THE MERCK MANUAL: The Merck Manual of Diagnosis and Therapymultimedia


  • Loiasis
  • Loa loa life cycle.

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    Loa loa life cycle.

    1. During a blood meal, an infected Chrysops fly (a day-biting fly) transmits 3rd-stage filarial larvae onto the skin of the human host, where the larvae enter the bite wound.

    2. The larvae mature into adults in subcutaneous tissue.

    3. Adults produce sheathed microfilariae, which circulate in the blood during the day and, when not in circulation, reside in the lungs. Microfilariae may be present in spinal fluid, urine, and sputum.

    4. The fly ingests microfilariae during a blood meal.

    5. After ingestion, the microfilariae lose their sheath, penetrate the fly's midgut, and migrate to its thoracic muscles.

    6–7. There, the microfilariae go through 3 stages (L1-L3) of larval development.

    8. Larvae migrate to the fly's proboscis and can infect another human when the fly takes a blood meal.

    Image from the Centers for Disease Control and Prevention Image Library.