Neima Briggs, sitting in her lab in New Haven, holds a petri dish containing tiny, translucent worms no thicker than a human eyelash—Nippostrongylus brasiliensis, a rodent hookworm that may hold outsized promise for human health. These parasites, part of a broader group known as helminths, infect an estimated 1.9 billion people worldwide—nearly one in four on Earth. While they can weaken vaccine responses and, in some cases, contribute to cancer, their remarkable ability to quiet the immune system is now guiding scientists toward breakthroughs in treating inflammatory diseases.
Helminths, which include tapeworms, flukes, and roundworms, range in size from barely visible 1 millimeter to astonishing lengths of up to 15 meters. They thrive in regions with poor sanitation, entering the body through contaminated food or water and taking up residence in the intestines, lungs, or gastrointestinal tract. Yet despite their prevalence, they often cause surprisingly little acute harm. Instead, they persist for years by subtly reprogramming the host’s immune system—not eliminating it, but tempering it. This delicate manipulation allows the worms to survive while the host avoids the exhausting toll of constant immune activation.
"Helminths are masters of regulating the host immune response," says Briggs, an instructor of medicine in infectious diseases at Yale School of Medicine. "It's not a fluke; most species of helminths have found distinct ways to accomplish this." Her research, detailed in a recent review in Clinical & Translational Immunology, reveals how these parasites dial down the body’s type 2 immune response—the same system that flares during allergies and tissue damage. By promoting what Briggs calls "trained tolerance," helminths teach the immune system to tolerate rather than attack, a shift that could be harnessed to treat autoimmune conditions like Crohn’s disease and type 1 diabetes.
The implications are already reshaping medical research. Briggs is investigating why people with helminth infections show weaker responses to live vaccines, including measles and BCG for tuberculosis, where both the strength and longevity of protection are diminished. At the same time, her lab is exploring how helminth-induced immune modulation could be mimicked in therapies—without the infection. While three helminth species are classified as human carcinogens due to their potential to cause chronic tissue injury, the broader picture is nuanced: in some populations, helminth carriers show lower rates of inflammatory disorders, suggesting a complex balancing act between harm and benefit.
"These are parasites, but they have an interesting story to tell that can help us advance human health," Briggs says. As scientists decode the worm’s evolutionary wisdom, the future may not lie in eradicating all helminths—but in learning from them.