Microbiology: A Systems Approach, 2nd ed.

Chapter 21: Infectious Diseases Affecting the Respiratory System

21.1 The Respiratory Tract and Its Defenses

• Most common place for infectious agents to gain access to the body

• Upper respiratory tract: mouth, nose, nasal cavity, sinuses, pharynx, epiglottis, larynx

• Lower respiratory tract: trachea, bronchi, bronchioles, lungs, alveoli

• Defneses– Nasal hair– Cilia– Mucus– Involuntary responses such as coughing, sneezing, and

swallowing– Macrophages– Secretory IgA against specific pathogens

Figure 21.1

21.2 Normal Biota of the Respiratory Tract

• Generally limited to the upper respiratory tract• Gram-positive bacteria (streptococci and

staphylococci) very common• Disease-causing bact4eria are present as normal

biota; can cause disease if their host becomes immunocompromised or if they are transferred to other hosts (Streptococcus pyogenes, Haemophilus influenza, Streptococcus pneumonia, Neisseria meningitides, Staphylococcus aureus)

• Normal biota perform microbial antagonism

21.3 Upper Respiratory Tract Diseases Caused by Microorganisms

• Rhinitis, or the Common Cold– Symptoms: sneezing, scratchy throat, runny nose

(rhinorrhea)– Symptoms begin 2-3 days after infection– Generally not accompanied by fever

Sinusitis– Commonly called a sinus infection– Most commonly caused by allergy– Can also be caused by infections or structural

problems– Generally follows a bout with the common cold– Symptoms: nasal congestion, pressure above the

nose or in the forehead, feeling of headache or toothache

– Facial swelling and tenderness common– Discharge appears opaque with a green or yellow

color in case of bacterial infection– Discharge caused by allergy is clear and may be

accompanied by itchy, watery eyes

Acute Otitis Media (Ear Infection)• Also a common sequel of rhinitis• Viral infections of the upper respiratory tract lead to

inflammation of the Eustachian tubes and buildup of fluid in the middle ear- can lead to bacterial multiplication in the fluids

• Bacteria can migrate along the eustachian tube from the upper respiratory tract, multiply rapidly, leads to pu production and continued fluid secretion (effusion)

• Chronic otitis media: when fluid remains in the middle ear for indefinite periods of time (may be caused by biofilm bacteria)

• Symptoms: sensation of fullness or pain in the ear, loss of hearing

• Untreated or severe infections can lead to eardrum rupture

Figure 21.2

Pharyngitis

• Inflammation of the throat• Pain and swelling, reddened mucosa, swollen

tonsils, sometime white packets of inflammatory products

• Mucous membranes may swell, affecting speech and swallowing

• Often results in foul-smelling breath• Incubation period: 2-5 days

Figure 21.3

Figure 21.4

Figure 21.5

Figure 21.7

Diphtheria

• Symptoms initially experienced in the upper respiratory tract

• Sore throat, lack of appetite, low-grade fever• Pseudomembrane forms on the tonsils or

pharynx

Figure 21.8

Figure 21.9

Figure 21.10

21.4 Diseases Caused by Microorganisms Affecting the Upper

and Lower Respiratory Tract

• A number of infectious agents affect both the upper and lower respiratory tract regions

• Most well-known: whopping cough, respiratory syncytial virus (RSV), and influenza

Whooping Cough• Also known as pertussis• Two distinct symptom phases

– Catarrhal stage• After incubation from 3 to 21 days• Bacteria in the respiratory tract cause what appear to be cold

symptoms (runny nose)• Lasts 1 to 2 weeks

– Paroxysmal stage• Severe and uncontrollable coughing• Violent coughing spasms can result in burst blood vessels in

the eyes or even vomiting• Followed by a long recovery (convalescent) phase

– Complete recovery requires weeks or even months– Other microorganisms can more easily cause secondary

infection

Respiratory Syncytial Virus Infection

• Produces giant multinucleated cells (synctia) in the respiratory tract

• Most prevalent cause of respiratory infection in the newborn age group

• First symptoms: fever that lasts approximately 3 days, rhinitis, pharyngitis, and otitis

• More serious infections give rise to symptoms of croup: coughing, wheezing, dyspnea, rales

Influenza

• Begins in the upper respiratory tract; serious cases may also affect the lower respiratory tract

• 1- to 4-day incubation period• Symptoms begin very quickly: headache,

chills, dry cough, body aches, fever, stuffy nose, and sore throat

• Extreme fatigue can last a few days or a few weeks

Figure 21.12

Figure 21.13

21.5 Lower Respiratory Tract Diseases Caused by Microorganisms

• Diseases that affect the bronchi, bronchioles, and lungs

• Tuberculosis and pneumonia

Tuberculosis

• Humans are easily infected with Mycobacterium tuberculosis but are resistant to the disease

• Only about 5% of infected people actually develop a clinical case of TB

• Untreated TB progresses slowly• Clinical TB is divided into primary tuberculosis,

secondary tuberculosis, and disseminated tuberculosis

Primary Tuberculosis• Period of hidden infection- asymptomatic or

accompanied by mild fever• After 3 to 4 weeks, immune system mounts a

cell-mediated assault- large influx of mononuclear cells into lungs

• Tubercles form• Frequently the centers of tubercles break down

into necrotic caseous lesions that gradually heal by calcification

• Tuberculin reaction

Figure 21.14

Figure 21.15

Secondary (Reactivation) Tuberculosis

• Live bacteria can remain dormant and become reactivated weeks, months, or years later

• Chronic tuberculosis: tubercles filled with bacteria expand and drain into bronchial tubes and upper respiratory tract; severe symptoms such as violent coughing, greenish or bloody sputum, low-grade fever, anorexia, weight loss, extreme fatigue, night sweats, chest pain

Extrapulmonary Tuberculosis

• Outside of the lungs• More common in immunosuppressed patients

and young children• Regional lymph nodes, kidneys, long bones,

genital tract, brain, and meninges• Complications are usually grave

Figure 21.17

Figure 21.18

Figure 21.19

Pneumonia• Anatomical diagnosis• Inflammatory condition of the lung in which fluid fills the

alveoli• Can be caused by a wide variety of different

microorganisms• Viral pneumonias are usually milder than bacterial• Community-acquired vs. nosocomial pneumonias• Begin with upper respiratory tract symptoms, including

runny nose and congestion• Headache common • Fever is often present• Onset of lung symptoms follows: chest pain, fever, cough,

discolored sputum

Figure 21.20

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Figure 21.26