Microbiology: A Systems Approach, 2 nd ed. Chapter 21: Infectious Diseases Affecting the Respiratory...
-
Upload
barnard-mcgee -
Category
Documents
-
view
220 -
download
3
Transcript of Microbiology: A Systems Approach, 2 nd ed. Chapter 21: Infectious Diseases Affecting the Respiratory...
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
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
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
Diphtheria
• Symptoms initially experienced in the upper respiratory tract
• Sore throat, lack of appetite, low-grade fever• Pseudomembrane forms on the tonsils or
pharynx
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
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
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
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