Infections Secondary to Insect Bites, including Lyme Disease

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

Infections secondary to insect bites refer to bacterial, viral, or parasitic infections that arise following an insect bite. Lyme disease is a specific infection caused by Borrelia burgdorferi following a tick bite.

Aetiology

  • Bacterial: cellulitis, abscess formation (Staphylococcus aureus, Streptococcus pyogenes).
  • Lyme disease: caused by Borrelia burgdorferi, transmitted by Ixodes ticks.
  • Parasitic: Leishmaniasis (sandflies), malaria (mosquitoes).
  • Viral: Dengue fever, Zika virus (mosquito-borne).

Pathophysiology

  • Bacterial entry through broken skin leads to local infection (cellulitis, abscess).
  • Tick-borne infections, such as Lyme disease, involve systemic dissemination of spirochetes.
  • Parasitic and viral infections affect immune response, causing systemic manifestations.

Risk Factors

  • Outdoor activities in endemic areas (forests, grassy fields).
  • Failure to use insect repellent or protective clothing.
  • Delayed removal of ticks.
  • Underlying immunosuppression.

Signs and Symptoms

  • Localized infection: erythema, swelling, warmth, tenderness.
  • Lyme disease stages:
    • Early: erythema migrans (bullseye rash), fever, myalgia.
    • Disseminated: multiple erythema migrans, arthritis, neurological symptoms (facial palsy, meningitis).
    • Late: chronic arthritis, encephalopathy.
  • Parasitic and viral infections: fever, rash, systemic involvement.

Investigations

  • Blood cultures: if systemic infection suspected.
  • Wound swab: if signs of secondary bacterial infection.
  • Serology for Lyme disease: ELISA followed by immunoblot.
  • PCR testing: for Borrelia in early Lyme disease.
  • Full blood count (FBC): to assess for leukocytosis.

Management

1. Local Wound Care:

  • Clean wound with antiseptic.
  • Monitor for signs of infection.

2. Antibiotic Therapy:

  • Cellulitis: flucloxacillin or clarithromycin (if penicillin allergy).
  • Lyme disease: doxycycline (first line) or amoxicillin (if pregnant or under 8 years).
  • Severe Lyme disease: IV ceftriaxone for neurological or cardiac involvement.

3. Prevention:

  • Use insect repellent (DEET based products).
  • Check for and promptly remove ticks.
  • Wear long clothing in endemic areas.

4. Referral:

  • Infectious diseases: for complicated or late-stage Lyme disease.
  • Dermatology: if persistent skin manifestations occur.
  • Neurology: for Lyme neuroborreliosis.
Infectious DiseasemypanotesInfections Secondary to Insect Bites, including Lyme Disease