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Impetigo is a bacterial skin infection that usually affects children.Both group A beta-hemolitic streptococci and Staphylococcus aureus have been isolated from lesions of superficial impetigo .Primary lesions are eryhematous papules that ,after envolving into vesicles ,become crusted .Crusts are the typical feature at the last stage .Usually,impetigo is not associated with systemic symptoms are rare.Its prgression is benign and entails a self-limited process.
Superficial mycoses affect hair,nails and the outermost layer of skin.They spread from person or by fomites.The most important skin mycosis,dermatophytosis,is caused by Microsporum,Trichophyton and Epidermophyton species.Fungi invade stratum corneum and later,hair follicles.Tinea capitis(head)is characterized by alopecia on the scalp;tinea barbae(beard)tinea is an acute folliculitis developed on the beard area,wheras tinea corporis(body)is an eritematous dermatitis .
Pathophysiology of candidiases shows that predisposing factors(diabetes mellitus,use of antibiotics,corticoid or cytostatic therapy,excessive skin moisture,skin slits,etc.)play an important role in its development.Typically,it affects the skin folds of the hands and skin areas under the breasts and buttocks(intertrigo).In a large number of cases,it also presents onychomycosis associated with perionyxis.Among infants,candidiasis is one of the causes of diaper rash.
Pityriasis versicolor is a superficial cutaneous infection caused by the pathogenic transformation of a fungus commonly encountered on the surface of the skin.The etiologic agent of this infection is the Fungus Malassezia Furfur,also known in the yeast stage as Pityrosporum orbiculare.The fungus colonizes the superficial layers of the epidermis without penetrating deep in tissue .It is marked by the formation of irregular macules which appear lighter or darker according to the skin hue(versicolor)and light scaling.lesions occur on exposed body areas,mainly the trunk and upper limbs.
Common warts are skin lesions which presents as rough rounded hyperkeratotic papules of variable diameter and limited to the epidermis.They may be sessile or pediculate.Their etiological agent is a DNA virus called Human Papillomavirus,commonly known as HPV.It is located in the epidermis and mediates a significant proliferation of epithelial cells.
At present,more than 70 serotypes are known.Most papillomaviruses have distinct anatomic predilections,infecting only certain epidermal sites,and are associated with specific conditions.
Pediculosis is an infestation of different parts of the body by lice of the order Anoplura,genus Pediculus .It spreads by direct contact with infected persons an by sharing fomites(combs,brushes,clothes,etc.).Head lice in children is epidemic,especially at school.This form causes intense itching due to the intensely irritant saliva of the parasite.Scratching causes frequent overinfections and consistent development of secondary pyodermia and associated adenomegaly .
Scabies is an infestation by Sarcoptes scabiei var.hominis acarid.It spreads by direct contact with infected persons and causes an intense itchyrash .Signs and symptoms in children are very similar to those present in adults,i.e.,papillary lesions,blisters and burrows on thin skin areas (between the fingers ,wrists ,antecubital folds ,areolae,genitals,buttocks,umbilicus,etc.).Intense itchyrash causes almost constant excoriation due to scratching .
Varicella and herpes zoster
Apparently ,zoster infections are caused by a reactivation of a previously aquired varicella-zoster virus(VZV) infection.Varicella is the primary infection.After its occurrence,virions move afferently through sensory nerve endings to the sensory ganglions where the infection remains latent .At this location ,viral replication is low or almost non-existant.The mechanisms involved in reactivation are not clearly understood .When the reactivated virus finds the way to evade the host's immiune system ,there is a new migration which this time occurs efferently .Then ,it appears a new lesion,known as herpes zoster or shingles ,which affects the skin of the corresponding dermatome of the sensory nerve .
Folliculitis is an acute inflammation of one or more hair follicles or perifollicular skin.It can affect both men and women at any age ,though it is more prevalent among adults.Most cases result from an invasion of the hair follicles by Staphylococcus aureus.It commonly occurs on the scalp ,beard,limbs,axillas and pubis .Lesions consist of one or more yellowish pustules usually surrounded by an erythematous area.They are 1 to 3 mm in diameter and a hair can grow through them .
Furunculosis is a condition involving the entire hair follicle and results from an infection by Staphylococcus aureus .
Since it occurs in the hair follicles ,most commonly affected areas include the axillas ,neck and buttocks.
Furunclosis usually presents with a single lesion. It begins as a tender red inflammatory nodule which gets bigger and subsequently becomes fluctuant.
Eventually ,it develops a central area of necrosis that results in a weakened interface through which,over a few days ,purulent content exudes .
Onychomycosis or tinea unguis is a fungal infection that affects the nail unit.This condition has different clinical presentations.The most frequent subtype is distal subungual onychomycosis which typically presents subungual hyperkeratosis .
Trichophyton rubrum is the most common pathogen in this subtype.T.rubrum or T.mentagrophytes are common pathogens of proximal subungual infection in the feet .
There is another subtype in which the fungus invades directly the surface of the nail plate.
This type is known as white superficial onychomycosis .