Diseases Of The Respiratory System

Bacterial Diseases of the Lower Respiratory System

Many of the same microorganisms that infect the upper respiratory system also infect the lower respiratory system.

Diseases of the lower respiratory system include bronchitis and pneumonia.

Pertussis (Whooping Cough)

Caused by Bordetella pertussis, which produces a very potent exotoxin.

The initial stage, or the catarrhal stage, presents like a cold.

The second, or paroxysmal stage, is characterized by mucus accumulations in the trachea and bronchi, which cause deep coughing.

The third, or convalescence stage, can last for months.

Laboratory diagnosis is based on isolation of bacteria on Bordet-Gengou medium and serological tests.

Prevention: Immunization with DPT

Ciliated Cells of the Respiratory System Infected with Bordetella pertussis

Tuberculosis

Caused by Mycobacterium tuberculosis.

The bacterium is acid-fast due to lipid in the cell wall, which makes it very resistant to drying and disinfectants.

Mycobacterium tuberculosis

Filamentous fungus-like growth caused by cord factor

The bacteria may survive phagocytosis and may reproduce in macrophages.

Transmission is by droplet nuclei (respiratory aerosols).

Lesions are called tubercles; dead macrophages and bacteria form caseous lesions that may calcify and appear on X ray as a Ghon complex.

Liquefaction of the caseous lesion results in a tuberculous cavity in which M. tuberculosis can grow.

Pathogenesis of Tuberculosis



New foci of infection can develop when a caseous lesion ruptures and releases bacteria into blood or lymph vessels; this is called miliary tuberculosis.

Miliary tuberculosis is characterized by weight loss, coughing, and loss of vigor.

Chemotherapy usually involves two drugs taken for 1 - 2 years; multidrug-resistant M. tuberculosis is becoming prevalent.

A positive tuberculin test is used to determine previous exposure; it is not diagnostic because a positive test may indicate an active case, a previous infection, or vaccination and immunity.

Tuberculin Skin Test

Laboratory diagnosis is based on isolation and identification - takes up to 8 weeks.

Mycobacterium bovis causes bovine tuberculosis and can be transmitted to humans by unpasteurized milk.

M. bovis infections usually affect the bones or lymphatic system.

Prevention is by case finding and treatment.

The BCG vaccine is a live, avirulent culture of M. bovis; It is of variable utility and is not used in the U.S.

A related group of organisms, M. avium-intracellulare complex, infects patients in the late stages of HIV infection.

U.S. Distribution of Tuberculosis

Bacterial Pneumonias

Mostly caused by normal flora from the mouth and throat. The most common causes are:

Typical pneumonia is caused by S. pneumoniae.

Atypical pneumonias are caused by other microorganisms.

Pneumococcal Pneumonia

Pneumococcal pneumonia is caused by encapsulated Streptococcus pneumoniae.

Symptoms are rust colored sputum, fever, difficult breathing, and chest pain.

The lungs have reddish appearance due to dilation of blood vessels. Alveoli fill with erythrocytes and fluid.

Initial diagnosis is made by X-rays. Laboratory diagnosis is by isolation and identification based on production of alpha-hemolysins, inhibition by optochin, bile solubility, and through serological tests.

The treatment of choice is penicillin.

A purified capsular vaccine consisting of capsular material from 23 serotypes of S. pneumoniae is available.

Streptococcus pneumoniae

Haemophilus influenzae Pneumonia

Alcoholism, poor nutrition, cancer, and diabetes are predisposing factors for H. influenzae pneumonia.

H. influenzae is a gram-negative coccobacillus.

Mycoplasmal Pneumonia

Mycoplasmal pneumonia (primary atypical pneumonia or walking pneumonia) is caused by the pleomorphic rod Mycoplasma pneumoniae.

Mycoplasma pneumoniae produces characteristic fried egg colonies after 2 weeks' incubation on enriched media containing horse serum and yeast extract.

Symptoms are low grade fever, cough, and headache. Mortality rate is less than 1%.

Diagnosed by PCR or complement fixation.

The treatment of choice is tetracycline or erythromycin.

Colonies of Mycoplasma pneumoniae

Legionellosis

Caused by the aerobic gram-negative rod Legionella pneumophila.

The organism grows in water and is spread through the air; it is resistant to chlorine.

Person to person spread is not likely.

High risk groups are males over 50, heavy smokers, alcohol abusers, and those with chronic illness.

Bacterial culture, FA tests and DNA probes are used for laboratory diagnosis.

The treatment of choice is erythromycin.

Psittacosis (Ornithosis)

Caused by the gram-negative obligate intracellular parasite Chlamydia psittaci.

The organisms is transmitted by contact with bird droppings and causes a form of pneumonia.

Symptoms include fever, headaches, and chill.

Elementary bodies allow the bacteria to survive outside a host.

Because it is an obligate intracellular parasite the bacterium must be isolated in embryonated eggs, mice, or cell culture; identification is based on FA techniques or complement fixation.

The treatment of choice is tetracycline. No effective immunity is produced.

Chlamydial Pneumonia

Chlamydia pneumoniae causes pneumonia; it is transmitted from person to person.

Tetracycline is used for treatment.

Q Fever

Caused by the obligate intracellular parasite Coxiella burnetii.

It is usually transmitted by unpasteurized milk or inhalation of aerosols in dairy barns.

The infection is usually subclinical. Symptoms include fever, chills, chest pain, and headache.

Laboratory diagnosis by culture in embryonated eggs or cell culture.

The treatment of choice is tetracycline.

Coxiella burnetii

Other Bacterial Pneumonias

Gram positive bacteria that cause pneumonia include S. aureus and S. pyogenes.

Gram-negative bacteria that cause pneumonia include Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Branhamella catarrhalis, and Enterobacter species.

Klebsiella pneumonia

Caused by Klebsiella pneumoniae.

Klebsiella pneumonia results in lung abscesses and permanent lung damage; the mortality rate is 85%.

The treatment of choice is cephalosporins or gentamicin.