The soil-transmitted nematodes (STNs) or helminths (hookworms, whipworms, large roundworms) infect the intestines of ~1.5 billion of the poorest peoples and are leading causes of morbidity worldwide. Only one class of anthelmintic or anti-nematode drugs, the benzimidazoles, is currently used in mass drug administrations, which is a dangerous situation. New anti-nematode drugs are urgently needed. Bacillus thuringiensis crystal protein Cry5B is a powerful, promising new candidate. Drug combinations, when properly made, are ideal for treating infectious diseases. Although there are some clinical trials using drug combinations against STNs, little quantitative and systemic work has been performed to define the characteristics of these combinations in vivo.

Methodology/Principal findings

Working with the hookworm Ancylostoma ceylanicum-hamster infection system, we establish a laboratory paradigm for studying anti-nematode combinations in vivo using Cry5B and the nicotinic acetylcholine receptor (nAChR) agonists tribendimidine and pyrantel pamoate. We demonstrate that Cry5B strongly synergizes in vivo with both tribendimidine and pyrantel at specific dose ratios against hookworm infections. For example, whereas 1 mg/kg Cry5B and 1 mg/kg tribendimidine individually resulted in only a 0%-6% reduction in hookworm burdens, the combination of the two resulted in a 41% reduction (P = 0.020). Furthermore, when mixed at synergistic ratios, these combinations eradicate hookworm infections at doses where the individual doses do not. Using cyathostomin nematode parasites of horses, we find based on inhibitory concentration 50% values that a strongylid parasite population doubly resistant to nAChR agonists and benzimidazoles is more susceptible or “hypersusceptible” to Cry5B than a cyathostomin population not resistant to nAChR agonists, consistent with previous Caenhorhabditis elegans results.


Our study provides a powerful means by which anthelmintic combination therapies can be examined in vivo in the laboratory. In addition, we demonstrate that Cry5B and nAChR agonists have excellent combinatorial properties—Cry5B combined with nAChR agonists gives rise to potent cures that are predicted to be recalcitrant to the development of parasite resistance. These drug combinations highlight bright spots in new anthelmintic development for human and veterinary animal intestinal nematode infections.

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Publication Date


Notes/Citation Information

Published in PLOS Neglected Tropical Diseases, v. 12, no. 5, e0006506, p. 1-22.

© 2018 Hu et al.

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Funding Information

This project was supported by (1) the National Institutes of Health/National Institute of Allergy and Infectious Diseases grant 5R01AI056189, (2) Agriculture and Food Research Initiative Competitive Grant no. 2015-11323 from the USDA National Institute of Food and Agriculture, (3)Bill & Melinda Gates Foundation Grant no. OPP1067992, and (4) a PATH Drug Solutions Grant, all to RVA.

Related Content

Data Availability: All relevant data are within the paper and its Supporting Information files.

journal.pntd.0006506.s001.docx (445 kB)
S1 Fig. Cry5B and tribendimidine (TrBD) combination studies in vivo against hookworm infections in hamsters.

journal.pntd.0006506.s002.docx (15 kB)
S1 Table. In vivo data associated with experimental results in Figs 1, 2, 4, 5 and 7.

journal.pntd.0006506.s003.docx (16 kB)
S2 Table. In vivo data associated with experimental results in S1 Fig.

journal.pntd.0006506.s004.docx (16 kB)
S3 Table. 95% confidence limits associated with experimental results in Tables 1, 2, S1 and S2.