Hookworm…in pregnancy?

hookworm in pregnancy

Every six years or so, social media explodes with hysteria about parasites. As the lifelong rebel and devil’s advocate I am, I’ve delved quite a bit into research on the potentially beneficial role of parasites…more on that later. 

But what about parasites (specifically hookworm) in pregnancy?

I recently read this article to gain an understanding of the implications of a common parasitic infection during pregnancy—hookworm.

You may be surprised to know that hookworm infection affects about 25% of pregnant people worldwide and that pregnancy is a state that favors increased chances of hookworm infection. Hookworm infection is a cause of anemia. Because the demand for nutrients during pregnancy can cause anemia, hookworm in pregnancy may be an underappreciated factor in many cases of anemia during pregnancy.

Why does the risk of hookworm infection increase during pregnancy? 

“[D]ue to immunological characteristics shared by hookworm and fetus, changes in maternal immunity aimed at ensuring immune tolerance of a fetus may dampen the immune response to hookworm during pregnancy. As a result, pregnant women may experience both higher susceptibility to new hookworm infections and higher morbidity due to existing infections, manifesting as greater hookworm-driven blood loss.”

This may all sound really bad, right? 

However, hookworms, along with other helminths, are often referred to as “old friends” because of certain immunological advantages that they confer to their human hosts. 

In fact, as the study authors note, “tradeoffs between helminth exposure and allergic responses … highlight an apparently evolved dependency on these parasites for calibrating immune function.” 

These immune changes may lower susceptibility to certain illnesses, including Giardia lamblia, malaria infection, some autoimmune conditions, and allergies.

Experimental helminth infection has been studied as a therapeutic approach to managing allergic and autoimmune diseases and even metabolic disorders like type 2 diabetes. In these helminth studies, participants are willingly infected with a parasite in a controlled setting and monitored to ensure that the parasite survives and the infection is viable. 

This may sound like your personal nightmare, and given the recent popularity of parasite detoxes, it may also sound completely bonkers. 

Why would anyone want to be intentionally infected with a parasite like hookworm?

The answer lies in the Old Friends Hypothesis—the idea that humans co-evolved with various diverse organisms, the “old friends” mentioned above, that play a vital role in training and regulating the immune system. The human relationship with these organisms is particularly important to the developing immune system during early infancy and childhood. These old friends include human gut microbes, parasites, and beneficial organisms from the natural environment. 

However, as our societies have modernized, we have collectively lost contact with many of the microbes needed for optimal immune resiliency. 

Contact with the immunoregulatory ‘Old Friends’ rapidly diminishes when industrialization occurs, and individuals start to inhabit a plastic and concrete environment, to consume washed food and chlorine-treated water, and to minimize their contact with mud, animals and faeces. This withdrawal of the organisms that drive immunoregulatory circuits results in defective immunoregulation that, depending on the genetic background of any given individual, can manifest as a variety of chronic inflammatory disorders, including allergies, IBD and autoimmunity. 

So, the idea behind helminth therapy is that because we evolved with parasites, intentional infection may have immunomodulatory effects that benefit certain people. 

Parasitic infection drives a Th2 (T helper type 2) immune reaction in the host, increases T-regulatory cells and decreases inflammatory cytokines. Fascinating research has also shown that parasite infection can improve gut barrier integrity and increase gut microbial diversity, resulting in lower levels of gut inflammation

But what about the side effects of parasitic infection? I’m sure everyone has heard some version of a horror story involving symptoms like severe weight loss, nutrient deficiencies, diarrhea, bloating, and general malaise.

Helminth infection can indeed cause symptoms like these, but common parasites such as hookworm may go mostly unnoticed in many cases. 

 A 2011 double-blind placebo study examined helminth therapy in adults with Celiac disease to see if hookworm infection would suppress the immune reaction to gluten

Participants in the helminth group reported intestinal pain during the initial infection and also reported increased nausea, bloating, and flatulence. However, their well-being did not suffer, and they had reduced feelings of lethargy compared to the control group. 

Interestingly, despite these initial symptoms, all participants declined deworming treatment by the end of the study. 

The choice to retain hookworm infection has been observed in other studies as well, like this 2023 clinical trial studying the effects of hookworm therapy on insulin resistance in adults at risk of T2DM

In this study, after being inoculated with hookworm, 44% of participants reported mild to moderate GI symptoms such as bloating, vomiting, nausea, feeling hungry, abdominal pain, stomach cramps, and changes in motility. However, the majority of these adverse effects were resolved without intervention. Three participants were removed from the study due to severe symptoms and provided with deworming medication to resolve their symptoms. 

Along with uncovering the interesting observation that many of us seem to be remarkably tolerant of hookworm infection, these studies provided some fascinating findings on the therapeutic benefits of helminth therapy. 

For adults at risk of T2DM, hookworm infection may significantly improve insulin sensitivity. This was demonstrated in the 2023 study above, where HOMA-IR was reduced from 3.0 at baseline to 1.6 eighteen months after hookworm infection. This is quite significant as a HOMA-IR of 3.0 indicates severe insulin resistance that precedes the onset of type 2 diabetes, while 1.6 is within a healthier range

For the CD study, results were insightful yet less promising, with the authors concluding that,

 “We observed at best weak trends towards reduced numbers of gluten peptide-specific T cells in blood and histological damage following wheat challenge in CD.”

Now that I have given you an idea of why hookworm infection isn’t always a bad thing let’s get back to the article we began with.

A closer look at hookworm in pregnancy. 

Hookworm infection in pregnancy conveys both advantages and disadvantages. As the authors state, it “might be detrimental, exacerbating anemia and susceptibility to comorbid infections” and “might also be positive, facilitating maternal tolerance of the fetus and decreasing risk for preeclampsia and miscarriage.” 

During the period of lactational amenorrhea, the postpartum period where the mother is breastfeeding her baby but has not yet resumed menstruating, hookworm infection has no adverse impact on hemoglobin levels.

Fascinatingly, “From an immunological viewpoint, a human fetus shares a number of broad similarities with hookworm and other helminths. Both are fairly long-term inhabitants of the maternal body, are genetically distinct from the host/mother, and rely on the resources of the maternal body for sustenance. In light of this, it is plausible that helminths may have evolved to utilize strategies similar to the human fetus to avoid the maternal body’s immune response.”

The study showed that in pregnancy, hookworm caused a slight drop in hemoglobin and raised erythrocyte sedimentation rate (ESR), a marker of inflammation. 

These markers had the most impact during the first trimester and less during the second and third. The average ESR of first-trimester women with hookworm was 39% higher than first-trimester women without hookworm. In comparison, non-pregnant women with hookworm had an average ESR of only 10% higher than their hookworm-free counterparts. 

Unlike their non-pregnant counterparts, pregnant people with hookworm infection do not produce significantly higher eosinophils than people without hookworm infection, so this may be one mechanism for increased susceptibility to hookworm infection during pregnancy. Why don’t eosinophils increase in pregnant people infected with hookworm? Higher eosinophils are a risk factor for pregnancy loss, and the body appears to prioritize maintaining the pregnancy over fighting hookworm.

Want to learn more?

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