Loa loa filariasis (Loaiasis)

Notes
  • It is also known as calabar swellings, fugitive swelling, tropical swelling or African eye worm.
  • It is spread by deer fly or mango fly (Chrysops spp).
  • Kenya is classified as low risk country for the disease; countries with the highest prevalence of the disease include: Democratic Republic of Congo, South Sudan and the Central African Republic, extending in the South into Angola, in the East into Uganda and in the West into South Chad, Cameroon and Nigeria.
  • The size of the female worms - 40 to 70 mm x 0.5 mm, males -30 to 34 x 0.35 to 0.43mm. Size of microfilariae - 250 to 300 μm x 6 to 8 μm. Global prevalence - 3 to13 million (mainly in Central and West Africa rain forest). Life-span of the worm – up to 17yrs.
  1. Transmission
  • Life cycle;

_An infected deer fly , Chrysops spp, bites a healthy person.

_Infective L3 larvae are enter into the skin

_Larvae develop into adult worms in the subcutaneous tissue.

_Female worms produce microfilariae

_Microfilariae may migrate to the spinal cord, urine, sputum, lungs and peripheral blood vessels.

_In the deer fly microfilariae shed the sheath, migrate into midgut and then to thoracic muscles.

_ Microfilariae develop into L1 larvae then L3 larvae.

_L3 larvae migrate into deerfy proboscis and are innoculated into human host during the feeding of deer fly.

Symptoms
  • Lymphedema
  • Sometimes asymptomatic
  • Visible subconjunctival migration of an adult worm to the eyes
  • Episodic angioedema (Calabar swellings) in the arms and legs
  • Ocassionally pruritis
  • Urticaria
  • Painful cyst-like swellings on the connective tissues.
  • Eosinophilia (key characteristic of filarial infection).
  • Chronic abscesses and consequent granulomatous reactions and fibrosis (caused by dead worms).
Diagnosis
  • Physical examination (Calabar swelling)
  • Microscopic examination of blood for microfilariae (the best time to take the sample is 10 am and 2 pm) but 33% of cases are amicrofilaremic.
  • Immunoassay (antigen detection).
  • Slit-lamp examination of the cornea and anterior chamber of the eye (microfilariae may be visible)
  • Molecular diagnostics (DNA PCR)
Management
  • Symptomatic loiasis and < 8000 microfilariae/mL blood

Rx: Tabs Diethylcarbamazine (DEC) 50 mg on day 1, 50mg TID on day 2, 100mg TID on day 3, then 2.7 to 3.3 mg/kg TID x 3/52.

NB: DEC worsens proteinuria and when there is intense infection encephalopathy may occur leading to coma and death.

  • Patients with > 8000 microfilariae/mL blood are at risk of encephalopathy

Rx:

Initial treatment with albendazole 200mg BD x 3/52 to reduce the microfilarial load to < 8000/ mL before DEC is initiated.

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