A pinboard by
Marissa Fahlberg

Well, parasites used to be us. And now that they aren't - we are left sneezing for their return.


Our bodies attack parasites and allergens the same way. Scientists want to harness the relationship.

In 10 seconds? The prevalence of allergies is directly related to affluency and industrialization. Scientists believe that the lack of childhood diseases is causing a dramatic hyperactivity of the branch of the immune system that is normally used to fight parasites and other microbes.

It all started with good hygiene… The Hygiene Hypothesis argues that with increased hygiene – daily showers, running water, and toilets – humans encounter fewer microbes than ever, especially in childhood. In support of this idea, epidemiologists have shown that people in rural areas and less developed countries have a much lower incidence of allergies.

How does good hygiene cause allergies? Cells of the immune system that cause allergic reactions are the same as those that attack parasites. According to the hygiene hypothesis, when those cells do not have parasites to attack and are not busy fighting off the microbes that humans used to encounter as children, they can start behaving erratically.

There are additional factors that can influence an allergic response. The incidence of allergies (or not) depends on the timing of parasitic infections (childhood or adulthood), the species of parasite, whether the infection is short-term or long-term, and if the parasite causes the person to become sick.

Wait, I thought parasites always made people sick! Aren’t they bad? Parasites survive off of the nutrition of their host and are thus bad for people on the surface. In children, parasites can be especially painful and cause gastrointestinal discomfort. As people age, however, the immune system can keep the number of worms down and tolerate those remaining, and the worms and person are able to co-exist with minimal symptoms.

What are scientists doing with this information? The general idea is that if scientists can isolate certain parasitic molecules and inject them into people, then hopefully the immune system will be too busy dealing with these particles that they won't cause allergies.

So if I have bad allergies, should I give myself some worms? Probably not yet – there is too much unknown about what wormy concoction will best treat a person’s allergies. However, there is a real possibility that doctors will someday start prescribing parasitic extracts on a specific schedule to get rid of the sneezing and sniffling, and it could very well become a natural and effective solution.


A missing link in the hygiene hypothesis?

Abstract: The incidence of childhood Type I (insulin-dependent) diabetes mellitus has risen in parallel with that of childhood asthma, and the hygiene hypothesis proposes that this is due to reduced stimulation of the immune system by early intercurrent infection. If so, this protective effect is probably mediated by regulatory T lymphocytes. Co-evolutionary partners might have contributed to the development of this form of response, and parasites and the indigenous biota of the gut are plausible candidates. Helminths inhibit the development of atopic disease via induction of regulatory T cells and secretion of Il-10, and pinworms inhibit diabetes development in the non-obese diabetic (NOD) mouse. The most successful human helminth of the western world is the pinworm Enterobius vermicularis, and some 50% of young children in Europe and North America may have been infested around the middle of the twentieth century. Pinworms are benign, usually asymptomatic, and may have immunomodulatory properties that protect against the development of immune-mediated disorders including diabetes and asthma. Their decline in response to improved living conditions might explain a number of features of the epidemiology of childhood atopy and diabetes. The proposed role would be one of immunomodulation rather than disease induction, possibly mediated by interaction with other influences upon the development of the mucosal immune system. This hypothesis could be tested in case-control studies by the development of serological markers or skin testing. If confirmed, identification of the underlying mechanisms could open the way to new forms of immune intervention.

Pub.: 29 May '02, Pinned: 18 Jun '17

Review series on helminths, immune modulation and the hygiene hypothesis: immunity against helminths and immunological phenomena in modern human populations: coevolutionary legacies?

Abstract: Although the molecules and cells involved in triggering immune responses against parasitic worms (helminths) remain enigmatic, research has continued to implicate expansions of T-helper type 2 (Th2) cells and regulatory T-helper (T(reg)) cells as a characteristic response to these organisms. An intimate association has also emerged between Th2 responses and wound-healing functions. As helminth infections in humans are associated with a strong Th2/T(reg) immunoregulatory footprint (often termed a 'modified Th2' response), plausible links have been made to increased susceptibility to microbial pathogens in helminth-infected populations in the tropics and to the breakdowns in immunological control (allergy and autoimmunity) that are increasing in frequency in helminth-free developed countries. Removal of helminths and their anti-inflammatory influence may also have hazards for populations exposed to infectious agents, such as malaria and influenza, whose worst effects are mediated by excessive inflammatory reactions. The patterns seen in the control of helminth immunity are discussed from an evolutionary perspective. Whilst an inability to correctly regulate the immune system in the absence of helminth infection might seem highly counter-adaptive, the very ancient and pervasive relationship between vertebrates and helminths supports a view that immunological control networks have been selected to function within the context of a modified Th2 environment. The absence of immunoregulatory stimuli from helminths may therefore uncover maladaptations that were not previously exposed to selection.

