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Skin infections

Arthropods and parasites key points test

Arthropod bites may cause: #! Anaphylaxis # Atopic eczema # Smallpox #! Malaria Explanation: Arthropod bites may cause hypersensitivity reactions including anaphylaxis (especially bee stings), secondary infection and spread viral, rickettsial and parasitic diseases including malaria (mosquitoes). Papular urticaria may result in: #! Papules # Folliculitis #! Vesicles # Onychomycosis Explanation: Papular urticaria is a hypersensitivity reaction to biting insects and results in excoriated papules, umbilicated wheals, vesicles, bullae and crusted sores. Symptoms due to spider bites include: #! None #! Local pain and tissue necrosis #! Fever, delirium and abdominal pain # Constipation Explanation: Spider bites may arise painlessly but later result in painful erythematous plaques and subsequent tissue necrosis due to toxins that cause neutrophilic destruction of endothelial cells, and systemic toxicity including fever, delirium, abdominal pain and diarrhoea. Scabies has the following characteristics: # Pruritus more severe during the day than at night # Scalp dermatitis # Burrows up to 5cm in length on the fingers #! Axillary nodules Explanation: Characteristically scabies itch is more severe at night, although itch due to other causes may also appear worse at that time. Scabies does not affect the scalp, except in young babies, bedridden elderly or in Norwegian scabies where there is a defective immune and scratching response to infestation. Infestation with head lice has the following characteristics: # Ectothrix infection #! Scalp dermatitis # Burrows up to 1cm in length on the neck #! Retroauricular lymphadenopathy Explanation: Head lice cause itchy papules in the scalp which may progress to an eczematous dermatitis, secondary infection and localised lymphadenopathy. Ectothrix infection is seen in some types of tinea capitis (fungal infection of hair). Lice do not burrow but cling to hairs. Cutaneous larva migrans has the following characteristics: #! Self-healing within three months #! Tracks up to 5cm in length on the feet # Anal autoinfection # Pulmonary involvement resulting in cough and wheezing Explanation: The hookworm larvae responsible for cutaneous larva migrans travel several centimetres under the skin causing irritable 3-5mm tracks that persist for one to three months.