CN2 & 3: Mycoses & Lice Flashcards
Examples of these are dermatophytes (agents of ringworm, athletes foot) and infxns s/a tinea nigra and piedra, all infect keratinized tissues including pityriasis versicolor
Superficial and cutaneous mycoses
This includes chromoblastomycosis, mycetoma, and pheohypomycotic cyst
Subcutaneous mycoses
Occur primarily in immunocompromised px
Opportunistic
Superficial mycoses and their causative fungal agents
Pityriasis versicolor - Malassezia sp.
Tinea nigra - Hortea werneckii
White piedra - Trichosporon sp.
Black piedra - Piedreia hortae
PM, TH, WT, BP
Cutaneous mycoses and their causative fungal agents
Dermatophytosis - Microsporum sp., Trichophyton sp., And Epidermophyton floccosum
Candidiasis of skin, mucosa, or nails - Candida albicans and other cand
Subcutaneous mycoses and their causative fungal agents
Sporotrichosis - Sporothrix schenckii
Chromoblastomycosis - Phialophora vemucosa, Fonsecaea pedrosoi
Mycetoma - Pseudaescheria boydii, Madurella mycetomatis
Phaeohyphomycosis - Exophiala, Bipolaris, Exserohilum, and other cematiaceous molds
Endemic (primary, systemic) mycoses and their causative fungal agents
Coccidioidomycosis - Coccioides posadasii and immitis
Histoplasmosis - H. capsulatum
Blastomycosis - B. dermatitidis
Paracoccidioidomycosis - P. brasiliensis
Opportunistic mycoses and their causative fungal agents
Systemic candidiasis - C. albicans
Cryptococcus - Cryptococcus neoformans and Cryptococcus gattii
Aspergillosis - fumigatus
Hyalohyphomycosis - Fusarium, Paecilomyces, Trichosporon
Phaeohyphomycosis - Ciadopholalophora bantiana; sp of Alternaria, Cladosporium, Bipolaris, Exserohilum
Mucomycosis (zygomycosis) - Rhizoos, Absidia, Cuninghamella
Penicilliosis - Penicillium marneffei
What is the etiologic agent of Pityriasis or T. versicolor?
Malassezia furfur or Pityrosporum orbiculare (ovale)
Chronic, mild asymptomatic superficial infection involving most commonly the trunk (chest, upper back, arms, or abdomen)
Pityriasis or P. versicolor
Sharply marginated white macule with fine scaling plaques. Occur as discrete, serpentine, hyper – or hypopigmented maculae. Inflammation and irritation are minimal.
Superficial Mycoses – Pityriasis or Tinea Versicolor
Morphology: oval – or – bottle shaped cells that exhibit monopolar budding in the presence of a cell wall with a septum at the site of the bud scar. Small hyphal fragments are observed. Small yeasts without the presence of psudohyphae.
Malassezia furfur or Pityrosporum Orbiculare (ovale) – dermatophytes
Laboratory diagnosis: Direct microscopy of skin scrapings shows characteristic round yeast forms. Cluster of oval budding yeast cells 3.5 x 4.5 mm long with short, septae and occasionally branching hyphae. The microscopic appearance of the yeast is classically describe as “spaghetti and meatballs”
Malassezia furfur or Pityrosporum Orbiculare (ovale) – dermatophytes
What are are caused by fungi that infect only the superficial keratinized tissue (skin, hair, and nails)?
Cutaneous mycoses
The most important of these are the dermatophytes, a group of about 40 related fungi that belong to three genera:
Microsporum, Trichophyton, and Epidermiphyton
In skin they are diagnosed by the presence of hyaline, septate, branching hyphae or chains of arthroconidia.
Cutaneous mycoses
Dermatophytes are identified by their colonial appearance and microscopic morphology after growth for 2 weeks at 25C on what agar?
SDA
They develop cylindric, smooth – walled macroconidia and characteristic microconidia depending on the variety, colonies of T. mentagrophytes may be cottony to granular; both types display abundant grape – like clusters of spherical microconidia on terminal branches.
