Exam 4- Chapter 24

Question 1

Streptococcal pharyngitis (strep throat)

Answer 1

• Caused by group A streptococci (GAS)
• Streptococcus pyogenes (Resistant to phagocytosis; Streptokinases lyse clots; Streptolysins are cytotoxic)
• Local inflammation, fever, tonsillitis, enlarged lymph nodes
• Diagnosis byenzyme immunoassay (EIA) tests

Question 2

Scarlet fever

Answer 2

-Erythrogenic toxin produced by lysogenized S. pyogenes

Question 3

Diphtheria

Answer 3

Caused by Corynebacterium diphtheriae (Gram-positive rod; pleomorphic)

• Forms a tough grayish membrane in the throat (Fibrin and dead tissue; Blocks passage of air to the lungs)
• Exotoxin produced by lysogenized bacteria (Circulates in the blood; damages the heart and kidneys)
• Cutaneous diphtheria (Forms skin ulcer)
• Prevented by DTaP vaccine (Diphtheria toxoid)

Question 4

Otitis media

Answer 4

• Infection of the middle ear (Formation of pus puts pressure on the eardrum)
• Streptococcus pneumoniae (35%)
• Common in childhood due to smaller auditory tube
• Treated with broad-spectrum penicillins

Question 5

The Common Cold

Answer 5

• Rhinoviruses (30–50%) (Thrive in temperatures lower than body temperature)
• Coronaviruses (10–15%)
• Sneezing, nasal secretion, congestion (Can lead to laryngitis and otitis media)
• Not accompanied by fever
• Antibiotics are of no use
• Relief via cough suppressants and antihistamines

Question 6

Pertussis (Whooping Cough)

Answer 6

• Caused by Bordetella pertussis (Gram-negative coccobacillus)
• Produces a capsule (Allows attachment to ciliated cells in the trachea; Destroys ciliated cells and shuts down the ciliary escalator)
• Tracheal cytotoxin of cell wall damages ciliated cells
• Pertussis toxin enters the bloodstream
• Prevented by DTaPvaccine
• Treated with erythromycin or other macrolides

Question 7

Whooping Cough stages

Answer 7

• Stage 1: catarrhal stage, like the common cold
• Stage 2: paroxysmal stage, violent coughing, gasping for air
• Stage 3: convalescence stage, may last for months

Question 8

Pneumococcal Pneumonia

Answer 8

-Caused by S. pneumoniae (Gram-positive; encapsulated diplococci; 90 serotypes)
-Infected alveoli of the lung fill with fluids and RBCs; interferes with oxygen uptake
Diagnosis: optochin-inhibition test, bile solubility test, or antigen in urine
-Treated with macrolides and fluoroquinolones
-Prevented with conjugated pneumococcal vaccine

Question 9

Mycoplasmal Pneumonia

Answer 9

• Mycoplasmal Pneumonia; Also called primary atypical pneumonia or walking pneumonia
• Caused by Mycoplasma pneumoniae (No cell wall)
• Mild but persistent respiratory symptoms; low fever, cough, headache
• Common in children and young adults
• “Fried-egg” appearance on media
• Diagnosis: PCR and serological testing
• Treated with tetracyclines

Question 10

Legionellosis

Answer 10

• Also called Legionnaires’disease
• Caused by Legionella pneumophila (Aerobic, gram-negative rod; Grows in water and air conditioning, biofilms, and waterborne amebae)
• Transmitted by inhaling aerosols; not transmitted person to person
• Symptoms: high fever and cough
• Similar to symptoms of Pontiac fever
• Treated with erythromycin and macrolides

Question 11

Respiratory Syncytial Virus (RSV)

Answer 11

-Most common viral respiratory disease in infants
(Almost all children are infected by age 2; 4500 deaths annually)
-Causes cell fusion (syncytium) in cell culture
-Coughing and wheezing for more than a week
-Diagnosis: serological test for viruses and antibodies
-Treated with ribavirin and palivizumab

