epidemiology: Propionibacterium acnes; normal
bacterial microbiota; up to 85% of adolescents suffer from
acne at some time
pathogenesis: hair follicle infection that spreads
into surrounding tissue, generating an abscess; complications
- skin disfigurement (scars)
treatment: tetracycline, blue
light therapy, oral contraceptives, vitamin A derivatives
(Retin A cream ... can cause dry skin; Accutane,
an oral medication which is unfortunately also a teratogen
(it causes
birth defects, so it should
not be used by pregnant women) ... Accutane
may be linked to psychiatric problems, including a potential
risk for suicide;
Americans spend ~$1 billion/year on prescription drugs to
treat acne
prevention: decrease sebum accumulation by thorough
personal hygiene and depress bacterial growth with topical
peroxide-containing medications
Impetigo
epidemiology: Staphylococcus aureus and/or Streptococcus
pyogenes; this bacterial disease is highly contagious in children
pathogenesis: superficial infection leads to formation of
thin-walled abscesses that look like blisters or "weeping" lesions
with scabs; complications - "blood poisoning"
(toxemia or septicemia)
treatment: bacitracin salve or other antimicrobial agents
resistant to bacterial enzymes that destroy penicillins
prevention: personal hygiene; avoid contact with lesions
on other people
Furuncle (boil)
epidemiology: Staphylococcus aureus; normal bacterial
microbiota in up to 30% of normal humans
pathogenesis: infected skin follicle leads to formation of
an abscess;
complications - multiple abscesses (carbuncles);
"blood poisoning" (toxemia) due to systemic distribution of toxin
or bacteria; osteomyelitis
treatment:
"lance" abscess; treat with bacitracin, vancomycin or other antimicrobial
agents that are resistant to bacterial enzymes that destroy penicillins
prevention: personal hygiene; avoid contact with boils on
other people
Necrotizing
Fasciitis
epidemiology: Streptococcus pyogenes (bacterium); according
to CDC, there were 500-1500 cases in the US in 1996 and 20%
were fatal
pathogenesis: rapidly-spreading infection leads to
destruction of tissues at sites of infection ... aka Flesh-Eating
Disease; complications - formation of abscesses throughout
the body and "blood poisoning"
(toxemia or septicemia)
treatment:
penicillin, erythromycin, or tetracycline; surgery, when necessary
prevention: personal hygiene
Gangrene (myonecrosis)
epidemiology: Clostridium
perfringens; wound is infected with endospores of this bacterium from soil, clothing,
etc.
pathogenesis: superficial infection leads
to cellulitis, then to myonecrosis due
to toxins; complications - death due to CNS damage caused by toxins (sometimes complicated
by gas formation, hence the name "gas"
gangrene)
treatment: debridement, penicillin; hyperbaric
chamber (exposure to very high concentrations of oxygen kills this anaerobe)
prevention: early treatment may prevent full-blown disease
Tetanus
epidemiology: Clostridium
tetani; endospores of
this bacterium enter body via animal bites, scratches, puncture wounds;
fewer than 10 cases per year in US
pathogenesis: toxin (tetanospasmin) causes CNS damage
(4-21 days); complications - respiratory failure causes death (70% of
patients die)
prevention: antitoxin, vaccine (DPT
vaccine @ 2, 4, 6, 18 months and Td
vaccine boosters at 7-10 year intervals)
Candidiasis
epidemiology: Candida
albicans, this dimorphic fungus
is a member of the normal microbiota; likelihood of developing disease
is enhanced by chronic skin moisture, especially in immunosuppressed
individuals (AIDS, diabetes, etc.)
pathogenesis: as Candida grows on the skin, it induces a
bright red inflammation, blister-like superficial lesions or more
severe lesions all of which are perhaps related to hypersensitivity;
it sometimes occurs around the mouth (angular chelitis); complications
include systemic infection, which can lead to fulminating disease
and death
treatment: clotrimazole, miconazole or nystatin for skin
infections; oral ketoconazole for systemic infections
epidemiology: dermatophytic fungi such as Epidermophyton, Microsporium,
or Trichophyton; prevalent in athletes
pathogenesis: superficial skin infection causes granulomas on
head/scalp (tinea capitis), groin (tinea curis), body (tinea corporus),
foot (tinea pedis)
treatment: lamisil (terbinafine-HCl cream ... topical); shampoo
containing selenium; ketoconazole or itraconazole for initial antimicrobial
agent therapy; griseofulvin (oral) for chronic infections
prevention: avoid contact with lesions on other people's
skin
Warts
epidemiology: Human
Papilloma viruses are transmitted via scratches
pathogenesis: skin disfiguration from chronic benign tumors
treatment:
remove (excise)
wart by surgery (minor surgery, cryosurgery or lasersurgery) or by the
use of chemicals such as salicylic acid
prevention: avoid contact with warts on other people
Cutaneous Herpes
epidemiology: Herpes
Simplex Virus 1 (HSV-1)
is transmitted by direct contact; immunocompromised people are
especially vulnerable
pathogenesis:
recurrent chronic lesions (blisters)
on face, fingers, hands ...