Trichophyton species - infect hair, skin, or nails
- Commonly found in primary isolates: coiled or spiral hyphae
What has a white, cottony surface and a deep red, nondiffusible pigment when viewed from the reverse side of the colony?
T. rubrum
What are small and piriform (tear – shaped). T tonsurans produces a flat, powdery to velvety colony on the obverse surface that becomes reddish – brown on reverse; and are mostly elongate?
Microconidia
Microsporum species tend to produce distinctive what?
Multicellular macroconidia with echinulate walls
What forms a colony with a white cottony surface and a deep yellow color
on reverse; the thick – walled, 8- to 15 celled macroconidia frequently have curved or hooked tips?
M. canis
What produces a tan, powdery colony and abundant thin – walled, four- to six-celled macroconidia?
M gypseum
Microsporum species infect only what?
Hair and skin
What is the only pathogen in this genus, produces only macroconidia, which are smooth – walled, clavate, two- to four-celled, and formed in small clusters?
Epidermophyton floccosum
The colonies are usually flat and velvety with a tan to olive – green tinge. It infects the skin and nails but not the hair.
E. floccosum
Flat feathery colonies w a central fold and yellow to dull gray-green pigment. Yellow to brown reverse pigment.
Microscopic: no microconidia, numerous thin and thick-walled, club-shaped macroconidia
E. floccosum
Flat and white to grey w widely spaced radial grooves. Tan to salmon reverse pigment. Salmon-pink pigment on PDA. No growth on polished rice.
Microscopic: Terminal chlamydoconidia and pectinate (comb-like) hyphae
M. audouinii
Flat and white to yellow, coarsely hairy, w closely spaced radial grooves. Yellow to orange reverse pigment. Yellow on PDA. Growth on polished rice.
Microscopic: few microconidia, numerous thick-walled and echinulate macroconidia w terminal knobs
M. canis
Flat and granular w tan to buff pigment, no reverse pigment.
Microscopic: few microconidia, numerous thinwalled macroconidia w/o knobs
M.gypseum
White to creamy w a cottony, mounded surface. None to light brown reverse pigment on PDA Urease positive.
Microscopic: Clustered round microconidia, rare cigar-shaped macroconidia, occasional spiral hyphae. Hair perforation (+)
T. mentagrophytes
Mounded white center w maroon periphery. Maroon reverse pigment. Cherry red on PDA. Urease negative.
Microscopic: few tear-shaped microconidia, rare pencil-shaped macro. HP (-)
T. rubrum
Heaped or folded and whitish. Colorless to yellow-tan reverse pigment.
Microscopic: knobby antler-like hyphae (chandeliers), numerous chlamydoconidia
T. schoenleinii
Suede-like w feathery periphery, white to yellow or maroon. Reverse pigment usually dark maroon, sometimes none to yellow. Partial thiamine requirement
Microscopic: numerous multiform microconidia and are rare cigar-shaped macroconidia
T. tonsurans
Small and heaped, though sometimes flat, white to yellow-grey. Reverse pigment none to yellow. Requires thiamine and usually inositol for growth.
Microscopic: chains of chlamydoconidia on SDA. Long and thin “rat-tail” macroconidia w thiamine
T. verrucosum
Waxy and heaped, deep purplish-red. Purple rev pig. Partial thiamine requirement.
Microscopic: Irregular hyphae w intercalary chlamydoconidia. No micro or macro on SDA, rare micro and macro w thiamine
T. violaceum
- Scrapings of the skin or nails, is collected using a scalpel blade or edge of a glass microscopic slide. KOH 5 – 10% is applied at the side of the coverslip. KOH solution and gentle heating softens keratin and highlights the dermatophytes.
- In potassium hydroxide 5 to 20% solution preparation, fungal hyphae appear as septate and branching structures.
Potassium hydroxide preparation (KOH)
- Hairs infected with microsporum spp. Fluoresce. Greenish. Darken room and illuminate affected site with wood lamp.
Coral red fluorescence of intertriginous site confirms diagnosis of erythrasma.
Wood lamp
- Specification of superficial fungi is based on the colonial morphology,
microscopic morphology metabolic characteristics. - Sabouraud’s dextrose agar is the most commonly used isolation medium. Facilitates growth of dermatophytes and inhibits growth of Non-Candida albicans, Protheca species, Cryptococcus.
