Campbell and colleagues reported unprecedented antiparasitic effects of the agent in vivo, and that the "B1a" component of the molecule was most effective as a single oral dose.
(Order of authorship in the original publication: Egerton, Oslin, Blair....Campbell.) Digital facsimile from PubMedCentral at this link.

In 2015 William C. Campbell shared half of the Nobel Prize in Physiology or Medicine with Satoshi Ōmura “for their discoveries concerning a novel therapy against infections caused by roundworm parasites.” The other half was awarded to Tu Youyou “for her discoveries concerning a novel therapy against Malaria.”

(Thanks to Juan Weiss for this reference and its interpretation.)

Abstract

"Ivermectin is the 22,23-dihydro derivative of avermectin B1, a macrocyclic lactone produced by an actinomycete, Streptomyces avermitilis. It is active at extremely low dosage against a wide variety of nematode and arthropod parasites, apparently by virtue of its action on the mediation of neurotransmission by gamma-aminobutyric acid. It is now in commercial use in various countries for the treatment and control of parasites in cattle, horses, and sheep, and is expected to become available for use in swine and dogs. Since studies with the drug in man are in a preliminary stage, it is not yet known whether ivermectin will be useful in human medicine."

In 2015 the Nobel Prize in Physiology or Medicine 2015 was divided, one half jointly to William C. Campbell and Satoshi Ōmura "for their discoveries concerning a novel therapy against infections caused by roundworm parasites," and the other half to Tu Youyou "for her discoveries concerning a novel therapy against Malaria."

(Thanks to Juan Weiss for this reference and its interpretation.)

The first chapter of this authoritative study is a very detailed historical introduction by William C. Campbell, with a comprehensive bibliography. Campbell also authored Chapter 10: Chemotherapy and Chapter 13: Epidemiology I: Modes of transmission. Chapter 14: Epidemiology II: Geographic distribution and prevalance by Charles W. Kim breaks down coverage to most countries and regions of the world.