In the fight against intestinal roundworms — a disease that affects over a third of the world’s population and kills 60,000 people a year — scientists at UCSD have discovered a naturally occurring treatment for intestinal roundworms that is three times more effective than the best of existing drugs.
According to Raffi Aroian of the UCSD Division of Biological Sciences, who led the study, a bacterium called Bacillus thuringiensis — or “Bt” — is three times as effective as tribendimidine, the leading chemical drug used to treat intestinal roundworms. Bt is naturally occurring in various types of caterpillars and used in a popular insecticide.
When an insect comes into contact with crops that have been sprayed with the insecticide, Bt forms crystal proteins inside the insect’s gut that attack the animal’s cellular lining, causing gut paralysis and a quick death. In roundworms, the crystal protein Cry5B — taken from Bt — interacts with invertebrate-specific membrane molecules in the roundworm’s intestine, eventually leading to destruction of the worm’s intestine.
Though Bt is toxic to insects, it is harmless to mammals because they lack the enzymes to make the destructive molecules, leading Aroian and his team, consisting of postdoctoral employee Yan Hu and graduate student Sophia Georghiou, to believe it can cure intestinal roundworms and other internal parasites.
“We took mice infected with intestinal parasites and basically mimicked the disease,” Aroian said. “We gave them this natural pathogen of roundworms called Bt… [which is] excellent at eliminating insects and not vertebrates. The logic of the experiment is this: if we have a bacterium that we know is harmless to vertebrates, instead of using it to kill insects living in plants, we said, ‘Why don’t we feed Bt to these mice infected with intestinal roundworms?’”
The bacterium proved very effective, curing all 17 mice without any side effects. However, in order to prove that this find was truly significant — and that Bt could replicate the effects of leading drugs for intestinal parasites — Aroian had to compare it with tribendimidine, the most effective drug used to treat intestinal roundworms. Tribendimidine is still being tested and is not yet available on the market.
“We gave the infected mice this protein, saw the effectiveness and we compared it in a head-to-head study to a chemical drug still in clinical trials that is known to be the best combatant against intestinal parasites, finding that Bt was about three times better,” Aroian said.
According to the scientific journal Maternal & Child Nutrition, intestinal parasites like roundworms, pinworms and whipworms affect over 2 billion people worldwide. Though ascariasis — an infection of the parasitic roundworm — exists in the United States, it is most common in countries with poor sanitation and lack of water supplies.
These parasites can live within a human’s intestines for some time before that person displays symptoms, and travel through the body, causing slow damage in the abdomen and pelvis, as well as inflammation, toxicity and pneumonia. Heavy and prolonged infestations in children have been known to cause nutritional deficiency, growth stunting and some mental retardation.
Aroian said he hopes the discovery will help reduce the number of people suffering from roundworms.
“This should be a very cheap drug to make,” Aroian said. “This is really aimed at helping some of the poorest people in the world.”
According to the George Institute of International Health report, about $720,000 was spent in 2008 to develop new drugs specifically for these parasites. With a comparable sum of funding, clinical trials for a Bt-based roundworm drug could begin soon, Aroian said.
Readers can contact Kashi Khorasani at [email protected].
