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Understanding Loiasis (African Eye Worm)

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Loiasis, or African eye worm, is a treatable parasitic infection caused by the Loa loa nematode and spread by fly bites in Central and West Africa. Safe treatment requires a specialist to measure your parasite load through a blood test before starting medication.

Key Takeaways

  • • Loiasis is a parasitic infection caused by the Loa loa nematode and transmitted by Chrysops flies in Central and West Africa.
  • • Seeing or feeling a worm moving under the skin or across the eye is a classic, though distressing, symptom of the infection.
  • • Accurate diagnosis often requires a specific blood test drawn between 10 AM and 2 PM to check for the parasite.
  • • Safe treatment involves determining your exact parasite load before carefully administering curative medications like DEC.

Finding a worm moving under your skin or across the surface of your eye is a deeply shocking and distressing experience [1]. It is completely normal to feel a sense of horror, anxiety, or disbelief [1]. While this condition, known as Loiasis (or African Eye Worm), can feel like something out of a nightmare, it is a well-understood medical condition that is treatable with expert care.

Historically, Loiasis was often dismissed as a “benign” or harmless nuisance [2]. However, modern medical research has debunked this myth, proving that the infection is a serious public health issue that requires careful management to prevent significant disability and health risks [3][2].

What is Loiasis?

Loiasis is a parasitic infection caused by the Loa loa nematode, a type of microscopic worm [2]. It is primarily found in the tropical equatorial rainforests of Central and West Africa—specifically in high-risk countries like Cameroon, Nigeria, Gabon, and the Democratic Republic of Congo [4][2]. It affects an estimated 10 to 20 million people worldwide [5].

How it is Transmitted

The infection is spread through the bites of Chrysops flies (commonly known as deer flies or mangrove flies) [6]. These flies:

  • Live in forest canopies and breed in muddy streams or swampy areas [6][7].
  • Are most active during the day and are attracted to movement and wood smoke [7].
  • Pass the parasite’s larvae into your skin when they bite to take a blood meal [6].

Once inside the human body, the larvae grow into adult worms that can live for up to 15 years, migrating through the connective tissues under your skin [5].

Navigating Your Care

Because treating Loiasis requires precision and safety protocols, we have broken down everything you need to know into detailed sections:

You are not alone in this. With the right medical guidance, this parasite can be safely managed and cleared from your system.

Frequently Asked Questions

What is Loiasis (African eye worm)?
Loiasis is a parasitic infection caused by the Loa loa nematode. It is transmitted through the bites of Chrysops flies, primarily in the tropical rainforests of Central and West Africa.
How do you get an African eye worm infection?
You can get the infection from the bite of an infected Chrysops fly, also known as a deer fly or mangrove fly. These flies pass the parasite's larvae into your skin when they bite to take a blood meal.
Should I get tested for Loiasis if I haven't seen a worm in my eye?
Yes, if you have lived in or traveled to high-risk areas like Cameroon, Nigeria, Gabon, or the Democratic Republic of Congo, you should be screened. Many people have the infection and experience transient skin swellings without ever seeing a worm.
What is the first step in treating Loiasis?
The most critical first step is having a doctor determine your parasite load through a specific blood test. This ensures that curative medications like DEC are used safely and effectively as part of a staged treatment plan.

Questions for Your Doctor

  • • Given my recent travel or residence history, should I be screened for Loiasis even if I haven't seen an eye worm?
  • • Can you confirm if you have experience managing parasitic infections like Loa loa, or should I be referred to an infectious disease specialist?
  • • If I am diagnosed with Loiasis, what are the first steps to determine my parasite load before considering any medication?

Questions for You

  • • Have I recently traveled to or lived in high-risk areas of Central or West Africa, such as Cameroon, Nigeria, Gabon, or the Democratic Republic of Congo?
  • • Have I experienced any unexplained, transient skin swellings or the sensation of something moving in my eye?

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References

  1. 1

    Disability and quality of life assessment using WHODAS-12 items 2.0 and EQ-5D-5L in a rural area endemic for loiasis in the Republic of Congo: A population-based cross-sectional study (the MorLo project).

    Hemilembolo MC, Campillo JT, Dupasquier V, et al.

    PLoS neglected tropical diseases 2025; (19(9)):e0013491 doi:10.1371/journal.pntd.0013491.

    PMID: 40953102
  2. 2

    The African eye worm: current understanding of the epidemiology, clinical disease, and treatment of loiasis.

    Ramharter M, Butler J, Mombo-Ngoma G, et al.

    The Lancet. Infectious diseases 2024; (24(3)):e165-e178 doi:10.1016/S1473-3099(23)00438-3.

    PMID: 37858326
  3. 3

    Burden of disease in Gabon caused by loiasis: a cross-sectional survey.

    Veletzky L, Hergeth J, Stelzl DR, et al.

    The Lancet. Infectious diseases 2020; (20(11)):1339-1346 doi:10.1016/S1473-3099(20)30256-5.

    PMID: 32585133
  4. 4

    A call for loiasis to be added to the WHO list of neglected tropical diseases.

    Jacobsen KH, Andress BC, Bhagwat EA, et al.

    The Lancet. Infectious diseases 2022; (22(10)):e299-e302 doi:10.1016/S1473-3099(22)00064-0.

    PMID: 35500592
  5. 5

    Preliminary comparison between an in-house real-time PCR vs microscopy for the diagnosis of Loa loa and Mansonella perstans.

    Formenti F, Tang TT, Tamarozzi F, et al.

    Acta tropica 2021; (216()):105838 doi:10.1016/j.actatropica.2021.105838.

    PMID: 33484727
  6. 6

    Environmental factors associated with the distribution of Loa loa vectors Chrysops spp. in Central and West Africa: seeing the forest for the trees.

    Badia-Rius X, Betts H, Molyneux DH, Kelly-Hope LA

    Parasites & vectors 2019; (12(1)):72 doi:10.1186/s13071-019-3327-9.

    PMID: 30728063
  7. 7

    Loa loa vectors Chrysops spp.: perspectives on research, distribution, bionomics, and implications for elimination of lymphatic filariasis and onchocerciasis.

    Kelly-Hope L, Paulo R, Thomas B, et al.

    Parasites & vectors 2017; (10(1)):172 doi:10.1186/s13071-017-2103-y.

    PMID: 28381279

This page provides an overview of Loiasis for informational purposes only. Always consult an infectious disease or travel medicine specialist for the diagnosis and treatment of parasitic infections.

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