Periodontitis and a little protozoan parasite: Entamoeba gingivalis

by AR

Figure 1: Schematic of periodontitis

What is Periodontitis? Well, periodontitis is a serious gum infection that destroys the gums and underlying bone that support maxillary and mandibular teeth (1). This disease causes major inflammation of the gingiva, as seen in Figure 1. The gums pulled away from the teeth are characteristic of periodontitis, compared to its earlier gingivitis stage with the gums in contact with respective teeth. Ok, periodontitis can’t be that big of a problem, right? Wrong! The American Academy of Periodontology warns of a significant public health problem: 50% of American adults suffer from gum disease—that’s 64.7 million adults age 30 years and older! If not treated properly, periodontitis develops into a severe stage.

Figure 2: Severe periodontitis

This is one of the most prevalent oral diseases—5% to 20% of the population is affected with severe periodontitis, and is one of the biggest threats to dental health. Bacteria in the oral cavity infect the tissue that surrounds the tooth (or teeth) and this progresses to periodontal disease. Bacteria colonize and form plaque, when this plaque hardens it is termed tartar. The build-up of tartar is capable of spreading below the gum line and causing recession of the gums, as seen in Figure 2. Entamoeba gingivalis was first found in plaque between teeth with severely diseased periodontitis patients using light microscopy. This protozoan parasite has been affiliated with periodontitis for over one hundred years, but its role in this oral disease is not yet entirely understood (3). Periodontitis is not entirely understood either; the classification of periodontal diseases were revised three times within the last eleven years (4). This leaves much to be learned about periodontitis and the specific role E. gingivalis plays in the oral disease.

So periodontitis causes a potentially severe oral disease that results in detrimental effects in oral health in humans or any other host. But has anyone thought about periodontitis from this little protozoan parasite’s point of view? …

Well, I am just a little one-celled protozoan parasite trying to do what I can and survive.

Figure 3: Entamoeba gingivalis

*The dark circle is my lunch-
an engulfed erythrocyte     

The gingiva in the oral cavity is my home. I love to bury deep in the diseased gingival pockets, but healthy gingival sites near the base of the teeth will work too (5). The characteristic periodontal recession of gums allows me easier access to the gingival pockets to make myself at home. Periodontitis is largely due to the accumulation of bacteria, which is why I thrive when people have severe periodontitis—more food for me! My home is made more luxurious when there is significant bone loss in my host and when teeth become mobile—this allows me to colonize easier and greatly increases my access to available food. My pseudopod surrounds and captures my meals and then I enclose it in a food vacuole. Although, most often the numerous bacteria in the oral cavity serve as my meals, I like to switch it up and sometimes feed on nuclear fragments of leukocytes and *erythrocytes (see Figure 3). I am the only species of amoeba that has the privilege of eating human host red blood cells and white blood cells (to give you a comparison, a leukocyte is about ten times smaller than I am, Ha). The vast difference in size plays a major role in my ability to engulf a leukocyte via phagocytosis. I really am not a mean predator; I just like switching my meals. C’mon, who likes eating the same thing every day? Nobody.

Well, enough about food..moving on.. so….How many people have you kissed on the lips lately? Hopefully a lot. My transmission from host organism to host organism is direct. This includes transmission via kissing, sharing food utensils, or sharing beverages. I exist in a trophozoite stage that enables me to invade and colonize another host. Humans know that my trophozoite stage of life is a noninvasive colonization of my type of amoeba (2).  In contrast to my close relatives, I have no known cyst stage (2). Humans still have much to discover about my life cycle. Learning more about my life cycle will most likely help humans to clinically identify me.

It may be hard to clinically identify me because I’m sneaky —and sometimes resemble a human host macrophage (4). As far as humans can tell, modern immunological or biological techniques may not always detect my presence in an oral cavity. Works for me! Consequently, the relentless human mind discovered that morphological techniques must be used to identify me (4). My presence is used in conjunction with certain bacterial species to diagnose periodontal disease.

It should be noted, I do not intend to cause harm to my hosts—I am just trying to survive and thrive as a tiny protozoan parasite. The warm, moist environment in an oral cavity is great for bacterial growth. And since I feed on primarily bacteria, this is a great place to call home. Even more, the characteristic accumulation of bacteria present in periodontal disease is my paradise. My role in periodontal disease is quite controversial lately, since I have been found not only in diseased gingiva but also healthy tissues of human hosts. There is much to be learned about my existence and prevalence in oral cavities both in hosts with and without periodontal disease.

References:

1. N.d. n.p. Web. < 1.http://www.mayoclinic.com/health/periodontitis/DS00369 >. (Figure 1)
2. www.jstor.org.ezp2.lib.umn.edu/stable/10.2307/3224205
3. http://www.springerlink.com.ezp2.lib.umn.edu/content/n353183q60g0n155/fulltext.pdf
4. http://www.nrcresearchpress.com.ezp1.lib.umn.edu/doi/pdf/10.1139/m96-161
5. Rohrer, Finlo. Pros and cons of DIY dentistry. 2007. BBC News MagazineWeb. <http://news.bbc.co.uk/2/hi/uk_news/magazine/7045263.stm>. (Figure 2)
6. Upton, S.J. Entamoeba gingivals. N.d. K-StateWeb. <http://www.k-state.edu/parasitology/625tutorials/Egingivalis.html>. (Figure 3)