Fungal culture
- Scales from the advancing border, subungual debris or affected hair are embedded in the medium
- Medium contains the pH indicator phenol red. Dermatophytes use proteins which result in excess ammonium ion and an alkaline environment.
Dermatophyte test medium
- Special stains: Periodic acid-schiff (PAS) highlights fungal elements in pink color or Grocott methenamine silver (GMS) in black color, within the stratum corneum or superficial epidermis
Histopathology
What infxn can be acquired by contact with contaminated floors (homes, health clubs, athletic locker rooms, or hotel rooms)?
T. rubrum infection
Dermatophyte infections can be acquired from three sources:
○ Most commonly from another person (usually by fomites, less so by direct skin-to-skin contact (Tinea gladiatorum)
○ From animals such as puppies or kittens
○ Least commonly from soil
What synthesize keratinases that digest keratin and sustain existence of fungi in keratinized structures?
Dermatophytes
What restrict dermatophyte pathogenecity?
Cell – mediated immunity and antimicrobial activity of polymorphonuclear leukocytes
○ Host factors that facilitate dermatophyte infections: atopy, topical and systemic glucocorticoids, ichthyosis, collagen vascular disease.
○ Local factors favoring infections: sweating, occlusion, occupational exposure, geographic location, high humidity (tropical or semitropical climates)
The infection begins with hyphal invasion of the skin of the scalp, with
subsequent spread down the keratinized wall of the hair follicle.
Infection of the hair takes place just above the hair root.
Tinea Capitis or ringworm
Etiologic agents of Tinea Capitis or ringworm
Microsporum and Trichophyton mentagrophytes
- scaling with minimal inflammation of the scalp
- affected hairs are dull gray & lusterless due to coating of spores & break off just above the level of the scalp
Non-inflammatory
*pustular folliculitis
* KERION = inflammatory
* aboggy mass studded with
& lusterless due to broken hairs oozes
purulent material
* Itchy and painful
* Fever and lymphadenopathy
Inflammatory
= Infection of the glabrous (smooth skin) other than involving the scalp, beard, face, hands, feet and groin
= Etiologic agents: E. flocossum and Trichophyton rubrum Species
Tinea Corporis
= Annular and well defined lesions with active margins, slightly raised, red and scaly with central clearing which maybe single or multiple.
Skin lesions (Tinea Corporis)
Diagnostic laboratory tests: Microscopic examination and
culture
= Infection of the groin; commonly affects male
= Etiologic agents: Arthropophilic dermatophytes like T. rubrum,
E. floccosum, T. mentagrophytes
Tinea Cruris
= Infection of the skin of the feet/hands sometimes toes/fingernails
= Etiologic agents: T. rubrum, E. flocossum, T. mentagrophytes var
interdigitale
= begins in the toe webs maceration, peeling and erythema and
soles rarely to dorsa of the feet
= Palmar skin feels very dry with powdery feeling of the skin
creases with concentric peeling scales fingernails later involve
= maybe pruritic and usually assymetrical
= Demonstration of hyphae on direct microscopy and isolation od
dermatophyte on culture
Tinea Pedis and Manuum
= Ringworm of the beard, also known as tinea sycosis and barber’s itch is not common disease. More common in farmers
= Involves the beard and mustache areas
= Etiologic agent: Trichophyton mentagrophytes
Clinical features: hair follicles
= Surrounded by inflammatory papules or pustules, often with
exudation and crusting. Involved hair are loose and easily
removed. Skin symptoms include pruritus, tenderness and pain.
= The clinical diagnosis is confirmed by the microscopic examination an culture
Tinea Barbae
It is defined as the infection of the nail plate by fungus and represents up to 30% of diagnosed superficial fungal infections. T. rubrum accounts for most
cases, but many fungi may be causative.
Other etiologic agents include E. floccosum and various species of Microsporum and Trichophyton molds.
