Rapid, Point-of-Care Tool for Identifying Onchocerciasis in L loa-Endemic Areas

Loa loa bacteria
Loa loa bacteria
A test-and-not-treat strategy may help areas in which loiasis is endemic and onchocerciasis is hypoendemic so that individuals who are not at risk for serious adverse events are safely given ivermectin treatment.

A test-and-not-treat strategy for onchocerciasis and lymphatic filariasis proved to be efficacious by accurately identifying patients at risk for adverse treatment events and excluding them from community-wide drug treatment, according to a study published in the New England Journal of Medicine.

Mass drug administration programs aimed at onchocerciasis (also known as river blindness) and lymphatic filariasis were halted in Central Africa after fatalities occurred in patients with Loa loa microfilariae densities >30,000 microfilariae (mf)/milliliter (ml) blood. The adverse events were attributed to eosinophil-mediated inflammation associated with the dying microfilariae. Therefore, a test-and-not-treat method was proposed to screen for individuals at risk for treatment-related death using a smartphone-based video-microscope (LoaScope).

Individuals 5 and older from 92 villages in Cameroon participated in the study and microfilariae density was determined in 16,259 persons using the LoaScope. The treatment risk threshold was 20,000 mf/ml; patients with <20,000 mf/ml received treatment with ivermectin. Ivermectin was given to 15,522 (95.5%) participants; 340 participants (2.1%) were excluded due to higher mf densities.

A total of 2818 adverse events were observed; the most common was dermatological manifestations, followed by systemic and rheumatologic manifestations. A global adverse event severity grade of 1, 2, and 3 were assigned to 88 (9.4%), 843 (90.3%), and 3 (0.3%) patients, respectively. No hospitalizations or deaths were reported.

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The results showed the practicality of a LoaScope-based test-and-not-treat approach to reintroduce community-wide treatment programs in areas in which previous efforts had been halted due to risks from adverse treatment effects. 


Kamgno J, Pion SD, Chesnais CB, et al. A test-and-not-treat strategy for onchocerciasis in Loa loa-endemic areas. N Engl J Med. 2017;377:2044-2052.