Download Rocky Mountain Spotted Fever

Part IV Infectious Diseases
TABLE 22.5
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Streptococcus pyogenes Versus Staphylococcus aureus
Streptococcus pyogenes
Staphylococcus aureus
Morphology
Chains of Gram-positive cocci
Clusters of Gram-positive cocci
Growth
characteristics
Beta-hemolytic colonies; catalase negative, coagulase
negative, obligate fermenter
Golden, hemolytic colonies, catalase-positive,
coagulase-positive, facultative anaerobe
Virulence
factors
Cell wall contains group A polysaccharide, an Fc
receptor (protein G), and M protein. Bacterium produces
hemolysins (streptolysins O and S), streptokinase, DNase,
hyaluronidase, and others
Cell wall contains an Fc receptor (protein A). Bacterium
produces superantigens, hemolysins, leukocidin,
hyaluronidase, nuclease, protease, and others
Diseases
Impetigo, strep throat, wound infections, scarlet fever,
puerperal fever, toxic shock, and necrotizing fasciitis.
Complications: glomerulonephritis and rheumatic fever
Boils, staphylococcal scalded skin syndrome, wound
infections, abscesses, bone infections, impetigo, food
poisoning, and staphylococcal toxic shock syndrome
Even though impetigo is limited to the epidermis, streptococcal products are absorbed into the circulation. The immune
response to these proteins is thought to cause post-streptococcal
sequelae, particularly acute glomerulonephritis. post-streptococcal
sequelae, p. 489
glomerulonephritis, p. 490
Epidemiology
Impetigo is most common among poor young children living in hot,
humid areas. Person-to-person contact spreads the disease, as do
insects, and fomites such as toys and towels. Impetigo patients often
become throat and nasal carriers of S. pyogenes. fomites, p. 440
Signs and Symptoms
Rocky Mountain spotted fever begins suddenly with a headache,
pains in the muscles and joints, and fever. Within a few days of
infection, a rash characterized by faint pink spots appears on the
palms, wrists, ankles, and soles. This rash, caused by blood leaking from damaged vessels, spreads up the arms and legs to the rest
of the body (figure 22.6). Bleeding may occur at other sites, such
Treatment and Prevention
So far, S. pyogenes strains remain susceptible to penicillin. For
patients allergic to penicillin, erythromycin can be substituted.
People with impetigo should avoid contact with others to prevent spreading the bacteria. The transmission of impetigo can be
limited by keeping skin clean and avoiding sharing personal items
such as towels and washrags. Antiseptics and wound cleansing
also decrease the chance of infection. Table 22.6 summarizes the
main features of impetigo.
Rocky Mountain Spotted Fever
Rocky Mountain spotted fever (RMSF) was first recognized in
the Rocky Mountain area of the United States—thus its name.
The disease is caused by an obligate intracellular pathogen called
rickettsia and is transmitted by certain species of ticks, mites, and
the genus Rickettsia, p. 277
lice.
TABLE 22.6
FIGURE 22.6 Rash Caused by Rocky Mountain Spotted
Fever Characteristically, the rash begins on the arms and legs,
spreads centrally, and as shown in this photo, becomes hemorrhagic.
?
What processes cause this rash?
Impetigo
Signs and symptoms
Blisters that break, releasing plasma and pus; formation of golden-colored crusts; lymph node enlargement
Incubation period
2 to 5 days
Causative organisms
Streptococcus pyogenes, Staphylococcus aureus
Pathogenesis
Organisms entering the skin through minor breaks; certain strains of S. pyogenes that cause impetigo can also
cause glomerulonephritis
Epidemiology
Spread by direct contact with carriers or patients with impetigo, insects, and fomites
Treatment and prevention
An oral penicillin if cause is known to be S. pyogenes; otherwise, an anti-staphylococcal antibiotic orally or
topically. Cleanliness; care of skin injuries.
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