Veterinary Researchers Study Neglected Tropical Diseases in Humans


Richard Martin, DVM, PhD, a biomedical sciences professor at Iowa State Universitys College of Veterinary Medicine, has devoted his 35-year career to studying nematode parasites. These parasites infect approximately one-quarter of the world population, producing debilitating symptoms that devastate the lives and economies of many of the worlds underdeveloped and impoverished areas.

The parasites, such as Ascaris, hookworms, and whipworms cause poor health, but the diseases are rarely fatal. These diseases have largely been ignored and are classified as Neglected Tropical Diseases or NTDs. These parasitic attackers often go unnoticed, yet the NTD diseases affect more than two billion homes worldwide.

Martin and his ISU colleague, Alan Robertson, PhD, are working to take the "neglected" out of these diseases and develop methods of treating and preventing them. Accomplishing that will have significant worldwide impact.

Martin and Robertson are using scientific techniques and drugs adapted from veterinary medicine to study the parasites that are the major cause of NTDs. They are exploring how these drugs may be used most effectively, and how to control and limit the appearance of drug resistance. The aim is to be able to treat humans prophylactically with drugs to prevent the appearance of significant disease but to be careful not to induce drug resistance. One of the problems is to identify a safe drug that can be given in a single dose without the need to correct for the weight of the person being treated. This is because of the limited skills of the individuals dispensing the drugs.

Since there are no vaccines available, the key is to develop effective treatment through mass drug administration, parallel to what is done with animals such as sheep, cattle and swine that are fed drugs to control disease. "It is a bit ironic," said Dr. Martin, "that the world can afford to treat cattle and other animals against these parasites by giving them anthelmintic drugs, but similar treatments are too expensive for some humans or arent available to them at this time. We want to find ways to protect more of the human population, the way we protect animals."

Studies have shown that worms have nervous systems and brains; they pick up light; respond to noxious stimuli such as electrical activity, and seek out different food sources. They have an organized network of nerves and muscles. Genetically they are much more complex than bacteria or viruses they are eukaryotes (multicellular organisms). "This makes worms more sophisticated and interesting than bacteria, although they have a high yuck factor," says Martin. "Their complexity has driven a lot of research in gene identification."

Its hard to think of worms as intelligent beings with a nervous system that can learn and respond appropriately to the environment, yet these parasites have a remarkable ability to adapt and over time develop drug immunity (resistance). Understanding how these parasites develop resistance and how to overcome it is the challenge Martin is addressing.

"What we are doing is excitingly relevant to humans and animals and the number of people who will benefit from our efforts is truly significant," says Martin. "We are able to get a regular supply of parasites to use in our experiments and are the only ones in the world to use our unique electrophysiological, molecular and microfluidic technology on parasites for NTD research."

Their work has the potential to affect millions of people worldwide and the societies and economies in which they live and work. Drugs for treating diseases are most often developed for use in humans, and then adapted for animal use. In this case, the need for new drug development is driven by economics and from animal use to humans. Thus drugs like ivermectin were developed for animal use and have now been adapted for human us. Martin and Robertson recently carried out the discovery biology of a novel resistance-busting drug, derquantel, which has just been introduce to the market for animal use in New Zealand and is expected to be marketed worldwide. It will be interesting to see if this drug is adapted for human use.

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