Infestation is defined as the harbouring of insect or worm parasites in or on the body. Worms—on or in the skin—are infrequent except in tropical countries. Insect life on the skin is usually transient in temperate climes, although a mite…
Infections constitute one of the biggest problems in dermatology in tropical countries of the developing world. However, tropical infections may also be seen in countries in which they are non-endemic—among visitors and immigrants, or when acquired abroad by the indigenous…
Yeasts such as Malassezia and Candida albicans exist as commensals and form a normal part of the skin microbiome, where they cause minimal inflammation in the skin. Other fungi such as dermatophytes actively digest keratin and induce significant inflammation (…
Fungal infection in humans is common and mainly due to two groups of fungi: ● Dermatophytes : multicellular filaments or hyphae ● Yeasts : unicellular forms that replicate by budding. These are usually confined to the stratum corneum, but deep…
Immunodeficiency results from absence or failure of one or more elements of the immune system. It may be acquired, e.g. acquired immune deficiency syndrome (AIDS), or inherited, e.g. chronic mucocutaneous candidiasis. Human immunodeficiency virus disease Infection with HIV is a…
Herpes simplex Herpes simplex is a very common, acute, self-limiting vesicular eruption due to infection with Herpesvirus hominis . Aetiopathogenesis and pathology Herpes simplex virus is highly contagious and is spread by direct contact with infected individuals. The virus penetrates…
Unlike bacteria and yeasts, viruses are not thought to exist on the skin surface as commensals. However, studies in patients with viral warts have shown viral DNA in epidermal cells of seemingly normal skin next to warty areas. Viral warts…
Diseases due to commensal overgrowth Sometimes, ‘normal’ commensals can result in disease. Among the most common are the following: ● Pitted keratolysis . Overgrowth of resident microorganisms that digest keratin; occurs with occluding footwear and sweaty feet ( Fig. 28.1…
The skin is a barrier to infection but, if its defences are penetrated or broken down, numerous microorganisms can cause disease ( Table 27.1 ). Table 27.1 Bacterial diseases of the skin Organism Infection Commensals Erythrasma, pitted keratolysis, trichomycosis axillaris…
Photodermatoses—idiopathic Polymorphic light eruption Polymorphic light eruption is often incorrectly referred to as ‘prickly heat’ (a different condition) and is characterized by pruritic papules, plaques and sometimes vesicles that last for days in light-exposed areas. Clinical presentation This is the…