Based on my knowledge of parasite biology and according to the context of Genesis (all the creatures are created for a good or a purpose)1, I believe that the purpose of creating parasites is to control the balance of life. The parasites are needed to cause infection or disease to stop the outgrowth or spread of a species in specific conditions. Some examples of these conditions are, when there are no predators for that speciates, the number of predators is less than the number of prey, or when the apex predators who stand at the top of food chain dont have any predator. In other words, the parasites are crucial for keeping the species growth stabilized and to maintain balance. Thus, the parasites are needed to cause infection to some species that will ultimately result in their death and therefore the number of deaths will balance with the number of births. As a result of parasite existence, the nature is able to keep the balance of all the living species properly in our planet.
Parasites play a major role in diversification in life and also play a major role in limiting speciation (in their hosts or prey). Parasites also force sympatric diversification if there is a spread of exploiter-resistance strategies or health fees related to exploiter resistance. Parasites can also pressure allopatric diversification by creating exclusive choice pressures and increasing the rate of random divergence.
According to the article Parasitic worms and inflammatory diseases when sanitation and access to clean food and water became a common life standard for most individuals and the use of antibiotics became common after World War Two, this have caused a dramatic alternation to the exposure to bacterial pathogens and led to the emergence of autoimmune inflammatory diseases. This suggests that early infections with parasites decreases the risk of autoimmune diseases because the parasites keep the immune system occupied.2 In conclusion, it is safe to say that parasites and microbes have been important for shaping and tuning the evolution of the human immune system.
It is important to also mention when speaking of parasites that even though normal microflora in our bodies are opportunists, they prevent colonization by more harmful microbes, which can cause many fatal infections.
One example of a parasite is leeches ,which are segmented predatory worms that belong to the phylum Annelida and comprise the subclass Hirudinea, they are found taking blood meals from animals. However, leeches can help in removing blood clots from the body and are successfully used in this leech therapy.3
1. Genesis. Word Books, 1987.
2. Zaccone, P et al. Parasitic worms and inflammatory diseases. Parasite immunology vol. 28,10 (2006): 515-23. doi:10.1111/j.1365-3024.2006.00879.x
3. Abdualkader, A M et al. Leech therapeutic applications. Indian journal of pharmaceutical sciences vol. 75,2 (2013): 127-37.
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Excellent work on this weeks discussion post! I liked how you gave a well-rounded argument for the inherent potential goodness of the origin of parasites. For instance, I found it fascinating that you mentioned how autoimmune diseases became more prevalent after the riddance of parasites and other pathogens from our water sources, thereby suggesting that parasites have a role in keeping our immune systems in perpetual balance. I noticed you chose leeches as your parasite of discussion and provided their assumed original role to have been therapeutic in nature, most likely involving the extraction of blood clots. This seems to make intuitive sense, as all things were originally created very good (Romans 8:22).
In my scientific research I also came across material that would suggest leeches be beneficial for all.1 According to Dr. Otts team from West Virginia, medical leeches (Hirudo verbena) contain within the mucus they shed a whole other group of symbionts that can be obtained via horizontal gene transfer.1,2 These can include species such as the Aeromonas veronii, the proteobacterium, as well as those of the Pedobacter genuswhich contain heparinase (breakdown of heparin for anticoagulation).1 Additionally, Rikenella-like is another mutualist found in the gut of leeches, alongside that of the A. veronii.1 Therefore, not only is the leech a mutualist itself, as you pointed out, but there even seems to be evidence for additional symbionts contained within the symbiont!1,2
In my biblical research, I found this passage from Proverbs 30:15 which reads; The leech has two daughters: More and More. There are three things that are never satisfied, four that never say, enough. Although highly interpretational, I feel this passage gives us some insight to parasitism from a biblical view. Although the allusion to the leech is referencing human greed as a general theme, so it is with parasitology, albeit by necessity for the latter. This is clear not only because the leechs childrens names are More and More, but because additional offspring keep showing up before the passage even finishes. This does not provide us with any glimpse into what original purpose was meant to be for the leech, but merely a reminder that at the time this was written, (supposedly 700 B.C.), that parasitism was already prevalent on the mind, and used to conjure morals.
Again, great work this week! Good luck on the final exam!
Ott, B. M., Rickards, A., Gehrke, L., & Rio, R. V. (2015). Characterization of shed medicinal leech mucus reveals a diverse microbiota. Frontiers in microbiology, 5, 757.
Graf, J., Kikuchi, Y., & Rio, R. V. (2006). Leeches and their microbiota: naturally simple symbiosis models. Trends in microbiology, 14(8), 365-371.
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