Chapter 24: Microbial Diseases of the Respiratory System

Respiratory System Diseases

most common and most dangerous

The Upper Respiratory System

- Nose

- Pharynx (throat)

- Middle ear

- Eustachian tubes

The Lower Respiratory System

- Larynx

- Trachea

- Bronchial Tubes

- Alveoli

- Pleura

Normal Microbiota of Respiratory System

- Suppress pathogens by competitive inhibition in upper respiratory system.

- Lower respiratory system is sterile.

Upper Respiratory System Disease

"The upper respiratory system is the site for many types of infections from sub-clinical to chronic to lethal."

- Pharyngitis (inflammation of the pharynx)

- Laryngitis (inflammation of the larynx)

- Tonsillitis (inflammation of the tonsils)

- Sinusitis (inflammation of the sinuses)

- Epiglottitis: H. influenzae type b (only serious of upper respiratory system; closes trachea and you can't breathe; comes quickly)

Streptococcal Pharyngitis

- Also called strep throat

- Streptococcus pyogenes

- Resistant to phagocytosis

- Streptokinases lyse clots

- Streptolysins are cytotoxic

- Diagnosis by enzyme immunoassay (EIA) tests (antibody tests)

- DIsease is characterized by: local inflammation and fever, frequently involve tonsils and ears.

- Drug of choice is penicillin (b/c strep is gram + cocci)

Scarlet Fever

" When the Streptococcus progenies strain produces an erythrogenic toxin, the infection is called Scarlet Fever"

- Pinkish skin rash and spotted tongue

- Spread by droplet inhalation and usually associated with "Strep throat"

- Treat with Penicillin.

- You get strep and develop scarlet fever, or vice versa.

Diptheria

- Corynebacterium diphtheriae: Gram-pos rod

- Diptheria toxin produced by lysogenized C. diphtheriae (gets in throat)

- DTP vaccine (against toxin)

- Vaccine against toxin, not the bacteria

- Pathogenesis includes sore throat and fever followed by swelling of the neck and leather-like appearance of the tongue.

- Died from suffocation

- Antibiotics are penicillin in combination with antitoxins

Otitis Media

- Middle ear infection

- S. pneumoniae (35%)

- H. influenzae (20-30%)

- Incidence of S. pneumonia reduced by vaccine

- treat with amoxicillin

- replication and swelling in middle ear

Viral Diseases of the Upper Respiratory System (The Common Cold)

- The most common disease in humans

- Over 200 viruses that can cause a "cold": 50% are rhinoviruses (in nose) ; 15-20% are coronaviruses

- Accumulate immunities against cold viruses

- Symptoms include sneezing, runny nose, congestion (NO FEVER)

- Transmitted by hands and surfaces (formites)

- Very stable viruses outside human body.

Lower Respiratory System Diseases

- much more serious

- Bacteria, viruses, and fungi cause: Bronchitis (infection of bronchi) ; Bronchiolitis (infection of bronchioles) ; Pneumonia (any inflammation of respiratory tissue).

Pertussis (Whooping Cough)

- Bordetella pertussis (Gram-neg coccobacillus with capsule)

- Tracheal cytotoxin of cell wall damaged ciliated cells.

- Pertussis toxin

- Prevented by DTaP

- making a comeback

- Secretes toxin that kills ciliary escalade

- Throat accumulates mucous.

THREE STAGES:

Stage 1. Catarrhal stage, like common cold.

Stage 2. Paroxysmal stage - violent coughing sieges.

Stage 3. Convalescence stage (get this if not treated)

Tuberculosis

- Mycobacterium tuberculosis (Acid-fast rod; transmitted from human to human)

- Highly contagious - human-to-human

- TB is primarily a disease of the lungs

- Name comes from the formation of nodule in the lungs called tubercle.

- Detection is by a tuberculin skin test.

- Mantoux Test

- Positive reaction means current or previous infection. Followed by X-ray or CT exam, acid-fast staining of sputum, culturing of bacteria.

- In the U.S.: 20,000 new cases a yr (2,000 deaths/yr)

- 10-12 million ppl are infected in the US

- Worldwide: 1/3 of total population (3 million deaths/yr ; number of cases is rising 2% / yr)

- Treatment: Isoniazid, Rifampin, Pyrazinamide (Resistamt strains could also be treated with ethambutol and streptomycin). Treatment lasts for up to 6 months.

The Pathogenesis of Tuberculosis

1. Tubercle bacilli that reach the alveoli of the lung are ingested by macrophages, but often some survive. Infection is present, but no symptoms of disease.

2. Tubercle bacilli multiplying in macrophages case a hemolytic response that brings additional macrophages and other defensive cells to the area. These form a surrounding layer and, in turn, an early tubercle. Most of the surrounding macrophages are not successful in destroying bacteria but release enzymes and cytokines that cause lung damaging infection.

3. After a few weeks, disease symptoms appear as many of the macrophages die, releasing tubercle bacilli and forming a caseous center in the tubercle. The aerobic tubercle bacilli do not grow well in this location. However, many remain dormant (latent TB) and serve as a basis for later reactivation of the disease. The disease may be arrested at this stage, and the lesions become calcified.

4. In some individuals, disease symptoms appear as a mature tubercle is formed. The disease progresses as the caseous center enlarges in the process called liquefaction. The caseous center now enlarges and forms an air-filled tuberculous cavity in which the aerobic bacilli multiply outside the macrophages.