Onychomycosis (Tinea Unguium)
It is caused by T. rubrum usually starts at the distal corner of the nail and involves the junction of the nail and its bed. A yellowish discoloration occurs, which spreads proximally as a streak in the nail. Later, subungal hyperkeratosis becomes prominent and spreads until the entire nail is affected. Gradually the entire nail becomes brittle and separated from its bed as a result of the piling up of subungal keratin. Fingernails and toenails present a similar appearance, and the skin of the soles is likely to be involved, with characteristic branny scaling and erythema.
Onychomycosis
It is caused by T. mentagrophytes is usually superficial, and there is not paronychial inflammation. The infection generally beings with scaling of the nail under the overhanging cuticle and remains localized to a portion of the nail. In time, however, the entire nail plate may be involved. White superficial onychomycosis is the name given to one type of superficial nail infection caused by this fungus in which small, chalky white spots appear on or in the nail plate.
Onychomycosis
The demonstration of fungus is mode by microscopic examination or by culture. The disease nail bed is examined with
KOH solution
Selenium sulfide shampoo – for Tinea capitis Zinc pyrithione Azoles cream/lotion Imidazoles cream/lotion Allylamines cream/lotion
TOPICAL TREATMENTS
Ketoconazole
Fluconazole
Itraconazole
Terfinafine
SYSTEMIC TREATMENTS
Ketoconazole (Imidazole group): Absorbed orally. Oral bioavailability is variable. Normal gastric acidity is required. Bioavailability is markedly depressed in patients taking H2-histaminergic receptor blocking agents and simultaneous administration of antacids may also impair absorption. The drug is distributed to most body tissues. The drug level achieved in the CNS is very low. It is metabolized in the liver and eliminated by the kidneys.
Pharmacokinetics
Ketoconazole (Imidazole group): Interfere with fungal cell membrane permeability by inhibiting the synthesis of ergosterol (14-alphademethyose), a microsomal cytochrome P450-dependent enzyme system and thus inhibiting the growth of the fungi.
Pharmacodynamics
Ketoconazole (Imidazole group)
Untoward effects:
- Nausea, anorexia, and vomiting are the most common side effects. Administration of the drug with food, at bedtime or in divided doses may improve tolerance.
- Allergic rash
- Pruritus without rash
- Menstrual irregularities in 10% of females
- Gynecomastia, decreased libido and potency in males
- Hypertension and fluid retention
This is a shampoo left on the scalp for 5 min three times a week.
Ketoconazole
Fluconazole (Triazole group): Absorbed readily and completely via the oral
route than the other azoles.
Bioavailability is not altered by food or gastric acidity. Fluconazole is distributed widely and diffuses readily into body fluids including sputum and saliva; concentrations in CSF are very high 50% to 90% of the simultaneous values in plasma since it enters the CNS readily. It is eliminated by the kidneys, largely in unchanged form.
Pharmacokinetics
Fluconazole (Triazole group): Interfere with fungal cell membrane permeability by inhibiting the synthesis of ergosterol (14-alphademethyose), a microsomal cytochrome P450-dependent enzyme system and thus inhibiting the growth of the fungi.
Pharmacodynamics
Untoward effects Fluconazole (Triazole group):
a. Nausea and vomiting
b. Headache
c. Skin rash
d. Abdominal pain
e. Diarrhea
f. Alopecia – occasionally seen
Itraconazole (Triazole group): Absorbed orally. Bioavailability reduced more than half – in fasting and reduced gastric acid or in cases of advanced AIDS. Distributed to most body tissues and not detected in CSF. Metabolized in the liver.
Pharmacokinetics
Itraconazole (Triazole group): Interfere with fungal cell membrane permeability by inhibiting the synthesis of ergosterol (14-alphademethyose), a microsomal cytochrome P450-dependent enzyme system and thus inhibiting the growth of the fungi.
Pharmacodynamics
What is an allylamine?
Terbenafine
It is effective in treatment of ringworm and in some cases on onychomycoss. It is less effective against candida speces and Malassezia furfura but the cream preparations can be used in cutaneous candidiasis and tinea versicolor.
Oral preparation: Terbenafine
fungicidal; It inhibits a fungal enzyme, squalene epoxidase. It causes accumulation on toxic levels of squalene, which can interfere with ergosterol synthesis.