becomes latent in local nerves and exhibits recurrence during periods of stress (physical
or psychological); herpes means "to creep"
treatment: acyclovir (zovirax) shortens episode, slows recurrence; valtrex is a second
generation version of zovirax ... works better
prevention: avoid contact with skin sores on other people
Lyme Disease
epidemiology:
Borrelia burgdorferi (bacterium) is spread by the nymph stage (poppy-seed
sized) of deer (black-legged) ticks ... it takes ~36 hours for the tick to infect
you with enough bacteria to cause disease
reservoirs are white-tailed deer and white-footed mice
15,000 cases reported in the US each year, mostly in children 2-15 and adults
30-55 years old who live in the Northeast and upper Midwest
Lyme
disease was first discovered near Lyme, CT
most frequently diagnosed tick-borne disease in the US
pathogenesis: - 60-85% of patients develop an expanding, ring-shaped ("Bull's-eye")
red rash (erythema migrans) at the site of a tick-bite ... after 3 days to one
month; accompanied by flu-like symptoms (malaise and fatigue, headache, fever and chills,
nausea, muscle and joint pain, neck stiffness) and patients may develop secondary skin lesions,
facial paralysis, forgetfulness; chronic, untreated systemic infection leads to arthritis,
heart inflammation, neurological abnormalities (weeks to months); nerve demyelination may
lead to multiple sclerosis-like symptoms (years after infection)
treatment: ceftin (cefuroxime axetil), penicillin or tetracycline (after diagnosis
with a newly-approved test kit, "PreVue B"); although there is controversy, it appears that
long-term intravenous antimicrobial agent therapy may be required in chronic cases
prevention: vaccine ("LYMErix")
was approved for
people from age 15 to 70, but not for those most likely to get the
disease, those under 15; this vaccine was subsequently removed from
the market amid allegations that it might cause
the very signs and symptoms Lyme disease causes; it is important
to avoid tick-bite (wear
protective clothing, use tick repellent, remove attached ticks) and
protect your pets
Anthrax
epidemiology: Bacillus
anthracis, an endospore-forming soil bacterium; this zoonotic
disease primarily affects grazing animals such as cattle, sheep and
goats, but can be transmitted to humans by contact with the endospores,
either via skin wounds or by inhalation; this disease is considered
to be a good candidate for biological warfare, and has been used in
terrorist activities ...CDC
Emergency Preparedness and Response
pathogenesis:
as endospores germinate, the vegetative bacterial cells begin to produce
a necrotizing toxin that causes development of pustular lesions
called eschars characterized
by necrotic centers that will eventually be filled with black fluid; complications include fulminating
septicemia that frequently leads to death, especially from the pulmonary
form of the disease
treatment: penicillin ... cipro (ciprofloxacin) was approved
in 2000
prevention: vaccine; avoid contact with endospore-contaminated
articles such as unwashed or unsterilized wool, goat hair, cattle hides,
etc.
Rabies
epidemiology:
Rabies Virus is
transmitted via bites of infected animals (bats,
raccoons, skunks, dogs, etc.) ... some
think that this disease inspired the vampire legend
pathogenesis:
CNS damage leads to death in 2-8 weeks
treatment: TLC
prevention: vaccine
(only disease known for which the vaccine can sometimes prevent
onset of disease, even after infection has occurred)
Encephalitis
epidemiology:Encephalitis
viruses are transmitted by mosquitoes (Culex tarsalis;
others); reservoirs
are other animals, including birds, reptiles and horses; found in
many parts of the world; infection
is most prevalent in Summer and Fall; ~600 primary cases of encephalitis
(not including West Nile) per year in the US (~100 post-infection
cases); West
Nile Fever is a recently emerging
encephalitic disease in the US; we spend ~$150
million per year trying to minimize encephalitis virus transmission
pathogenesis:
mosquito "injects" virus into bloodstream; virus replicates in the CNS,
causing fever and headache, vomiting, stiff back and neck, drowsiness,
tremors, loss of coordination, convulsions, seizures; complications
- may lead to coma as a result of CNS damage (can lead to retardation,
paralysis) and death occurs in 1-60%, depending upon the virus responsible
treatment: TLC ... management of symptoms and complications;
FDA has recently approved alpha-interferon as a possible treatment for
West Nile Fever
prevention: vaccines (none for West Nile Fever); mosquito repellent use;
mosquito control
Dengue
Fever
epidemiology:
caused by Dengue
Fever Virus, which is transmitted by Aedes
aegypti or Aedes albopictus mosquitoes;
endemic
in Africa, the Caribbean, Central and South America, Southeast
Asia and Australia; ~100 cases per year imported into the US by
travelers
pathogenesis: mosquito "injects" virus into
bloodstream; this rarely fatal disease is characterized by
sudden onset of high fever and rash together with severe
headache, and severe muscle, joint and eye pain (sometimes
called "breakbone" fever); complications include hemorrhagic
fever, with bleeding from gastrointestinal and other
mucosal membrane orifices of the body, which can lead to
shock and death in up to 20% of cases (mortality is ~1%
with appropriate treatment)
treatment: TLC, fluid replacement in hemorrhagic
fever cases
prevention: vaccines (under development); mosquito
repellent use; mosquito control
