Decades of veterinary research may supply ammunition for the ongoing war against worms in global health.
Hookworms, roundworms, whipworms and other varieties of soil-transmitted helminths (STH) compromise the health and vigor of more than 1.2 billion people worldwide. Although these are among the world’s the most common pathogens, global investment in their study and control lags other categories of infectious disease.
“Most health control efforts in the developing world are targeted at diseases which are lethal — HIV, Malaria, TB,” said Tim Geary, director of the institute of parasitology at McGill University. These high-profile diseases “have already or may end up on our shores, so there’s an increased awareness and concern about them.”
Although STH draws less attention than other diseases, interest in combatting the worms is growing, and with that so are fears of the parasites developing resistance to the drugs used to fight them. Geary chaired a strategy session on this topic during the 2016 COR-NTD conference in Atlanta.
Worm infection saps energy, impairs learning in children and working capacity in adults, and diminishes physical and mental performance in all life activities. This holds back the economic development of communities and contributes to the cycle of poverty and malnutrition, Geary said.
Luckily, anthelmintics, a class of drugs used to combat STH, are safe, cheap and effective. They were first developed for use in animals and are mainstays for treating parasites in livestock and pets, putting veterinary research in worm control ahead of equivalent research in humans.
But experts fear the worms will develop resistance to the drugs in people, a problem that plagues veterinary medicine.
“For the moment, the good news is, we don’t think resistance is an issue,” said parasitologist Jozef Vercruysse, an emeritus professor at Belgium’s Ghent University who shared his more than 40 years of experience during the session. “However, one day it will be a problem, and we should be ready.”
Geary said that the battle against STH illustrates the need to pursue the “One Health” concept, which holds that the health of humans, animals and the environment is all connected and that research in one area can help the others.
“There’s a huge amount of experience in the deployment of anthelmintic medication to improve the health of animals, both companion and livestock, and enormous experience in the development and spread of resistance to those medicines,” Geary said. “Those lessons are often not translated to the human side.”
Selection for drug resistance in intestinal parasites is complicated because worm species are genetically diverse, have enormous population sizes and high mutation rates, according to Ray Kaplan, infectious disease professor in the University of Georgia’s College of Veterinary Medicine. This problem is compounded by the paucity of funding for veterinary research compared with medical research.
Kaplan and Vercruysse both said better monitoring is essential as the threat of resistance in humans looms with no real solution in sight.
“If we wait for drug resistance to develop in humans, it will be too late,” Kaplan said, adding that drug developers are already outpaced by “completely out of control” resistance in livestock.
“It seems irrational and irresponsible to assume that [resistance] is not going to happen,” he said. “We should go forward with the assumption that it’s going to happen, because we have so much evidence of that.”
While soil-transmitted helminths used to be a major problem in North America, particularly in the South, improvements in water and sewage stopped their spread. Today these parasites flourish in the developing world, where better sanitation is as important in reining them in as mass drug administration.
“Without sanitation, we will be giving drugs away for the rest of our lives,” Geary said. Another problem is that public health campaigns often give only one dose of anthelmintics to people in hard-to-reach areas, even though evidence shows that several consecutive days of treatment is more effective.
“One of my pet peeves is that we tend to treat animals in the West better than we treat people in Africa or in developing countries,” Geary said. “We don’t trust people to be able to contribute to their own health care by administering several doses without supervision, which is a huge mistake.”