Terbenafine
Terbenafine untoward effects:
Local irritation and allergic contact dermatitis
- Pharmacokinetics: Absorption is less than 0.5% after application to the intact skin. Metabolized in the liver and excreted in bile.
- Pharmacodynamics: Similar to the azoles systemic antifungal agents.
- Untoward effects: Erythema, stinging, edema, vesication, desquamation, pruritus, and urticaria.
Clotrimazole (Imidazole)
It is a predisposing factor for tinea infections. Because the disease often starts on the feet, the patient should be advised to dry the toes thoroughly after bathing. Dryness of the parts is essential if reinfection is to be avoided.
Hyperhydrosis
What are excellent dusting powders for the feet?
Tolnaftate powder (Tinactin powder) or Zeasorb medicated powder
Maybe dusted into socks and shoes to keep the feet dry. Periodic use of a topical anti-fungal agent may be required, especially when hot occlusive footwear is worn. Use of shower shoes whole bathing at home or in public facility washing feet with benzoyl peroxide bar directly after shower.
Plain talc, cornstarch, or rice powder
Important to examine home and school contacts of affected children for asymptomatic carriers and mild cases of tinea capitis. Ketoconazole or selenium sulfide shampoo may be helpful in eradicating the asymptomatic carrier state.
Combs, brushes and hats should be cleaned carefully and natural bristle brushes must be discarded.
Tinea Capitis
Apply powder containing Imidazoles or tolnaftate to areas prone to fungal infection after bathing
Tinea Cruris and Tinea Corporis
The lice are believed to survive for only about:
24 to 48 hours away from the human host, and therefore fumigation of homes is unnecessary
There are three types of lice known to infest humans:
- 1 Pediculosis humanus var capitis (head lice)
- 2 Pediculosis humanus var corporis (body lice)
- 3 Pediculosis (Phthirus) pubis (pubic or crab lice)
After an incubation of 9 – 12 days, the nymphal stage emerges from the egg, or nit and matures into an adult within another 10 – 15 days. Head and body lice move as rapidly as 23cm/min. head lice feed and reproduce on the human host, cementing their nits to the hair.
Life cycle of Pediculosis Capitis
The development from egg to egg – laying adult takes from 15 to 23 days. The optimal laboratory conditions for rearing head lice eggs are 27 – 31oC and 45 – 75% relative humidity:
Eggs
Nymph immature louse
Mature adult young mature female louse
Development stages (life cycle)
- are lain within 14 – 18 hours after mating: eggs are firmly attached to hair close to the scalp by “cement” or glue consisting of peptides and lipids that are very close in composition to some components of human hair (this is why egg – loosening agents might damage hair); egg stage is most resistant to pediculicides: egg casings found on hair are often called nits: nit may or may not contain a viable egg; egg stage takes from 7 to 12 days.
o Egg with eyespot nervous system started to develop around day
4th after laying, from this point in development eggs can be killed with agent that act on nervous system of lice
Eggs
this stage takes from 8.5 to 11 days; second
treatment by pediculicide need to be applied within this time
o 1st instar nymph nymph that hatched from the egg; the nymph has to start feeding immediately in order to survive
o 2nd instar nymph nymph after first molting (changing the
exoskeleton in order to grow)
o 3rd instar nymph nymph after second molting; on this stage lice become sufficiently mobile to undertake transfer to the next host
Nymph immature louse; nymph molts 3 times before becoming mature egg – laying adult
lays up to 9 eggs daily for period of 8 – 9 days after single insemination, with time her fecundity decreases; adults live for up to 32 days taking blood meals every 4 – 6 hours; during adulthood lice are most motivated to transfer to another
host; lice crawl with speed 6 – 30 cm per minute; they cannot jump or fly; in many cases lice are caught during the re – location and infestation is prevented.
Mature adult young mature female louse
Lice are ______, are flattened dorsoventrally, and have three pairs of legs that end in powerful claws of a diameter adapted to the region colonized.
1 – 3 mm long
0.5 –mm oval, whitish egg. Nonviable nits show an absence of an embryo or operulum.
