diagnosed serologically.
¨ psittaci means "parrot"
b. Ornithosis,
Psittacosis, or Parrot Fever
1.) transmission
- microbe commonly infects all types of birds; usually does not produce illness in bird;
disease spreads when infected bird become stressed and microbe is excreted in bird's
droppings; humans inhale microbe from droppings; occupational hazard for bird handlers or
those working in poultry industry.
2.) clinical
syndrome - fever, headache, chills, cough; can progress to persistent high fever, mental
confusion, & marked shortness of breath.
3.) prevention
- antibiotic supplements in feed & antibiotic treatment of imported birds have
prevented many infections.
a. General
¨ rickettsia
- life cycle requires both insect (tick) & vertebrate hosts; obligate intracellular
parasite
¨ "Q"
stands for query, as etiologic agent was unknown.
¨ Another
species causes trachoma, a blinding conjunctivitis.
b. Q Fever
1.) transmission
- humans become infected by inhaling the microbe from infected animal placentas, feces,
amniotic fluid, or milk (they can survive the pasteurization process).
2.) clinical
syndrome: atypical pneumonia; can't be
distinguished clinically from mycoplasmal pneumonia or parrot fever; rare disease; rarely
causes death.
5. Legionella pneumophila
a. General
¨ In
1976, 183 American Legion conventioneers in Philadelphia became ill with a mysterious form
of pneumonia.
¨ this
flagellated microbe can be seen only by means of special stains, such as
silver-impregnation stains or IFA.
¨ can
live inside macrophages; multiply as an intracellular pathogen.
b. Legionellosis or Legionnaires' disease
1.) transmission
- lives in natural & artificial water supplies; survives heat & chlorination;
infections occur when waterborne microbes become aerosolizes & are inhaled
(water-cooled air conditioning systems).
2.) clinical
syndrome - minor symptoms in most; some develop a virulent pneumonia - sudden onset,
weakness, headache, high fever, cough, shaking chills; x-rays show consolidation of an
entire lobe; smokers & alcoholics are particularly susceptible.
3.) treatment
- resistant to penicillin & cephalosporins; early diagnosis is critical in order to
treat with erythromycin.
6. Bordetella pertussis
a. General
·
G(-)
coccobacillus
·
produces
exotoxins
·
pertussis
means "intensive cough"
b. Pertussis
(Whooping Cough)
1.) transmission
- respiratory droplets; highly contagious
2.) clinical
syndrome - uncontrollable fits of coughing (paroxysms)
3.) treatment
- by the time diagnosis occurs, the toxin has caused considerable damage, so antibiotic
treatment does little to shorten the illness; supportive nursing care is the only
treatment.
4.) prevention
- infants are protected by the DPT immunization series; vaccine has side effects (fever,
convulsions in some); an acellular vaccine genetically engineered vaccine is being
developed.
7. Mycobacterium tuberculosis
a. General
·
rod-shaped
obligate aerobe; id. by Robert Koch
·
waxy
cell capsule contains mycolic acids; called "acid fast;" require special
staining techniques; waxy capsule allows microbe to survive prolonged drying and resists
digestion by lysozymes inside a phagocyte; can remain viable for as long as 8 months upon
entering the air when a patient coughs.
·
other
species also cause tuberculosis.
b. Tuberculosis
- leading killer among infectious diseases today; can also affect the lymphatic, the
genitourinary, the skeletal, & the nervous systems.
1.) transmission - respiratory
droplets
2.) clinical syndrome:
a.) primary
infection
- microbes enter the lungs & are phagocytized by alveolar macrophages, but are not
killed; several weeks later, T cells are activated, eliciting a cell mediated immune
response & tuberculin hypersensitivity (Type IV, delayed); cellular immunity helps
control the infection - hypersensitivity causes most of the tissue damage associated with
severe cases; the bacteria are isolated within nodules called tubercules or granulomas (dense collections of activated
macrophages & lymphocytes); if host cells in the center of a tubercle die, the dead
tissue looks dry & crumbly, like cheese (called caseation
necrosis - "cheeselike death"); bacteria can persist in these granulomas for
many years; progressive primary infection can occur - cellular immunity fails to control
the microbes and they spread to other parts of the body; miliary tuberculosis is a life threatening form
of the disease - infection sites are so numerous, they look like seeds of millet (grain)
scattered throughout the body.
3.) prevention
1.) BCG
vaccine
- Bacilllus Calmette-Guerin - made from attenuated M.
bovis; not entirely reliable; not widely used in U.S., but is used in other parts of
the world.
2.) Skin testing
4.) treatment
- people who have a positive skin test but do not have active tuberculosis are treated
with a single drug (ex. isoniazid) for 1 yr. (prevents reactivation infection); people
with active infections receive multiple drug therapy for 2 years.
Important: The number of cases in the U.S. is on the rise. New drug-resistant strains have been identified; have emerged in patients who did not finish their full course of medication and are lost to medical follow-up.
1. Influenza virus
a. General
·
orthomyxovirus
family, enveloped virus
·
composed
of 8 separate pieces of RNA; this and its ability to infect an already infected cell
enables the virus to undergo genetic recombination (antigenic shift); this contributes to
the virus's genetic variability & potential to cause epidemics.
