Campbell, together with colleagues at MDRL, subsequently chemically modified Avermectin to a new version called Ivermectin, which turned out to be even more effective against parasitic infection (Chabala et al., 1980). Ivermectin is a semisynthetic version of Avermectin B1 containing two hydrogenation modifications. Thereafter, Campbell initiated a team effort demonstrating that the Ivermectin molecule was: (1) extraordinarily potent; (2) active against many intestinal nematodes in various host species; (3) showing durable long-term activity against some extra intestinal parasites including blood-dwelling filarial microfilariae; (4) active against benzimidazole-resistant nematodes (suggesting a different mode of action); and (5) well-tolerated by the host species, suggesting a good margin of safety (Campbell et al., 1983). Inspired by these positive results from animal studies, especially for reducing dog heartworm, Campbell proposed in 1977, that the Avermectin class be tested for use