5. Liquefaction continues until the tubercle ruptures, allowing bacilli to spill into a bronchiole and thus be disseminated throughout the lungs and then to the circulatory and lymphatic systems.

Bacterial Pneumonias

- The term pneumonia applies to any pulmonary infection of which are bacteria.

- Most pneumonias are caused by Streptococcus pneumonae

- Other types caused by fungi or protozoa are called atypical pneumonias

- Pneumonias are named for the part of the LRS the infect such as bronchopneumonia, lobar pneumonia, or pleurisy.

Pneumococcal Pneumonia

- Streptococcus pneumoniae (Gram-pos encopsulated diplococci - pathogenic!)

- Symptoms: Infected alveoli of lung fill with fluids; interferes with oxygen uptake.

- Treatment: Penicillin, fluoroquinolones

- Prevention: Pneumococcal vaccine

- If untreated = suffocation from fluid in lungs

Haemophilus influenzae Pneumonia

- Gram-neg coccobacillus

- Opportunistic

- Predisposing factors: Alcoholism, poor nutrition, cancer, or diabetes (compromised people)

- Symptoms: Resemble those of pneumococcal pneumonia

- Treatment: Cephalosporins

Mycoplasmal Pneumonia

- Primary atypical pneumonia; walking pneumonia

- Mycoplasma pneumoniae (Pleomorphic, wall-less bacteria (no cell wall))

- Common in children and young adults

- Symptoms: Mild but persistent respiratory symptoms; low fever, cough, headache

- Treatment: Tetracyclines

- Difficult to diagnose b/c gram-stain is negative.

Legionellosis

- Very severe pneumonia

- Legionella pneumophila (gram-neg rod)

- Found in hot water

- Transmitted by inhaling aerosols; not transmitted from human to human

- Symptoms: Mild but persistent respiratory symptoms; very high fever, cough, headache

- Treatment: Tetracyclines

Psittacosis (Ornithosis)

- Chlamydophila psittaci (Gram-neg intracellular bacterium)

- Transmitted to humans by elementary bodies from bird droppings

- Reorganizes into reticulate body after being phagocytized

- Symptoms: If any, are fever, headache, chills

- Treatment: Tetracyclines

Chlamydial Pneumonia

- Chlamydophila pneumoniae

- Transmitted from human to human

- Symptoms: Mild respiratory illness common in young people; resembles mycoplasmal pneumonia

- Treatment: Tetracyclines

Q Fever

- Causative agent: Coxiella burnetii

- Reservoir: Large animals

- Tick vector

- mammals to humans via tick

- Can be transmitted via unpasteurized milk

- Symptoms: Mild respiratory disease lasting 1-2 weeks; occasional complications such as endocarditis occur.

- Treatment: Doxycycline and chloroquine

Viral Diseases of the Lower Respiratory System

"For a virus to reach the LRS, it has to pass numerous defenses designed to trap and destroy it."

- Viral pneumonia occurs as a complication of influenza, measles, or chickenpox. (atypical type)

- Viral etiology suspected if no other cause is determined

Respiratory Syncytial Virus (RSV)

- Common in infants; 4500 deaths annually

- Causes cell fusion (syncytium) in cell culture

- Symptoms: Pneumonia in infants

- Happens sporadically

Influenza (Flu)

- major player

- Symptoms: Chills, fever, headache, and muscle aches (no intestinal symptoms)

- 1% mortality rate, very young and very old (10,000 - 20,000 annually die in U.S.)

- Prophylaxis: Annual multivalent vaccine

- Humans are not the only species that get the flu (Virus jumps species)

- Antigenic shift (Major change): Pandemic outbreaks, major change in structure, none is immune.

- Antigenic drift (Annual change): Annual flu shots, happens every yr.

- Flu viruses mutate, which is why you need to get vaccine annually.

- Usually unique to species, but it can mutate so much that it can jump species.

Influenza virus structure

- Classified by ratio of spikes

- Hemagglutinin (HA) spikes used for attachment to host cells.

- Neuraminidase (NA) spikes used to release virus from cell.

- It has: DNA, Protein Coat, Capsule, Spikes

- Spikes mutate

- Immunizations are made towards the spikes.

Cold vs. Flu

Fever

Histoplasmosis

- Histoplasma capsulatum, dimorphic fungus

- Disease resembles TB

- Associated with "bird droppings"

- Treatment: Amphotericin B

Coccidioidomycosis

- a.k.a. Valley Fever

- fungal

- Causative agent: Coccidioides immitis

- Reservoir: Desert soils of Southwest U.S.

- Symptoms: Fever, coughing, weight loss

- Treatment: Amphotericin B

Pneumocystis Pneumonia

- fungal

- Causative agent: Pneumocystis jirovecii

- Reservoir: Unknown, possibly humans or soil

- Symptoms: Pneumonia

- Treatment: Trimethoprim

Blastomycosis

- fungal

- Causative agent: Blastomyces dermatitidis

- Reservoir: Soil in Mississippi valley area

- Symptoms: Abscesses, extensive tissue damage

- Treatment: Amphotericin B

Aspergillus fumigatus (Aspergilliosis)

- systemic

- Compost piles

- Predisposing factors: immunocompromised state, cancer, diabetes.