Lower respiratory system infections
ADVANCE ORGANIZER
The lower respiratory tract generally has no biota. Very efficient mechanisms are at work here and infections usually occur only in people whose defenses are impaired. Most infections of this area are generally known as pneumonia regardless of whether disease is caused by bacteria or viruses or fungi. Other infections include tuberculosis, Legionnaires’ disease and pertussis.
ANATOMY AND PHYSIOLOGY
Ciliated cells line the respiratory tract and remove microorganisms by sending the mucus out of the system. The lower respiratory system includes the trachea, bronchi, bronchioles and the alveoli. The lungs are covered and the chest is lined with pleural membranes.
BACTERIAL CAUSED DISEASES:
Pneumonia
Streptococcus pneumonia is the most common cause of pneumonia. There are many strain which have different capsule antigens. The capsules are responsible for virulence. Immunity is strain specific.
Klebsiella pneumonia is a particularly difficult pneumonia because it is difficult to treat because klebsiellae (a non-motile, encapsulated enterobacterium) is often resistant to antibiotics due to R factor plasmids. The bug can cause permanent damage to the lung [because it has an endotoxin and serious complications]. It too has a capsule that helps it escape phagocytosis.
Mycoplasma pneumonia is often referred to as “walking pneumonia” because it is often mild. Antibiotics that attack cell walls are useless in treatment of this because mycoplasma pneumoniae, slow growing aerobic bacteria, don’t have them. (So that cuts out penicillins and cephalosporins). Cold agglutinins are helpful in diagnosis.
Other bacterial infections
Whooping cough is caused by Bordetella pertusis, an encapsulated, aerobic gram negative rod. The name is descriptive–the symptoms include violent spasms of coughing and gasping and can be fatal for infants. Spread of the disease is enhanced by waning immunity in adults and adolescents. They can get a mild case of Pertussis and spread it to others.
Tuberculosis is caused by an acid fast rod, Mycobacterium tuberculosis. This is a tricky disease because the bug resists drying, disinfectants and many antibacterial medicines. The disease is very slowly progressive or can heal and remain latent for years and then reactivate. That means an infection with tuberculosis becomes a life long threat. Its way of evading the immune system is key in disease development. Granuloma formation is characteristic. The immune response favors delayed type hypersensitivity which contributes to pathogenesis.
Legionnaire’s disease occurs in normal lung only when there is a high infecting dose of Legionella pneumophila, a Gram-negative rod shaped bacterium common in the environment. Water aerosols are the usual source. In other cases, an additional underlying lung disease [like many things–smokers are in this category] or other impairment of host defenses is necessary for an infection to occur. Since this bacteria is hard to grow and stain, special techniques are required for its diagnosis. [page 15]
VIRAL INFECTIONS OF THE LUNG
SARS
Influenza
Orthomyxoviruses cause influenza. Type A viruses cause serious epidemics and can recur due to antigenic shifts and drifts in hemagglutinin and neuraminadase protein antigens. The deaths are usually caused by secondary infections. Antibody against hemagglutinin is protective. Reyes syndrome may sometimes (rarely) occur during recovery from influenza B and other viral infections–but not due to the virus itself.figures p201 onwards 10.4 HA and N, 10.5 sialic acid 10.3 entry, 10.7 cap , 10.8 bud. flu vaccine 275-6, mutation 304
FUNGAL INFECTIONS OF THE LUNG
Histoplasmosis occurs in tropical and temperate zones. The highest U.S. incidence is in the Mississippi River states and South Atlantic states. The fungus, Histoplasma capsulatum, is found in soils contaminated by the dropping of birds and bats. Thus cause bats live in caves–is a disease also known as Spelunkers disease. The disease can be confused with tuberculosis.
Coccidioidomycosis occurs in the hotter dry areas [it is also known as Valley Fever]. It is caused by a soil fungus, Coccidioides immitis. This is a barrel shaped arthrospore which turns to spherules in infected tissue. The disease can be confused with tuberculosis.