Life Cycle

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The page below is a sample from the LabCE course Microfilariae in Humans. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

Learn more about Microfilariae in Humans (online CE course)
Life Cycle

A biological life cycle refers to a series of changes in the life of the organism (filarial nematode).
  • In general, the life cycles (patterns) of the different filarial worms infecting humans are quite similar.
  • The human is known as the definitive host (supporting the adult or sexually reproductive form of the parasite).
  • Terminology:
    1. infective larval stage from the vector, which matures in humans to become an:
    2. adult worm, which then mates; females produce offspring known as:
    3. tiny, thread-like larvae = microfilariae (which can be ingested by the biting arthropod and begin the cycle all over again, developing into different stages of larvae).
Life Cycle (refer to the images):
  • Once transmission occurs (as mentioned on the previous page), infective larvae enter humans, growing into adult worms.
  • Depending on the specific genus/species of the nematode: The adult nematodes may live in the human lymphatic system, subcutaneous tissue, peritoneal and pleural cavities, or other locations.
  • The development of adult worms may take months. Adults may continue to reside in a human host for years.
  • Some adult worms migrate to the eyes, as in Loa loa.
  • When mating of adult filariae occurs, female nematodes release millions of microfilariae into the peripheral circulation (or surrounding skin, depending on the genus and species).
The cycle continues as an insect vector feeds on the infected human.

6. CDC DPDx. Wuchereria bancrofti life cycle. Public domain image. Last reviewed 2019. Accessed April 6, 2023. https://www.cdc.gov/dpdx/lymphaticfilariasis/index.html
7. CDC DPDx. Brugua malayi life cycle. Public domain image. Last reviewed 2019. Accessed April 6, 2023. https://www.cdc.gov/dpdx/lymphaticfilariasis/index.html

Wuchereria bancrofti Life Cycle (CDC-DPDx). (6)
Brugia malayi Life Cycle (CDC-DPDX). (7)