Alternative treatment strategies to accelerate the elimination of onchocerciasis

Abstract

The use of alternative (or complementary) treatment strategies (ATSs) i.e. differing from annual community-directed treatment with ivermectin (CDTI) is required in some African foci to eliminate onchocerciasis by 2025. ATSs include vector control, biannual or pluriannual CDTI, better timing of CDTI, community-directed treatment with combinations of currently available anthelminthics or new drugs, and 'test-and-treat' (TNT) strategies requiring diagnosis of infection and/or contraindications to treatment for decisions on who to treat with what regimen. Two TNT strategies can be considered. Loa-first TNT, designed for loiasis-endemic areas and currently being evaluated using a rapid test (LoaScope), consists of identifying individuals with levels of Loa microfilaremia associated with a risk of post-ivermectin severe adverse events to exclude them from ivermectin treatment and in treating the rest (usually >97%) of the population safely. Oncho-first TNT consists of testing community members for onchocerciasis before giving treatment (currently ivermectin or doxycycline) to those who are infected. The choice of the ATS depends on the prevalences and intensities of infection with Onchocerca volvulus and Loa loa and on the relative cost-effectiveness of the strategies for the given epidemiological situation. Modelling can help select the optimal strategies, but field evaluations to determine the relative cost-effectiveness are urgently needed.

Figure 1.

Decision trees for tests and treatment within the two possible TNT strategies: (a) Loa-first TNT; (b) Oncho-first TNT. The sizes of the circles correspond to the approximate relative size of the population to be tested or treated at each step in a community where loiasis coexists with hypoendemic onchocerciasis.

Figure 2.

(a) Distribution of the individuals in a community where loiasis coexists with hypoendemic onchocerciasis according to their status regarding onchocerciasis (active infection or not) and their risk of developing a post-ivermectin SAE (individuals with >30,000 Loa mf/mL). (b) Treatment given (or not) to subjects in each of the four categories by TNT strategy used (Loa-first vs Oncho-first).