Drugs that target early stages of Onchocerca volvulus: A revisited means to facilitate the elimination goals for onchocerciasis.

Several issues have been identified with the current programs for the elimination of onchocerciasis that target only transmission by using mass drug administration (MDA) of the drug ivermectin. Alternative and/or complementary treatment regimens as part of a more comprehensive strategy to eliminate onchocerciasis are needed. We posit that the addition of "prophylactic" drugs or therapeutic drugs that can be utilized in a prophylactic strategy to the toolbox of present microfilaricidal drugs and/or future macrofilaricidal treatment regimens will not only improve the chances of meeting the elimination goals but may hasten the time to elimination and also will support achieving a sustained elimination of onchocerciasis. These "prophylactic" drugs will target the infective third- (L3) and fourth-stage (L4) larvae of Onchocerca volvulus and consequently prevent the establishment of new infections not only in uninfected individuals but also in already infected individuals and thus reduce the overall adult worm burden and transmission. Importantly, an effective prophylactic treatment regimen can utilize drugs that are already part of the onchocerciasis elimination program (ivermectin), those being considered for MDA (moxidectin), and/or the potential macrofilaricidal drugs (oxfendazole and emodepside) currently under clinical development. Prophylaxis of onchocerciasis is not a new concept. We present new data showing that these drugs can inhibit L3 molting and/or inhibit motility of L4 at IC50 and IC90 that are covered by the concentration of these drugs in plasma based on the corresponding pharmacological profiles obtained in human clinical trials when these drugs were tested using various doses for the therapeutic treatments of various helminth infections.