Healthy horrors: the benefits of parasites
Submitted by brown on 23 August 2011
However, instead of sitting inside the guts of dogs, cats or humans, these worms spend their days residing in the guts of sharks, robbing the predators of nutrients by absorbing them before the sharks can. Whereas small numbers of tapeworms simply force the animals they infest to feed more often, large populations can make host animals very ill.
Yet, a research study conducted by Masoumeh Malek at the University of Tehran in Iran and a team of colleagues found that these parasitic worms might provide a critically valuable service to their hosts.
So these worms, while stealing some nutrients from the sharks’ guts, are likely providing an invaluable service to the sharks by functioning as filters that protect the predators from becoming poisoned by heavy metals (Malek et al., 2007).
Findings like those in this study are throwing the definition of a parasite into confusion. Parasites are supposed to take what they need, harm their host in the process, and give nothing in return. In contrast, organisms called mutualists provide a benefit to their host and receive some benefit in return; organisms called commensals provide a benefit to a host but do not get anything in return. What role the shark worms, which are traditionally considered to be parasites, are playing is difficult to determine. And such confusion is not unique to shark parasites; many parasites that have a penchant for using humans as hosts are also raising questions.
The logic behind Turton’s actions relied on the idea that allergies, eczema and asthma are overreactions of the immune system. Under normal circumstances, the immune system searches for harmful organisms and destroys them. However, in patients suffering from allergy, eczema and asthma, the immune system attacks not only harmful organisms, but also materials that are not actually a threat.
Although Turton’s work certainly made a point, his experiment only involved a single participant, himself. Good science however requires studies with many participants, and repeated experiments to confirm results. David Pritchard and his colleagues at the Nottingham University School of Pharmacyw1, UK, are seeking to do exactly this.
For years, Pritchard’s team has been looking at allergy and asthma prevalence in both developing countries, where parasitic worms are common, and developed countries, where they are almost entirely absent. They have confirmed the results of many colleagues, who find that allergies are often absent in regions where parasitic worms are commonly found inside people. This may suggest that parasites protect people from allergies and asthma, but because so many other conditions differ between developed and undeveloped countries, which may also play a role, it is impossible to be sure.
Of course, even if the research proves that parasites can help treat allergic conditions, the question remains whether many people would be willing to follow in Turton’s footsteps, swallowing a mouthful of worm larvae as a medicine. Luckily, they may not have to: at Strathclyde University in Glasgow, UK, a team of researchers led by William Harnett is experimenting on a complex protein that is created by a parasitic worm (Acanthocheilonema viteae) which infects rodents. Their research suggests that even in the absence of the worm, the isolated protein has the ability to reduce allergic inflammationw2.
Although much work is needed to fully understand what this protein is actually doing, there is a real potential in trying to use parasite proteins to control conditions such as allergies, asthma and eczema. Perhaps the public would find this solution a little more palatable?
Garner S, Thomas R (2010) Evaluating a medical treatment. Science in School 16: 54-59. www.scienceinschool.org/2010/issue16/clinical
Malek M et al. (2007) Parasites as heavy metal bioindicators in the shark Carcharhinus dussumieri from the Persian Gulf. Parasitology 134(7): 1053-1056. doi: 10.1017/S0031182007002508
Turton JA (1976) IgE, parasites, and allergy. The Lancet. 308(7987): 686. doi: 10.1016/S0140-6736(76)92492-2
w1 – To find out more about the work of David Pritchard and his colleagues, see: www.nottingham.ac.uk/pharmacy/people/david.pritchard
w2 – For more information about William Harnett’s work, see: http://spider.science.strath.ac.uk/sipbs/staff/Billy_Harnett.htm
w3 – To find out more about the author, Matt Kaplan, see: www.scholarscribe.com
To learn about further research into worm parasites, see:
If you enjoyed this article, you might like to browse other science topics in Science in School. See: www.scienceinschool.org/sciencetopics
Matt Kaplan is a professional science journalist, based in both London, UK, and Los Angeles, CA, USA, who regularly reports on everything from palaeontology and parasites to virology and viticulture. When not stuck behind a desk, he runs wilderness expeditions in far-flung regions of the world. See his websitew3.
This article is an excellent introduction to the different types of interactions between organisms and could be used in many ways.
Several types of parasite are discussed in the article. Where do we meet parasites in everyday life? Students might, for example, thinks of endoparasites like worms in cats, dogs and aquarium fish or of ectoparasites such as ticks, lice and leeches. In which organ systems do these parasites occur and what effects do they have on their hosts? Perhaps the students could investigate the dangers and uses of leeches throughout history. They could also investigate the life cycle of a particular parasite and think about how its anatomy is adapted to its way of life.
The article goes on to investigate the interaction of parasites with the immune system and could be used to introduce a discussion about the immune system, its constituents and regulation. What about when the immune system itself causes problems? How much do the students know about asthma and allergies? Do any of them suffer from allergies? What are the causes, how can these allergies be treated in the long run and how should the students react in an emergency?
The author then introduces the idea of using parasites or parasite extracts to treat allergy conditions. How much do the students know about conventional medicine? Perhaps they could discuss antibiotics and bacterial resistance, and whether they think parasites could, in future, be used as an alternative or supplementary medicine? They could also discuss how new treatments are developed and tested (see Garner & Thomas, 2010).
Should treatments be tested only on volunteers, or is it the duty of all citizens to undergo such testing? Who should pay for the research and who profits from it? Is it right for medicines to be patented? What about patenting things like gene sequences or genetically modified organisms?
Morten Schunck, Denmark