Topic Overview

Arthropods Overview

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General Characteristics

Arthropods are ancient, highly diverse organisms with the following features:

• Segmented bodies

• Paired, jointed appendages (legs and antennae)

• Exoskeleton

• Bilateral symmetry

Life Cycle

• Growth occurs via molting through stages:

  • Egg

  • Larva or nymph

  • Adult

• Represent the most diverse phylum, with most species in:

  • Class Insecta

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Classification

1. Mandibulates (with antennae)

• Insects

• Chilopoda (centipedes)

• Diplopoda (millipedes)

2. Chelicerates (without antennae)

• Scorpions

• Spiders

• Mites

 

 

 

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Pathophysiology

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1. Mechanical Trauma

• Occurs due to:

  • Puncture or laceration during skin penetration

• Depends on mouthparts

Blood-feeding Types

• Vessel feeders:

  • Mosquitoes

  • Lice
    → Direct capillary feeding

• Pool feeders:

  • Stable flies
    → Tear skin and feed on pooled blood

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2. Injection of Substances

• Injected during feeding or stinging:

  • Irritants

  • Cytotoxic agents

  • Pharmacologically active substances (histamine, enzymes)

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3. Injection of Allergens

• Host immune response to:

  • Salivary proteins

  • Venom antigens

• Leads to:

  • Papular hypersensitivity

  • Systemic allergic reactions

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4. Secondary Infection

• Due to:

  • Scratching

  • Direct inoculation of bacteria

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5. Tissue Invasion

• Certain arthropods (e.g., flies) cause:

  • Myiasis (larval invasion of tissues)

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6. Contact Reactions

• Caused by:

  • Secretions

  • Body fragments

• May be:

  • Irritant

  • Allergic

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7. Reactions to Retained Mouthparts

• Example:

  • Tick bites

• Can lead to:

  • Granulomatous inflammation

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8. Transmission of Diseases

• Arthropods act as vectors for major diseases:

• Mosquitoes → Malaria

• Lice → Typhus

• Sandflies → Leishmaniasis

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9. Environmental and Social Factors

• Exposure influenced by:

  • Habitat

  • Clothing

  • Occupation

  • Animal contact

• Increased risk with:

  • Overcrowding

  • Poor housing conditions

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Clinical Features

• Spectrum ranges from:

  • Asymptomatic bites

  • Pruritic papules

  • Urticarial wheals

• Severe reactions:

  • Bullous lesions

  • Localized necrosis

  • Systemic hypersensitivity

 

 

 

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Investigations

• Based on identification of arthropod source

Methods

• Examination of:

  • Skin lesions

  • Environment

• Collection of specimens from:

  • Animals

  • Bedding

  • Household surroundings

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Management

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1. Prevention

• Insect repellents:

  • DEET

  • Citronella

• Protective measures:

  • Protective clothing

  • Insecticide-treated nets

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2. Treatment

• Local care:

  • Wound cleaning

  • Removal of retained parts

• Medications:

  • Topical corticosteroids

  • Antihistamines

  • Systemic therapy (if severe)

• Antibiotics:

  • For secondary infection

• Specific therapy:

  • Antivenom (if envenomation)

  • Tetanus prophylaxis when indicated

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3. Supportive Measures

• Pain relief:

  • Ice packs

  • Analgesics

• Allergy management:

  • Desensitization therapy (in selected cases)

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Key Takeaways

✔ Arthropods are diverse organisms with medical importance
✔ Cause disease via bites, stings, allergens, and infection transmission
✔ Reactions range from mild papules to severe systemic responses
✔ Prevention (repellents, nets) is crucial
✔ Treatment includes symptomatic care, antibiotics, and antivenom when needed

 

 

 

 

Arthropod-Related Skin Disorders – Clinical Features, Investigations, and Management

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Clinical Features

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Local Reactions

• At the bite/sting site:

  • Redness

  • Swelling

  • Pain

• Skin lesions:

  • Papules

  • Wheals

  • Vesicles

  • Bullae

• Varies depending on:

  • Type of arthropod

  • Host immune response

 

 

 

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Systemic Reactions

• Allergic manifestations:

  • Urticaria

  • Angioedema

  • Anaphylaxis (severe cases)

• Vector-borne disease features:

  • Fever

  • Rash

  • Organ-specific symptoms

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Chronic Manifestations

• Persistent:

  • Pruritus

  • Granulomas

  • Ulcers

  • Necrotic lesions

• Secondary bacterial infection:

  • Cellulitis

  • Abscess formation

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Special Features (Arthropod-Specific)

Ticks

• Local pruritus

• Retained mouthparts

• Erythema migrans (Lyme disease)

Mites

• Burrows

• Intense itching (scabies)

Flies

• Myiasis:

  • Larval invasion of tissues

 

 

 

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Investigations

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1. History and Clinical Examination

• Identify:

  • Arthropod exposure

  • Environmental risk factors

  • Symptom pattern

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2. Specimen Collection

• Examine:

  • Arthropods or fragments from:

    • Skin

    • Clothing

    • Bedding

    • Surroundings

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3. Histopathology

• Skin biopsy may show:

  • Arthropod parts

  • Characteristic inflammatory patterns

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4. Microbiological Tests

• Culture:

  • Detect secondary bacterial infection

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5. Serological Tests

• For vector-borne diseases:

  • Lyme disease

  • Malaria

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6. Imaging

• Useful in:

  • Myiasis

  • To locate larvae within tissues

 

 

 

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Management

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General Management

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1. Wound Care

• Clean with:

  • Antiseptics

• Remove:

  • Retained mouthparts

  • Arthropod remnants

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2. Symptomatic Relief

• Cold compresses → reduce swelling

• Antihistamines → relieve pruritus

• Corticosteroids:

  • Topical (mild–moderate)

  • Systemic (severe cases)

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3. Treatment of Secondary Infection

• Topical or oral antibiotics

• For:

  • Cellulitis

  • Abscess

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Specific Treatment

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1. Envenomation

• Antivenom:

  • Severe snake or spider bites

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2. Larval Removal (Myiasis)

• Manual extraction

• Occlusion techniques:

  • Petroleum jelly

  • Topical agents
    → Suffocate larvae before removal

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3. Treatment of Vector-Borne Diseases

• Based on causative organism:

  • Antimalarials

  • Antibiotics

  • Antivirals

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Prevention

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Insect Repellents

1. Chemical Repellents

• DEET (N,N-diethyl-meta-toluamide)

• Picaridin

• IR3535

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2. Natural Repellents

• Citronella oil

• Eucalyptus oil

• Neem oil (less effective)

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3. Usage Guidelines

• Apply to:

  • Exposed skin

  • Clothing

• Avoid:

  • Damaged skin

  • Eyes and mouth

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General Prevention

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1. Protective Measures

• Wear:

  • Long sleeves

  • Full-length clothing

• Use:

  • Insecticide-treated nets (especially in malaria-endemic areas)

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2. Environmental Control

• Eliminate:

  • Standing water (mosquito breeding)

• Maintain:

  • Clean surroundings

  • Use of pesticides

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3. Public Awareness

• Education on:

  • Arthropod risks

  • Preventive strategies

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Key Takeaways

✔ Arthropod reactions range from local papules to systemic anaphylaxis
✔ Chronic cases may lead to granulomas, ulcers, or infections
✔ Diagnosis relies on history + identification of arthropod source
✔ Management includes symptomatic care, infection control, and specific therapy
✔ Prevention (repellents, clothing, environmental control) is essential