infestations and infections of the skin Flashcards
what is staphylococcus aureus like?
bacteria
expresses virulence factors that confer pathogenic properties
eg receptors that allow it to bind fibrin, that is found at injury sites
symptoms:
Ecthyma
Impetigo
Cellulitis
Folliculitis
- Furunculosis - Carbuncles
Staphylococcal scalded skin syndrome (SSSS)
Superinfects other dermatoses (e.g. atopic eczema, HSV, leg ulcers)
what are streptococcus like?
bacterial
Virulence:
Strepococcus pyogenes (β-haemolytic) attaches to epithelial surfaces via lipoteichoic acid portion of fimbriae
- Has M protein (anti-phagocytic) & hyaluronic acid capsule
- Produces erythrogenic exotoxins
- Produces streptolysins S and O
what are symptoms of streptococcal infections?
symptoms:
Ecthyma
Cellulitis
Impetigo
Erysipelas
Scarlet fever
Necrotizing fasciitis
Superinfects other dermatoses (e.g. leg ulcers)
what is folliculitis?
Follicular erythema; sometimes pustular.
May be infectious or non-infectious.
Eosinophilic (non-infectious) folliculitis is associated with HIV.
Recurrent cases may arise from nasal carriage of Staphylococcus aureus, particularly strains expressing Panton-Valentine leukocidin (PVL).
how is folliculitis treated?
Treatment:
Antibiotics (usually flucloxacillin or erythromycin)
Incision and drainage is required for furunculosis.
What is the difference between a furuncle and a carbuncle?
A furuncle is a deep follicular abscess
- Involvement with adjacent connected follicles = Carbuncle.
Carbuncle - more likely to lead to complications such as cellulitis and septicaemia
Why do some patients develop recurrent staphylococcal impetigo or recurrent furunculosis?
Establishment as a part of the resident microbial flora
- Abundant in nasal flora
Immune deficiency:
- Hypogammaglobulinaemia
- HyperIgE syndrome - deficiency
- Chronic granulomatous disease
- AIDS
- Diabetes Mellitus
what is panton valentine leukocidin staphylococcus aureus?
β-pore-forming exotoxin
Leukocyte destruction and tissue necrosis
Higher morbidity, mortality and transmissibility
Skin:
- Recurrent and painful abscesses
- Folliculitis
- Cellulitis
- Often painful, more than 1 site, recurrent, present in contacts
Extracutaneous:
- Necrotising pneumonia
- Necrotising fasciitis
- Purpura fulminans
what is the risk of acquiring PVL staphylococcus aureas?
Risk of acquiring - 5 C’s
Close Contact – e.g. hugging, contact sports
Contaminated items , e.g. gym equipment, towels or razors.
Crowding –crowded living conditions such as e.g. military accommodation, prisons and boarding schools.
Cleanliness (of environment)
Cuts and grazes – having a cut or graze will allow the bacteria to enter the body
how is PVL staphylococcus aureas treated?
Consult local microbiologist / guidelines
Antibiotics (often tetracycline)
Decolonisation – often:
- Chlorhexidine body wash for 7 days
- Nasal application of mupirocin ointment , 5 days)
Treatment of close contacts
what is pseudomonal folliculitis?
Associated with hot tub use, swimming pools and depilatories, wet suit
Appears 1-3 days after exposure, as a diffuse truncal eruption.
Follicular erythematous papule
Rarely: abscesses, lymphangitis and fever.
Most cases self-limited – no treatment required.
Severe or recurrent cases can be treated with oral ciprofloxacin
what is cellulitis?
Infection of lower dermis and subcutaneous tissue
Tender swelling with ill-defined, blanching erythema or oedema
Most cases: Streptococcus pyogenes & Staphylococcus aureus
Oedema is a predisposing factor
Treatment: systemic antibiotics
what is impetigo?
Superficial bacterial infection, stuck-on, honey-coloured crusts overlying an erosion.
Caused by
- Streptococci (non-bullous) (bullae = blisters)
or
- Staphylococci (bullous)
Caused by exfoliative toxins A & B, split epidermis by targeting desmoglein I.
Often affects face (perioral, ears, nares (nostrils)).
Treated with topical +/- systemic antibiotics.
what is impetiginisation?
Occurs in atopic dermatitis, superficical infection
- Gold crust
- Staphylococcus aureus
what is ecthyma?
Severe form of streptococcal impetigo
Thick crust overlying a punch out ulceration surrounded by erythema
Usually on lower extremities
what is Staphylococcal Scalded Skin Syndrome?
Neonates, infants or immunocompromised adults
Due to exfoliative toxin (same as in bullous impetigo)
Infection occurs at distant site (ie conjunctivitis or abscess) (so nit at same site as scalded skin)
∴ Organism cannot be cultured from denuded skin.
In neonates, kidneys cannot excrete the exfoliative toxin quickly enough
→ Diffuse tender erythema that
→ Rapid progression to flaccid bullae,
→ Wrinkle and exfoliate, leaving oozing erythematous base
Clinically resembles Stevens-Johnson syndrome / toxic epidermal necrolysis
what is toxic shock syndrome (group a S. aureus)?
