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INTRODUCTION TO CHAPTER

Arthropods have always feasted on humans and humans have tried countless strategies to keep them from doing so. Although seldom causing any life-threatening physical illness, the societal burden of biting and sucking bugs is significant, costing millions of dollars, tremendous discomfort, and immeasurable emotional distress. They bite, we itch, we scratch, and these facts seem destined to endure.

SCABIES

Introduction

Table Key Points for Scabies

  • ✓ Scabies is transmitted from person to person by direct skin contact.

  • ✓ Scabies typically presents with intensely pruritic, excoriated papules on the hands, wrists, arms, trunk and genitals. The head, neck and feet may be affected in children.

  • ✓ A burrow, a short, wavy line, is pathognomic of scabies.

  • ✓ Permethrin 5% cream is considered the first line treatment for scabies.

  • ✓ Patients should be advised that it may take up to 4 to 6 weeks for symptoms to resolve despite effective treatment.

Scabies is a common parasitic infection caused by the mite Sarcoptes scabiei var hominis. Transmission of the mite is primarily person-to-person by direct skin contact. Situations that result in more skin-to-skin contact, such as parents with small children, sexual activity, overcrowding, and institutional settings increase the prevalence of infestation. Although the scabies mite has not been shown to transmit any significant pathogens, the intense itching associated with the infestation, the risk of superinfection of excoriated skin and the fact that up to 300 million people may be affected worldwide annually makes scabies a significant public health problem.1

Pathogenesis

Sarcoptes scabiei is an obligate human parasite that completes its entire 30-day life cycle within the epidermis. The fertilized female weaves through the epidermis and leaves a trail of 60–90 eggs and feces (scybala), in her burrow (Figure 14-1). The eggs hatch into larvae which then mature into nymphs and adults. The rash and pruritus of scabies is a result of a hypersensitivity reaction to the mite and its detritus.

Figure 14-1.

Burrow in a finger web: Thin curved ridge in the superficial epidermis created by a female mite.

The incubation period from infestation to pruritus can range from days to months. The first time an individual is infested it typically takes 2–6 weeks to become sensitized and develop symptoms, but in subsequent infestations, the previously hypersensitized individual can begin itching in as little as 1–3 days. Some infested individuals never develop hypersensitivity to the mite and never experience symptoms but can still transmit the infection; these are asymptomatic "carriers."

Clinical Presentation

History

Intense pruritus is the main presenting complaint, although very young children who can't verbalize itching are often irritable and eat ...

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