An Integrated District Mapping Strategy for Loiasis to Enable Safe Mass Treatment for Onchocerciasis in Gabon

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  • 1 Programme de Lutte Contre les Maladies Parasitaires, Ministère de la Santé du Gabon, Libreville, Gabon;
  • | 2 FHI 360, Washington, District of Columbia;
  • | 3 Neglected Tropical Diseases Support Center, Task Force for Global Health, Decatur, Georgia;
  • | 4 CHICAS Research Group, Lancaster Medical School, Lancaster University, Bailrigg, Lancaster, United Kingdom;
  • | 5 Drugs and Diagnostics for Tropical Diseases, San Diego, California

The lack of a WHO-recommended strategy for onchocerciasis treatment with ivermectin in hypo-endemic areas co-endemic with loiasis is an impediment to global onchocerciasis elimination. New loiasis diagnostics (LoaScope; Loa antibody rapid test) and risk prediction tools may enable safe mass treatment decisions in co-endemic areas. In 2017–2018, an integrated mapping strategy for onchocerciasis, lymphatic filariasis (LF), and loiasis, aimed at enabling safe ivermectin treatment decisions, was piloted in Gabon. Three ivermectin-naïve departments suspected to be hypo-endemic were selected and up to 100 adults per village across 30 villages in each of the three departments underwent testing for indicators of onchocerciasis, LF, and loiasis. An additional 67 communities in five adjoining departments were tested for loiasis to extend the prevalence and intensity predictions and possibly expand the boundaries of areas deemed safe for ivermectin treatment. Integrated testing in the three departments revealed within-department heterogeneity for all the three diseases, highlighting the value of a mapping approach that relies on cluster-based sampling rather than sentinel sites. These results suggest that safe mass treatment of onchocerciasis may be possible at the subdepartment level, even in departments where loiasis is present. Beyond valuable epidemiologic data, the study generated insight into the performance of various diagnostics and the feasibility of an integrated mapping approach utilizing new diagnostic and modeling tools. Further research should explore how programs can combine these diagnostic and risk prediction tools into a feasible programmatic strategy to enable safe treatment decisions where loiasis and onchocerciasis are co-endemic.

Author Notes

Address correspondence to Katherine Gass, Neglected Tropical Diseases Support Center, Task Force for Global Health, 330 W Ponce de Leon Ave, Decatur, GA 30030. E-mail: kgass@taskforce.org

Financial support: This work received financial support from the Coalition for Operational Research on Neglected Tropical Diseases (COR-NTD), which is funded at The Task Force for Global Health primarily by the Bill & Melinda Gates Foundation, by the United Kingdom aid from the British government, and by the United States Agency for International Development through its Neglected Tropical Diseases Program.

Disclosures: M. B. is a full-time employee of Drugs and Diagnostics for Tropical Diseases, the company that manufactures the Loa Antibody Rapid Test.

Authors’ addresses: Sylvie Ntsame Ella and Julienne Atsame, Programme de Lutte Contre les Maladies Parasitaires, Ministère de la Santé du Gabon, Libreville, Gabon, E-mails: sntsameella@gmail.com and julienneatsame@yahoo.fr. Kisito Ogoussan, FHI 360, Washington, DC, E-mail: kogoussan@fhi360.org. Katherine Gass and Lee Hundley, Neglected Tropical Diseases Support Center, Task Force for Global Health, Decatur, GA, E-mails: kgass@taskforce.org and lhundley@taskforce.org. Peter J. Diggle and Olatunji Johnson, CHICAS Research Group, Lancaster Medical School, Lancaster University, Bailrigg, Lancaster, United Kingdom, E-mails: p.diggle@lancaster.ac.uk and o.johnson@lancaster.ac.uk. Marco Biamonte, Drugs and Diagnostics for Tropical Diseases, San Diego, CA, E-mail: marco.biamonte@ddtd.org

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