Loa loa

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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.

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Loa loa

Loaiasis refers to the symptoms that occur when a human is infected with the parasite, Loa loa. Loaiasis synonyms include:
  • African eye worm
  • Loaina
  • Filaria Loa
  • Calabar swellings
  • Microfilaria diurnal
Note: Calabar swellings are the itch swellings (localized angioedema) occurring on the body once infection occurs. The name Calabar comes from the name of a Nigerian town. They are thought to be a type of allergic reaction to the metabolic products of the Loa loa worms or to dead Loa loa worms.
Summary of the General Morphologic Characteristics of the Microfilariae:
Filarial AgentLengthWidthNuclear Column
Loa loaLarge (>200 μm in length)
Large species tend to be as wide as a red blood cell (RBC), about 6-8 μm in diameter
Compact (dense)
HeadspaceTailSheath on Giemsa
ShortNuclei randomly distributed to tip of tailPresent: Colorless
32. CDC/Melvin. Image #21533. "Under a magnification of 1700X, this photomicrograph revealed some of the ultrastructural features exhibited at the anterior end of a Loa loa microfilaria. In this view, you are able to see the sheath that encased the head, as well as the cephalic space contained inside." PHIL public domain. Created 1966. Accessed April 6, 2023. https://phil.cdc.gov/Details.aspx?pid=21533
33. CDC/Melvin. Image #21534. "Under a magnification of 1700X, this photomicrograph revealed some of the ultrastructural features exhibited at the posterior end of a Loa loa microfilaria. In this view, you are able to see the sheath that encased the tail region, as well as the nuclei contained inside the tail." PHIL public domain. Created 1966. Accessed April 6, 2023. https://phil.cdc.gov/Details.aspx?pid=21534

Loa loa anterior (head). Note the short headspace. Avoid confusion with the presence of a sheath by locating the headspace first. (32)
Loa loa posterior (tail). (33)