Pub.: 06 Jan '09, Pinned: 18 Jun '17

Helminths and the microbiota: parts of the hygiene hypothesis.

Abstract: In modern societies, diseases that are driven by dysregulated immune responses are increasing at an alarming pace, such as inflammatory bowel diseases and diabetes. There is an urgent need to understand these epidemiological trends, which are likely to be driven by the changing environment of the last few decades. There are complex interactions between human genetic factors and this changing environment that is leading to the increasing prevalence of metabolic and inflammatory diseases. Alterations to human gut bacterial communities (the microbiota) and lowered prevalence of helminth infections are potential environmental factors contributing to immune dysregulation. Helminths have co-evolved with the gut microbiota and their mammalian hosts. This three-way interaction is beginning to be characterized, and the knowledge gained may enable the design of new therapeutic strategies to treat metabolic and inflammatory diseases. However, these complex interactions need to be carefully investigated in the context of host genetic backgrounds to identify optimal treatment strategies. The complex nature of these interactions raises the possibility that only with highly personalized treatment, with knowledge of individual genetic and microbiota communities, will therapeutic interventions be successful for a majority of the individuals suffering from these complex diseases of immune dysregulation.

Pub.: 15 Apr '15, Pinned: 18 Jun '17

Parasites: evolution's neurobiologists.

Abstract: For millions of years, parasites have altered the behaviour of their hosts. Parasites can affect host behaviour by: (1) interfering with the host's normal immune-neural communication, (2) secreting substances that directly alter neuronal activity via non-genomic mechanisms and (3) inducing genomic- and/or proteomic-based changes in the brain of the host. Changes in host behaviour are often restricted to particular behaviours, with many other behaviours remaining unaffected. Neuroscientists can produce this degree of selectivity by targeting specific brain areas. Parasites, however, do not selectively attack discrete brain areas. Parasites typically induce a variety of effects in several parts of the brain. Parasitic manipulation of host behaviour evolved within the context of the manipulation of other host physiological systems (especially the immune system) that was required for a parasite's survival. This starting point, coupled with the fortuitous nature of evolutionary innovation and evolutionary pressures to minimize the costs of parasitic manipulation, likely contributed to the complex and indirect nature of the mechanisms involved in host behavioural control. Because parasites and neuroscientists use different tactics to control behaviour, studying the methods used by parasites can provide novel insights into how nervous systems generate and regulate behaviour. Studying how parasites influence host behaviour will also help us integrate genomic, proteomic and neurophysiological perspectives on behaviour.

Pub.: 12 Dec '12, Pinned: 18 Jun '17

Helminths and the IBD hygiene hypothesis.

Abstract: Helminths are parasitic animals that have evolved over 100,000,000 years to live in the intestinal track or other locations of their hosts. Colonization of humans with these organisms was nearly universal until the early 20th century. More than 1,000,000,000 people in less developed countries carry helminths even today. Helminths must quell their host's immune system to successfully colonize. It is likely that helminths sense hostile changes in the local host environment and take action to control such responses. Inflammatory bowel disease (IBD) probably results from an inappropriately vigorous immune response to contents of the intestinal lumen. Environmental factors strongly affect the risk for IBD. People living in less developed countries are protected from IBD. The "IBD hygiene hypothesis" states that raising children in extremely hygienic environments negatively affects immune development, which predisposes them to immunological diseases like IBD later in life. Modern day absence of exposure to intestinal helminths appears to be an important environmental factor contributing to development of these illnesses. Helminths interact with both host innate and adoptive immunity to stimulate immune regulatory circuitry and to dampen effector pathways that drive aberrant inflammation. The first prototype worm therapies directed against immunological diseases are now under study in the United States and various countries around the world. Additional studies are in the advanced planning stage.

Pub.: 06 Aug '08, Pinned: 18 Jun '17