·
different
strains: A (most severe; responsible for
pandemics), B (common cause In children), & C
b. Influenza (Flu)
1.) transmission
- animal reservoirs are critical; Type a is widespread in birds, which transmit it to
pigs, who transmit it to humans (you may have heard of the "swine flu").
2.) clinical
syndrome - fever, headache, muscle aches, cough; tracheobronchitis; person becomes prone
to secondary bacterial infections because ciliated columnar epithelial cells are killed;
can also cause pneumonia.
3.) treatment
- antibiotics only prevent secondary bacterial infections; antiviral agent amantadine can
speed recovery if it is administered during the first 2 days of illness.
4.) prevention
- immunization (only 70% of those vaccinated are protected); changing Ag's required a new
vaccine every year.
2. Parainfluenza virus
a. General
·
paramyxovirus
family; RNA viruses; enveloped
·
some
cause common cold
b. Croup
1.) transmission
- respiratory droplets
2.) clinical
syndrome - laryngotracheobronchitis causes the airway to narrow at and below the vocal
cords; extremely severe cases can resemble epiglottitis, but the illness is usually milder
and more gradual in onset; common in toddlers; loud, barking cough; symptoms are worse at
night when mucous accumulates (take them outside in the cold - cold air constricts blood
vessels; cool mist humidifier thins mucous).
3.) treatment/prevention
- supportive nursing care; no immunization.
3. Respiratory Syncytial Virus (RSV)
a. General
·
paramyxovirus
·
infected
respiratory tissues develop syncytia (large, abnormal cells with multiple nuclei)
b. Bronchiolitis
- most common cause of fatal lower respiratory infection in young children/infants.
1.) transmission
- hand to hand; respiratory droplets; nosocomial infections.
2.) clinical
syndrome - infants under 6 mo. suffer the most; wheezing; rapid breathing.
3.) treatment/prevention - supportive
nursing care; no immunization.
4. Hantavirus
a. General
- arboviruses; named for Hantaan River in North Korea
b. Hantavirus
Pulmonary Syndrome - appeared mysteriously in the early 1990's in the 4 Corners area of
the American Southwest.
1.) transmission
- virus occurs in the long-tailed deer mouse; the mice shed the virus in their urine,
feces, & saliva, and people contract the disease by inhaling aerosolized viral
particles.
2.) clinical
syndrome - fever, muscle aches, respiratory distress; 70% of cases result in death within
5-6 days; death caused by catastrophic lung failure; capillaries leak profusely &
fluid fills the air spaces.
(Portal of Entry is the Respiratory System,
but Usually Affect other Systems)
1. Mumps
- paramyxovirus; transmitted in saliva or respiratory secretions; enters a new host
through the respiratory system; infects salivary glands; swelling of glands results, along
with mild pain and sometimes fever; sometimes enters bloodstream and infects other
tissues; in adult males may infect the testes (inflammation called orchitis); in rare
cases it infects the inner ear, causing deafness; part of MMR (mumps, measles, rubella)
vaccine given at 15 mo.
2. Rubeola
Measles
(= Measles) - paramyxovirus; one of most communicable diseases known; virus is inhaled;
virus multiplies in respiratory tract, then spreads throughout the body, multiplying in
lymphoid tissue; virus fuses cell to one another - can be seen under the microscope;
symptoms: fever, cough , runny nose, conjunctivitis
("pink eye"), Koplik spots appear
around mouth; rash appear first on face and gradually spreads downward to cover the entire
body; complications such as ear infections, pneumonia, & encephalitis can occur; part
of MMR vaccine given at 15 months.
3. Rubella
measles (German Measles) – paramyxovirus; virus is
inhaled; incubation period is 2 weeks; symptoms: mild
fever, rash that lasts less than 3 days, swollen lymph nodes; complications are rare; not
as communicable as measles or chickenpox; infection during first 3 months of pregnancy can
cause a miscarriage or birth defects; part of MMR vaccine given at 15 months.
4. Varicella
Zoster (Chicken pox & Shingles)
- like herpes, this virus establishes a latent infection in nerve cells that can be
reactivated later; people infected for the first time develop a generalized infection
called varicella or chickenpox, that produces blisters all over the body; recovery is
complete, but the virus remains latent in neurons; adults who come down with chickenpox
can contract a life threatening viral pneumonia; chickenpox during pregnancy is dangerous;
reactivation of a latent varicellla zoster infection is called shingles; it is usually
brief, but can be painful; passive immunization with varicella zoster immune globulin
(VZIG) greatly decreases the severity of chickenpox if administered within 3 days of
exposure; an active vaccine has been approved in the U.S. & is currently being
administered.
5. Smallpox
(Variola virus)
- virus is inhaled; less communicable than measles, but very hardy; disease was eradicated
in 1979; a closely related poxvirus, vaccinia, is used for smallpox immunization; severity
of disease depends on strain; produces a high fever and a severe blistering rash, killing
about half of its victims.
6. Infectious
Mononucleosis ("Kissing Disease")
- caused by Epstein-Barr Virus (EBV); associated with lymphatic system; virus establishes
a latent infection in B cells symptoms: fever, fatigue, sore throat, swollen lymph nodes,
enlarged spleen (spleenomegaly - appears 1-2
mo. after infection); in most patients, the illness lasts 4-6 weeks; EBV is one of the few
viruses proved to be oncogenic (Burkitt's lymphoma, nasopharyngeal carcinoma, B cell
lymphoma).