Surreal illustration of a rainforest with a hidden eye, symbolizing Loiasis risk.

Loiasis Risk Decoded: How Forest Exposure and Itching Hold the Key

Avery Sinclair in Health & Wellness December 2025 • 4 min read.

"New research unveils a simple, effective strategy for pinpointing loiasis risk in Central and West Africa, using everyday behaviors as indicators."

Loiasis, also known as African eye worm, is a parasitic disease prevalent in the rain-forested regions of Central and West Africa. Transmitted through the bite of infected Chrysops flies, loiasis can cause a range of symptoms, from skin swelling (Calabar swellings) to the unsettling experience of seeing a worm migrate across the eye. While not typically fatal, loiasis poses significant challenges, especially in areas where mass drug administration programs for other diseases like onchocerciasis (river blindness) are underway.

Ivermectin, a drug commonly used to treat onchocerciasis, can lead to severe and potentially fatal encephalopathy (brain disease) in individuals with high levels of Loa loa microfilariae (larval worms) in their blood. This risk has led to the exclusion of many communities with high loiasis burdens from vital onchocerciasis control programs, creating a critical gap in healthcare coverage. The challenge lies in identifying these high-risk communities quickly and efficiently, especially in resource-limited settings.

Now, a new study published in the Journal of Global Health offers a promising solution. Researchers have developed diagnostic scores based on easily obtainable clinical and behavioral predictors that can help identify sub-groups at higher risk of loiasis within these communities. This innovative approach could revolutionize how loiasis is managed and controlled, ensuring safer and more effective delivery of essential medications.

Decoding Loiasis Risk: Forest Exposure and Pruritus as Key Indicators

Surreal illustration of a rainforest with a hidden eye, symbolizing Loiasis risk.

The study, conducted in the province of la Ngounié, Gabon, involved a cross-sectional survey of 947 participants of all ages. Researchers collected data through questionnaire-based interviews, focusing on clinical parameters (like the presence of itching) and behavioral exposure factors, primarily related to forest activities. Blood samples were also analyzed to detect the presence of Loa loa parasites. By analyzing this data, the researchers aimed to identify key predictors of loiasis and develop diagnostic scores that could be used in the field.

The results revealed a strong correlation between forest exposure and loiasis risk. The more frequent and intense the exposure, the higher the risk. Specifically, the study found:

Occasional forest exposure (twice per week) increased the odds of loiasis by 5.1 times.
Frequent forest exposure (daily activities) increased the odds by 11.1 times.
Intensive forest exposure (daily exposure to deep tropical rainforest) increased the odds by a staggering 25.7 times.

In addition to forest exposure, recurrent pruritus (itching) was also identified as a significant predictor. Individuals with loiasis were 7.7 times more likely to report recurrent pruritus than those without the infection. The combination of regular daily exposure to the deep rainforest and recurrent pruritus was particularly telling, increasing the likelihood of loiasis by nine-fold.

A Simpler, Safer Path to Loiasis Control

These findings have significant implications for loiasis control and onchocerciasis treatment programs. The diagnostic scores developed in this study provide a simple and rapid tool for identifying individuals at high and low risk of loiasis. This allows for more targeted interventions, ensuring that those who need treatment receive it while minimizing the risk of adverse events from ivermectin. By tailoring the delivery of ivermectin mass drug administration based on these risk scores, policymakers can create safer and more effective programs, protecting vulnerable populations from both onchocerciasis and the dangers of untreated loiasis.

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This article is based on research published under:

DOI-LINK: 10.7189/jogh.08.010413, Alternate LINK

Title: Behavioural And Clinical Predictors For Loiasis

Subject: Public Health, Environmental and Occupational Health

Journal: Journal of Global Health

Publisher: International Global Health Society

Authors: Johannes Mischlinger, Luzia Veletzky, Gildas B Tazemda-Kuitsouc, Paul Pitzinger, Pierre B Matsegui, Markus Gmeiner, Heimo Lagler, Tamirat Gebru, Jana Held, Benjamin Mordmüller, Michael Ramharter

Published: 2018-02-27

Everything You Need To Know

What is Loiasis?

Loiasis, often referred to as African eye worm, is a parasitic disease common in the rain-forested regions of Central and West Africa. It is transmitted through the bite of infected Chrysops flies. Symptoms can include skin swelling, known as Calabar swellings, and the disturbing experience of a worm moving across the eye. While usually not fatal, Loiasis presents notable challenges, particularly in areas where mass drug administration programs are in place for diseases like onchocerciasis.

How does forest exposure relate to the risk of Loiasis?

Forest exposure is a key indicator of Loiasis risk, as demonstrated by a study in la Ngounié, Gabon. The study found a strong correlation between the frequency and intensity of forest exposure and the likelihood of contracting Loiasis. Occasional exposure, frequent exposure, and intensive forest exposure significantly increased the odds of Loiasis. Therefore, understanding the level of forest exposure, such as daily activities in deep tropical rainforests, is crucial in assessing Loiasis risk within a community.

What is the significance of recurrent pruritus in the context of Loiasis?

Recurrent pruritus, or itching, is another significant predictor of Loiasis. Individuals with Loiasis were far more likely to report experiencing recurrent pruritus compared to those without the infection. The combination of regular daily exposure to the deep rainforest and recurrent pruritus dramatically increased the likelihood of Loiasis. This highlights the importance of considering both behavioral and clinical factors when assessing the risk of Loiasis.

How can the diagnostic scores help with Loiasis control programs?

The diagnostic scores developed in the study allow for the identification of individuals at high and low risk of Loiasis. This is particularly important in areas where mass drug administration of ivermectin is used to treat onchocerciasis. Ivermectin can cause severe complications, including encephalopathy, in individuals with high levels of Loa loa microfilariae. By using these risk scores, healthcare providers can tailor interventions, ensuring that those at high risk of adverse events from ivermectin are identified and managed appropriately, therefore making the delivery of essential medications safer and more effective.

What are the implications of this new research for treatment programs?

This approach ensures the safer and more effective delivery of essential medications for both onchocerciasis and Loiasis. By identifying high-risk communities and individuals, healthcare programs can prevent adverse reactions to ivermectin while still providing treatment for onchocerciasis. This targeted approach protects vulnerable populations, helping policymakers create more effective and safer programs. This also ensures that those who need treatment for Loiasis can receive it without the risk of severe complications from the medication used to treat other conditions.