Question 12

Histoplasmosis

Answer 12

• Caused by Histoplasma capsulatum (Dimorphic fungus; Yeast-form grows intracellularly in macrophages)
• Forms lung lesions; 0.1% of cases become a severe, generalized disease
• Acquired from airborne conidia in areas with bird or bat droppings (Limited geographical range in the United States)
• Treated with amphotericin B or itraconazole

Question 13

Coccidioidomycosis

Answer 13

• Also known as Valley fever or San Joaquin fever
• Caused by Coccidioides immitis (Dimorphic fungus)
• Arthroconidia found in alkaline desert soils of the American Southwest
• Form a spherule filled with endospores in tissues
• Most infections are not apparent; fever, coughing, weight loss (<1% of cases resemble tuberculosis)
• Treated with amphotericin B or imidazole drugs

Question 14

Tuberculosis

Answer 14

• Caused by Mycobacterium tuberculosis (Acid-fast rod; obligate aerobe; 20-hour generation time; Lipids in the cell wall make it resistant to drying and antimicrobials)
• Inhaled organisms are phagocytized by alveolar macrophages
• Mycolic acids in the cell wall stimulate an inflammatory response
• Organisms are isolated in the walled-off tubercle
• Tubercles heal and become calcified (Ghon’s complexes)
• Tubercle breaks down, releasing bacteria into the lungs and cardiovascular and lymphatic systems (Miliary tuberculosis: disseminated infection)
• 1/3 of the world’s population infected
• Leading cause of death for those with HIV
• BCG vaccine:live culture of avirulent M. bovis (Not widely used in the United States due to questionable effectiveness)

Question 15

Mycobacterium bovis

Answer 15

-Bovine tuberculosis; <1% of U.S. cases

Question 16

Mycobacterium avium-intracellulare complex (TB)

Answer 16

-Infects people with late-stage HIV infection

Question 17

Diagnosis of Tuberculosis

Answer 17

• Tuberculin skin test (Positive reaction means a current or previous infection; T cells react with purified protein derivative from the TB bacterium; Delayed hypersensitivity induration)
• Followed by an X-ray or CT exam, acid-fast staining of sputum, and culturing of bacteria
• New rapid blood test for IFN-γand PCR test (Higher specificity and less cross-reactivity)

Question 18

Treatment of Tuberculosis

Answer 18

• Minimum of 6 months of drug therapy due to slow growth and dormancy
• First-line drugs:isoniazid, ethambutol, pyrazinamide, rifampin
• Second-line drugs:aminoglycosides, fluoroquinolones, para-aminoslicyclic acid (PAS)
• Multi-drug-resistant (MDR) strains: resistant to first-line drugs
• Extensively drug-resistant (XDR) strains: resistant to second-line drugs

Question 19

Influenza (Flu)

Answer 19

• Influenzavirus (Contains eight RNA segments and an outer lipid bilayer)
• Chills, fever, headache, and muscle aches
• No intestinal symptoms
• 30,000 to 50,000 deaths in the United States annually
• Avian, swine, and mammalian strains (Swine serve as “mixing vessels” for new strains)

Question 20

Influenza spikes

Answer 20

• Hemagglutinin (HA) spikes (Recognize and attach to host cells)
• Neuraminidase (NA) spikes (Help the virus separate from the infected cell)
• Antigenic drift (Minor antigenic changes in HA and NA; Allow the virus to elude some host immunity)
• Antigenic shifts (Changes great enough to evade most immunity;Lead to pandemics; Involve the reassortment of the eight RNA segments)

Question 21

Influenza treatment and prevention

Answer 21

• Multivalent vaccine for the most important strains (Composition of the vaccine determined annually by the identification of circulating viruses; Labor-intensive to produce; Does not provide long-term immunity)
• Difficult to diagnose from clinical symptoms
• Treated with zanamivir (Relenza) and oseltamivir (Tamiflu) (Inhibits neuraminidase)