Skip directly to search Skip directly to A to Z list Skip directly to site content
CDC Home
For questions about DPDx, contact us
DPDx

DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/loiasis/.

Loiasis

[Loa loa]

Adult of Loa loa in the subconjunctiva of a patient.

Adult of Loa loa in the subconjunctiva of a patient.


Microfilaria of L. loa in a thin blood smear, stained with Giemsa.

Microfilaria of L. loa in a thin blood smear, stained with Giemsa.


Microfilaria of L. loa a thick blood smear from a patient from Cameroon, stained with Giemsa. Note the nuclei extending to the tip of the tail to the left of the image.

Microfilaria of L. loa a thick blood smear from a patient from Cameroon, stained with Giemsa. Note the nuclei extending to the tip of the tail to the left of the image.

Causal Agent

Loa loa, a filarid nematode commonly referred to as the African eye worm.


Life Cycle

Life cycle of Loa Loa

The vector for Loa loa filariasis are flies from two species of the genus Chrysops, C. silacea and C. dimidiata. During a blood meal, an infected fly (genus Chrysops, day-biting flies) introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound The number 1. The larvae develop into adults that commonly reside in subcutaneous tissue The number 2. The female worms measure 40 to 70 mm in length and 0.5 mm in diameter, while the males measure 30 to 34 mm in length and 0.35 to 0.43 mm in diameter. Adults produce microfilariae measuring 250 to 300 µm by 6 to 8 μm, which are sheathed and have diurnal periodicity. Microfilariae have been recovered from spinal fluids, urine, and sputum. During the day they are found in peripheral blood, but during the noncirculation phase, they are found in the lungs The number 3. The fly ingests microfilariae during a blood meal The number 4. After ingestion, the microfilariae lose their sheaths and migrate from the fly's midgut through the hemocoel to the thoracic muscles of the arthropod The number 5. There the microfilariae develop into first-stage larvae The number 6 and subsequently into third-stage infective larvae The number 7. The third-stage infective larvae migrate to the fly's proboscis The number 8 and can infect another human when the fly takes a blood meal The number 1.

Geographic Distribution

Loa loa is found in Africa.

Clinical Presentation

Loiasis is often asymptomatic. Episodic angioedema (Calabar swellings) and subconjunctival migration of an adult worm can occur.

Back to Top

 
For questions about DPDx, contact us
  • Page last reviewed November 29, 2013
  • Page last updated November 29, 2013
  • Content source: Global Health - Division of Parasitic Diseases and Malaria
  • Notice: Linking to a non-federal site does not constitute an endorsement by HHS, CDC or any of its employees of the sponsors or the information and products presented on the site.
USA.gov: The U.S. Government's Official Web PortalDepartment of Health and Human Services
Centers for Disease Control and Prevention   1600 Clifton Road Atlanta, GA 30329-4027, USA
800-CDC-INFO (800-232-4636) TTY: (888) 232-6348 - Contact CDC–INFO