Friday March 27 2026
JORDAN INGLIS FOR VARSITY
The global disease burden has shifted. Less than a century ago, healthcare systems and human lives were burdened by infectious diseases caused by bacteria, viruses, and parasites. With the development of highly effective vaccines and antibiotics, humanity has gone from being largely at the mercy of microorganisms to controlling many of them. Of course, infectious diseases still pose a significant risk to human health – especially in areas where access to medical care remains limited. But while infectious disease persists largely because of political and economic barriers, rather than scientific ones, a new category of illness has emerged, one that modern medicine is still struggling to understand: Immune-Mediated Inflammatory Disease.
Immune-Mediated Inflammatory Diseases (IMIDs) include asthma, allergies, rheumatoid arthritis, inflammatory bowel disease (IBD), psoriasis, and more. Although these conditions appear clinically distinct, they share a common feature: an overactive immune response to otherwise innocuous stimuli such as peanuts, dust mites, or even the body’s own tissues. This immune reaction triggers inflammation, which can occur suddenly – as in an asthma attack – or persist long-term, as in many autoimmune conditions.
Complex inflammatory diseases can be likened to an ecosystem under stress. Disruption by spraying pesticides – or, in medicine, administering immunosuppressants – may temporarily address an immediate problem, but they do not restore balance to a dysregulated system. Pharmaceuticals are by no means detrimental: pharmacological treatments have dramatically improved outcomes for patients with IMIDs. For example, countless deaths from anaphylactic allergy have been prevented by adrenaline injections via EpiPens, and increasingly refined therapies help manage pain in autoimmune conditions. Yet IMIDs continue to rise in prevalence and remain largely incurable. Ultimately, the goal of treatment would be to restore immune homeostasis – and that’s where parasites come in.
“Helminths secrete factors that interact with the host’s immune system, softening or redirecting immune responses to avoid damage to the parasite”
Helminths, commonly known as parasitic worms, are a diverse group of worm-like invertebrates that survive inside – and feed from – living animal hosts. They often inhabit the intestinal tract, where they can persist for years and may cause disease by impairing nutrient absorption. However, the severity of disease depends on the ‘worm burden’ – the number of parasites infecting the host. A low worm burden is typically asymptomatic, while higher burdens can lead to malnutrition, weakness, and impaired growth, with particularly severe consequences for children and immunocompromised individuals.
But in cases where infection is asymptomatic, an intriguing question arises: how can a large, multicellular organism live inside the human body for years, without the immune system launching an attack? Isn’t detecting and eliminating invaders precisely what the immune system evolved to do?
The answer lies in immunomodulation. Helminths secrete factors that interact with the host’s immune system, softening or redirecting immune responses to avoid damage to the parasite. These secretions inhibit the proliferation of the CD4+ T-helper immune cells that would normally target extracellular parasites, while promoting regulatory T cells that curb the inflammatory response. Helminth-derived molecules also interfere with the production of cytokines – the chemical messengers of the immune system.
In effect, helminths shift the immune system from a Th2 to a Th1 mediated response – essentially, encouraging immune cells to focus on intracellular bacteria and viruses to distract from the parasite. Crucially, the parasite does not ‘want’ the host to die, or even to become severely ill. Although helminths and hosts compete for nutrients, the parasite ultimately depends on the host’s survival in order to reproduce and transmit its eggs.
“Although helminths and hosts compete for nutrients, the parasite ultimately depends on the host’s survival”
For much of human history, helminth infection was a near-universal experience. Once scientists identified large worm burdens as a cause of disease, widespread efforts to eradicate them followed. The problem and its solution seemed straightforward: worm infections cause disease, and so eliminating them should improve health.
Improvements in sanitation reduced parasite transmission through contaminated food and water, while deworming drugs allowed rapid and effective parasite clearance. Global deworming campaigns continue today in low-resource settings to reduce the significant morbidity caused by helminth infections. Yet an interesting pattern has emerged: helminth eradication is closely intertwined with a surge in prevalence of IMIDs.
From an evolutionary perspective, the human immune system is still not used to life without parasites. Humans evolved in synergy with these worms, to an extent dependent on suppression by their secreted factors to keep inflammation in check. Helminths may also play a role in immune ‘training’, helping prevent immune cells from attacking the body’s own tissues or harmless environmental stimuli.
“From an evolutionary perspective, the human immune system is still not used to life without parasites”
Research also suggests that helminths interact with organisms in the gut microbiome in ways that reduce inflammation. Mounting evidence indicates that healthy immune function depends not on a single organism, but on a complex biological ecosystem.
In this sense, our relationship with helminths mirrors that with bacteria. When microbes were first discovered, they were largely viewed as enemies of human health. Only later did scientists recognise that many bacteria are essential to normal physiological function. Today, the microbiome is understood to play a critical role in digestion, immunity, and disease prevention.
A human completely devoid of microbes on their skin or in their gut would struggle to maintain normal physiological function – and would actually become more vulnerable to infection because empty ecological niches allow harmful microbes to colonise As a result, modern discussions of health increasingly emphasise maintaining a diverse microbiome through diet, probiotics, and careful antibiotic use. Perhaps it is time to reconsider helminths in a similar light.
Current medical research suggests that helminth-based therapies for IMIDs may be on the horizon. Inoculation with helminths such as Necator americanus or Trichuris suis has been shown to alleviate symptoms in patients with inflammatory bowel disease. Helminths can also influence intestinal cell secretions to promote beneficial gut bacteria that support an anti-inflammatory state.
In asthma, infection with species such as Schistosoma mansoni, Heligmosomoides polyrus, and Trichinella has shown promise to reduce allergic inflammation, but with variable efficacy. Live inoculation with parasites to treat inflammatory disease is fickle – parasites are complex multicellular organisms whose biology scientists are still decoding.
“Medicine is faced with the challenge of balancing the burden of infections with that of immune-mediated inflammatory disease”
A safer alternative may be to isolate the molecules helminths use to regulate the immune system and develop them into targeted therapies. Yet studying helminths in the laboratory is challenging, as many species require living hosts to survive. Moreover, reducing the complex ecological interactions between parasites, microbes, and the immune system to a handful of isolated molecules may oversimplify a much more intricate biological system. For this reason, helminths may ultimately prove more useful in preventing, rather than treating, inflammatory diseases.
The consequences of reduced helminth exposure raise an important question: can these organisms truly be classified only as pathogens? High parasite burdens undeniably cause serious disease, particularly affecting childhood development and potentially leading to lifelong disability. But the complete helminth eradication is clearly not a perfect solution either, as it could contribute to immune dysregulation and the rising prevalence of autoimmune diseases and allergies. And, in light of this information, medicine is faced with the challenge of balancing the burden of infections with that of Immune-Mediated Inflammatory Diseases.
So while deliberately infecting yourself with worms is certainly not advisable, it is possible that one day a low helminth load will be normalised and we take inspiration from our ancient companions in treating disease.
