Loa

• Loa loa

  Means "Worm worm"

  
• Loa loa

  • Common name: African Eye Worm
  • Worm can be seen and extracted from the eye, hence the name

  
• Vectors

  • Chrysops fly
  • Deer fly
  • Horse fly
  • Mango fly
  • Day-biting flies
• Infective Stage

  Third stage larvae (L3)
• Diagnostic Stage

  • Microfilaria in spinal fluid, urine, CSF, PBS, Lungs
  • Adult in subcutaneous biopsy
• Habitat

  Subcutaneous tissue: affects conjunctiva of the eye

  
• Loa loa is found in West Africa and Ethiopia
• Adult Loa loa

  • Commonly found in the subcutaneous tissue
  • Male: 30 – 34 mm by 0.35 – 0.43 mm
  • Female: 40 – 70 mm by 0.5 mm
  • Irregular bumps typical of adult Loa loa
• Microfilaria of Loa loa

  • Measurement: 250 – 300 um by 6 – 8 um
  • Sheathed
  • Tail is tapered with nuclei extending to the tip
  • Diurnal periodicity: Day - blood, Night - spinal fluids, urine, sputum
  • Non-circulating phase: Lungs
• Life cycle of Loa loa

  1. Vector: Chrysops – introduces L3 to humans upon biting

  2. L3 matures to become adult male and female in the subcutaneous tissue, copulates, and female gives birth to microfilariae. During the day, the microfilaria goes to the circulation. Chrysops fly is a day-biter and would then be infected by the microfilariae in the blood. Inside the vector, the microfilariae molts to become L1, L2, and L3 which migrates to the head and proboscis. When the vector feeds, they infect humans with L3 and the cycle continues

  
• Calabar Swelling


  • Localized, non-tender, episodic itchy swelling or subcutaneous edema found on arms, legs, near joints
• Eye worm


  • Visible movement of the adult worm across the surface of the eye; cause congestion, itching, pain, and light sensitivity but little damage
  • More of a mechanical disturbance
• Generalized Pruritis


  • In the absence of Calabar swelling
• Lungs

  • Fluid collection
  • Lung inflammation
• Diurnal Periodicity of Loa loa microfilia


  • Daytime (10 am to 2 pm) - Peripheral blood, Best time to collect blood
  • Non-circulation phase: Lungs - Most of the time
• Identification of adult worm

  In the subconjunctivae or under the skin

  
• Diethylcarbamazine (DEC)


  • Drug of choice: Kill both microfilariae and adult, quicker resolution
  • Effective against microfilariae and adult worms
• Albendazole

  • May be given if DEC is not effective after repeated treatment
  • Slow response
• Doxycycline has no role as there is no Wolbachia in Loa loa
• Brain swelling resulting to coma and/or death

  • Adverse event after DEC treatment if with heavy infection in the brain
  • Simultaneous administration of antihistamine and steroids
• Surgical removal of migrating adult worm

  • Not curative, only for aesthetic purposes
  • May not be necessary since it is not curative - worms only cause minimal damage to the eye. Surgical removal relieves mechanical discomfort
• Prevention and Control

  1. May take weekly DEC 300 mg if visiting endemic area

  2. Use insect repellant

  3. Use clothing that covers most of the skin