Nits
insect with six legs, 1 – 2 mm in length, wingless, translucent grayish – white body that is red when engorged with blood.
Louse
The most common diagnostic sign of head lice is the live nits on the what part of the hair shaft?
Proximal
It is a synthetic pyrethonid that interferes with sodium transport proteins causing neurotoxicity and paralysis. Approved for use in infants of age. Preparations: lotion, gel, shampoo and mouse.
Permethrin
It is a synergist of pyrethrin. Kills mites louse and egg. Preparations: liquid, gels, shampoos. Applied to scalp and washed off after 10 minutes.
Pyrethrin with piperonyl butoxide (PBO)
- derived from extract of chrysanthemums
Applied to involved site for 8 – 12 h; binds to hair providing residual protection. Indicated in lindane – resistant cases. Should not be used in children younger than 6 months.
Malathion> 0.5% in 78% isopropyl alcohol (Ovide)
Applied for 4 min and then thoroughly washed off. (Not recommended for pregnant or lactating women.) Not totally ovicidal and lacks of residual activity; in that the incubation period of louse eggs is 6 – 10 days, the agents should be reapplied in
Lindane 1% shampoo
It is an organochloride compound that induce neuronal stimulation and eventual paralysis of parasites.
Untoward effect: neurotoxicity in children and adults and in patients with underlying skin disorder such as atopic dermatitis and psoriasis. Contraindicated in premature infants and patients with seizures.
Lindane
Epidemiology of Dermatophytes
● Dermatophyte infections begin in the skin after trauma and contact.
● There is evidence that host susceptibility may be enhanced by moisture, warmth, specific skin chemistry, composition of sebum and perspiration, youth, heavy exposure, and genetic predisposition.
● The incidence is higher in hot, humid climates and under crowded living conditions.
● Wearing shoes provides warmth and moisture, a setting for infections of the feet.
● The source of infection is soil or an infected animal in the case of geophilic and zoophilic dermatophytes, respectively.
● The conidia can remain viable for long periods.
● Anthropophilic species may be transmitted by direct contact or through fomites, such as contaminated towels, clothing, shared shower stalls, and similar examples.
Age of onset of head lice
3-11 years old
They are tiny, elongated, blood-sucking insects, soft-bodied, wingless with three pairs of legs (total of 6) all terminating in small claws, which enable them to grasp hair shafts or clothing fibers.
Lice
Head lice can survive off the scalp up to
55 hrs
Clinical manifestations of Pediculosis capitis
● Pediculosis capitis is more common in children, but occurs in adults also.
● Patients present with intense pruritus of the scalp, and often have posterior cervical lymphadenopathy.
● Excoriations and small specks of louse dung are noted on the scalp.
Pediculosis capitis is typically confined to the
Scalp
What can confirm the diagnosis of pediculosis capitis?
Finding live adult lice, immature nymphs, and/or viable appearing eggs
DDx for Pediculosis capitis
○ Scabies of the scalp: skin lesions are also present on other areas such as face, palms, and soles; pathognomonic sign which is burrow sign and finding of the etiologic agent (Sarcoptes scabiei)
○ Seborrheic dermatitis = on examination of the scalp shows seborrheic scales
What product applied to infested area(s) and washed off after 10 minutes. The hair should be combed with a fine-toothed comb to remove any remaining nits. Marketed over the counter as Nix a 1% cream rinse. The product is applied after shampooing the hair and scalp with a regular shampoo?
Permethrin shampoo
Prevention
● Avoid contact with possibly contaminated items such as hats, headsets, clothing, towels, combs, hair brushes, bedding, upholstery.
● The environment should be vacuumed.
● Bedding, clothing, and headgear should be washed and dried on the hot cycle of a dryer.
● Combs and brushes should be soaked in rubbing alcohol or Lysol 2% solution for 1 h.
● Families should look for lice routinely.
● Many schools in the United States adhere to a “no-nit” policy before children can return after infestation.
● All members of the affected household should be examined
● Floors, play areas, and furniture should be carefully
vacuumed to rémove any hairs with viable eggs.
