African Eye Worm Threatens Efforts To Eliminate River Blindness

Efforts to eliminate river blindness, a debilitating parasitic disease that causes vision loss in 1.15 million people, may be threatened by another infection known as African eye worm, according to a modelling study published in Clinical Infectious Diseases. While the World Health Organization has set a target to eliminate river blindness in most African countries in the next five years, the study predicts that 4 million people living in areas with African eye worm will still be at risk of the blinding disease in 2025, threatening almost four decades of elimination efforts.

The study, co-authored by researchers from Erasmus MC, University Medical Center Rotterdam in the Netherlands, and the Drugs for Neglected Diseases Initiative, also predicts that 90% of these people will live in areas currently not covered by treatment programmes for river blindness.

A villager’s eyes are being examined for African eye worm by Dr Philippe Urwotho, a medical doctor and Provincial Coordinator of the DRC’s Neglected Tropical Disease National Programme.

Elimination of river blindness, also known as onchocerciasis, is mainly reliant on a strategy of “mass drug administration,” whereby entire communities living in endemic areas are given a safe and effective drug called ivermectin regularly in order to prevent the parasitic disease from progressing or spreading. Ivermectin only targets the juvenile worms that can cause blindness or severe chronic skin itching, so mass drug administration needs to be repeated for the full life span of the adult parasite – 10 to 12 years – to fully eliminate the parasite from a community.

The problem arises when communities live in areas with both the river blindness parasite and the African eye worm, or Loa loa – people who have a high number of Loa loa larvae in their blood are at risk of life-threatening complications if they receive ivermectin. As a result, ivermectin cannot be safely used in mass drug administration campaigns in areas co-endemic for both diseases, and river blindness treatment programmes in these areas have not started.

“The current approach to preventing river blindness based on mass drug administration of ivermectin has been extraordinarily successful,’ says Sabine Specht, Head of Filarial Clinical Programme at DNDi, in a press release. “But alternative treatment strategies will be needed if we want to eliminate the disease, including the development of entirely new tools that offer a rapid and safe cure for river blindness.”

The authors predict that in 2025, there will still be at least 31,000 individuals infected with onchocerciasis and unable to use ivermectin, due to the high load of  Loa loa worms in their bloodstream – as the current treatment regimens for co-infected people are not well adapted for use in the field. According to the study, there are also currently no safe medications that can be used to kill adult forms of the worms that cause river blindness. The authors highlight that the lack of existing field-friendly treatments and diagnostics for both diseases merit further R&D for both diseases.

River blindness is transmitted by the bite of infected blackflies, which live near fast-moving rivers. The disease can progress to severe itching, skin lesions, and eventual blindness. Before large-scale control campaigns began in the mid-1970s, whole villages would eventually go blind from the disease. In 2017, it was estimated that 14.6 million people infected with onchocerciasis had severe chronic itching and skin disease, and 1.15 million had vision loss.

African eye worm, or Loa loa, gets its name from its most infamous tell-tale sign: the visible passing of the Loa loa worm through the eye. While previously thought to be rather mild, recent studies show that Loa loa infection can cause severe illness such as cardiac fibrosis, encephalopathy, and neurological or psychiatric disorders.

Image Credits: DNDi.

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