Febrile illness due to Group A Staphylococcus aureus strain that produces pyrogenic exotoxin TSST-1
Fever >38.9°C Hypotension Diffuse erythema Involvement of ≥ systems: – Gastrointestinal – Muscular – CNS - Renal - Hepatic
Mucous membranes (erythema)
Hematologic (platelets <100 000/mm3)
Desquamation predominantly of palms and soles 1-2 weeks after resolution of erythema
what is erythrasma?
Infection of Corynebacterium minutissimum
Well demarcated patches in intertriginous areas (eg. armpits)
- initially pink
- Become brown and scaly
what is pitted keratolysis?
Pitted erosions of soles
Caused by Corynebacteria
Treated with topical clindamycin.
what is erysipeloid?
Erythema and oedema of the hand after handling contaminated raw fish or meat.
Extends slowly over weeks.
Erysipelothrix rhusiopathiae
what is anthrax (in terms of the skin)?
Painless necrotic ulcer with surrounding oedema and regional lymphadenopathy (with pain in lymph nodes) at the site of contact with hides, bone meal or wool infected with Bacillus anthracis.
what is blistering distal dactylitis?
Rare infection caused by Streptococcus pyogenes or Staphylococcus aureus
Typically - young children
1 or more tender superficial bullae on erythematous base on the volar fat pad of a finger
Toes may rarely be affected
what is erysipelas?
Infection of deep dermis and subcutis (similar to cellulitis)
Caused by β-haemolytic streptococci or Staphylococcus aureus
Painful
Prodrome of malaise, fever, headache.
Presents as erythematous indurated plaque with a sharply demarcated border and a cliff-drop edge
+/- blistering
Face or limb
+/- red streak of lymphangitis and local lymphadenopathy.
Portal of entry must be sought (e.g. tinea pedis).
Systemic symptoms (fever, malaise).
Treated with intravenous antibiotics.
what is scarlet fever?
Primarily a disease of children
Caused by upper respiratory tract infection with erythrogenic toxin-producing Streptococcus pyogenes
Preceded by sore throat, headache, malaise, chills, anorexia and fever
Eruption begins 12-48 hours later
- Blanchable tiny pinkish-red spots on chest, neck and axillae
- Spread to whole body within 12 hours
- Sandpaper-like texture
Complications: otitis, mastoiditis, sinusitis, pneumonia, myocarditis, hepatitis, meningitis, rheumatic fever, acute glomerulonephritis
what is necrotising faciitis?
Initial dusky induration (usually of a limb), followed by rapid painful necrosis of skin, connective tissue and muscle.
Potentially fatal
Usually synergistic: streptococci, staphylococci, enterobacteriaceae and anaerobes.
Prompt diagnosis essential (requires high index of suspicion), followed by broad-spectrum parenteral antibiotics and surgical debridement.
MRI can aid diagnosis.
Blood and tissue cultures can determine organisms and sensitivities.
Mortality is high.
Can affect the scrotum (Fournier’s gangrene).
what is Atypical Mycobacterial Infection?
Important cause of infection in immunosuppressed states.
Mycobacterium marinum causes indolent granulomatous ulcers (fish-tank granuloma) in healthy people
- Sporotrichoid spread (spread olong the lymphatics)
Mycobacterium chelonae & abscessus - puncture wounds, tattoos, skin trauma or surgery
Mycobacterium ulcerans: an important cause of limb ulceration in Africa (Buruli ulcer) or Australia (Searle’s ulcer).
what is borreliosis (lyme disease?
Annular erythema develops at site of the bite of a Borrelia-infected tick
Bite form Ixodes tick infected with Borrelia burgdorferi
Initial cutaneous manifestation: Erythema migrans (only in 75%)
- Erythematous papule at the bite site
- Progression to annular erythema of >20cm
1-30 days after infection, fever, headache
Multiple secondary lesions develop - similar but smaller to initial lesion
Neuroborreliosis:
- Facial palsy / other CN palsies
- Aseptic meningitis
- Polyradiculitis
Arthritis – painful and swollen large joints (knee is the most affected join)
Carditis
Serology not sensitive
Histopathology - non-specific
High index of suspicion required for diagnosis
what is tularaemia?
Caused by Francisella tularensis
Acquired through:
- Handling infected animals (squirrels and rabbits)
- Tick bites
- Deerfly bites
Ulceroglandular form
Primary skin lesion is small papules at inoculation site that rapidly necroses – leading to painful ulceration
+/- local cellulitis
Painful regional lymphadenopathy
Systemic symptoms: fever, chills, headache and malaise
what is ecthyma gangrenosum?
Pseudomonas aeruginosa
Usually occurs in neutropaenic patients
Red macule(s) → oedematous → haemorrhagic bullae.
May ulcerate in late stages or form an eschar surrounded by erythema
