The field of research and development of parasiticides provides perhaps the most blatant concrete examples of the One Health approach in parasitology, spanning across human and veterinary medicine. The possibly most renowned case in point in this respect is represented by the “wonder drug” ivermectin. Discovered in the late 1970s and initially developed for veterinary use as a broad-spectrum endectocide targeting gastro-intestinal nematodes and several ectoparasitic arthropods, ivermectin has then been largely employed in human medicine for the control of onchocerciasis, lymphatic filariasis , certain soil-transmitted helminthiases and scabies . This drug still represents the mainstay of two global campaigns aiming to eliminate onchocerciasis and LF, by the means of Mass Drug Administration , made possible through donations of the active ingredient by Merck & Co., Inc.. Recently, the use of ivermectin was proposed for MDAs in both humans and livestock as a complementary strategy to control malaria mosquito vectors .
Another successful example of an anthelmintic employed in both human and veterinary medicine is that of praziquantel. Also discovered in the 1970s, it is used to control cestodes and trematodes in dogs, cats, horses and sometimes even cattle , and it represents the only currently available option for the control of schistosomiasis in humans . Over the years, praziquantel has indeed been used for MDA-based preventative chemotherapy campaigns targeting school aged children in schistosomiasis-endemic areas in Africa . However, risks of emergence and/or spreading of resistance or reduced efficacy in human parasites addressed towards ivermectin and praziquantel , together with the need for effective drugs and/or vaccines against NTDs and malaria, have paved the way for initiatives aiming to fill the void in R&D pipelines against these diseases. Indeed, from the early 2000s onwards, several “Product Development Partnerships” started being established, under the model of “Public–Private Partnerships” . These include, among others, the Drugs for Neglected Diseases initiative , Medicines for Malaria Venture and the Global Health Innovation Technology , focused on drug and/or vaccine development; the Foundation for Innovative Diagnostics devoted to diagnostics; the Program for Appropriate Technology in Health dedicated to vaccine R&D, primary health care and advocacy; and the Innovative Vector Control Consortium , developing vector control tools .
Such PDPs are non-profit entities that collaborate with human pharmaceutical and biotech firms to support them in the development of solutions to address NTDs and malaria. Within this framework, the substantial funding provided by multilateral, bilateral and philanthropic donors , allows for the “de-risking” of R&D projects that would otherwise be prohibitive for industry alone, due to the limited return on investment that they may generate . The execution of the London Declaration on NTDs in 2012, which gathered initially the world’s 13 leading pharmaceutical companies, generated a major momentum in the fight against NTDs, catalysing an investment of more US$785 million to support R&D programmes . For example, DNDi’s target conditions include several parasitic NTDs that are endemic to the African continent such as leishmaniasis, sleeping sickness , LF and onchocerciasis . With respect to the latter condition, DNDi’s efforts are currently focused on evaluating emodepside, an anthelminthic veterinary drug used to control nematodes in cats and dogs, for the development of an oral macrofilaricidal treatment for onchocerciasis in humans, to be delivered as a tablet . Following successful Phase I studies in healthy volunteers, this project will soon undergo a Phase II proof-of-concept clinical trial in Ghana, aiming to assess the safety and efficacy of emodepside for people living with onchocerciasis . In the veterinary field, the Global Alliance for Livestock Veterinary Medicine was established in 2004 as a PDP supporting veterinary pharmaceutical companies developing drugs, vaccines and diagnostic tools for livestock diseases of poor smallholder farmers in sub-Saharan Africa and South Asia .
Some of GALVmed’s target diseases include NZDs such as porcine cysticercosis and animalAfrican trypanosomiasis and the zoonotic arthropod-borne RVF . In the case of porcine cysticercosis, GALVmed bolstered the commercial development of a dual approach based on the fifirst licensed cysticercosis vaccine for pigs , administered concurrently with a therapeutic drug , used to eliminate parasitic larvae, according to a “therapeutic-prevention” strategy . Following successful trials in Nepal, Tanzania, Uganda and Zambia, both products are now undergoing registration in several African countries . Given the zoonotic nature of cysticercosis, this initiative is expected to bring also public health benefits to the communities administering these products to their pigs. The examples of dewormers such as ivermectin and praziquantel show that opportunities do exist with regards to translating or even “repurposing5” drug discovery and development from human to veterinary health applications, and vice versa, in the area of parasitic infections.