Parasites Revisited
BY ALPER ÖZKAN (MSN/PhD I)
Note: Read at your own peril. This is your only warning.
I dislike noise and crowds, and our spring festival invariably creates unbearable amounts of both. Much to my surprise, though, I very much liked this year's iteration! I have a sweet tooth, so I enjoyed all those stands vending various sweets. A flimsy stage was hastily crafted over the ever-familiar small pond in the midst of the campus, so I enjoyed watching the performances just to see if anyone would fall through it (fortunately for the performers, no one did). And right next to the death pond was what I took to be an attempt to cross wish trees with an off-season Tanabata, which I found to be interesting to say the least.
But the festival is over, and now I must close this semester with a final column before slaving away to develop my current research topic during the summer, so here I am, pondering about what to write. (No, I don't get a summer vacation. Enjoy your days as undergraduates, because you'll be missing them once you join me among the ranks of graduate students.) Well, since in the previous column I didn't discuss parasites that cause more severe effects, now is a good time to do so! I'm already past the deadline, but I have a fairly decent grasp of parasites, so I'll be able to write this at a reasonable speed instead of scrambling around on Wikipedia for details. I won't go all out, but do know that this week is for the true movers and shakers!
Do you like sushi? Rest assured that you won't anymore. Many parasites spend their lives partially or entirely in either water or water-dwelling animals, so it's no surprise that many of them make use of fish as intermediate or final hosts. Anisakis is one such worm that relies on fish to reach its final host -- fish-eating marine mammals in this case. But occasionally something goes not quite as planned, and the poor larval worm's transfer vehicle is eaten by a human instead of a seal or dolphin, and the parasite, unequipped to handle the situation, causes a few complications. By a few complications, I mean that fish goes in; worms come back out, sometimes alive and kicking. (Well, figuratively at least. They're worms, so they have a few problems in the kicking department.) This is the best-case scenario, as it's even worse if Anisakis passes through the digestive tract -- the larvae can cause more severe effects in this case, possibly because they also possess potent allergens. What makes Anisakis particularly annoying is that it retreats further into the fish when exposed to cold, so freezing the fish does not kill the worms very easily, making them ideal agents for infiltrating any sort of raw fish dish. So, while very rare in humans (with only about 1,000 cases per year even in Japan, where raw fish is regularly consumed), Anisakis is still something to consider before ordering fish sushi. But feel free to enjoy other types of sushi, at least until I find enough time to write about the parasites lurking in those.
Do you like hot springs? Rest assured that you won't anymore, as the next parasite to be covered is the infamous brain amoeba Naegleria. To give the protozoan due credit, it isn't always a parasite -- in fact, it's entirely content to munch on bacteria and bears no particular grudge against humans. It is fond of rather high temperatures and is often found inhabiting hot springs as well as other warm water sources, such as ponds, where it encounters swimmers and sometimes decides to earn its name as the brain amoeba. Normally, the brain is extremely well-protected, since the blood vessels surrounding it are tightly bound, allowing only select chemicals (and certainly no giant amoebae) to pass through. Diseases that affect the brain therefore have to get creative to reach their target -- the rabies virus, for example, enters peripheral nerves first and then infects its way into the brain. Naegleria instead uses one of the few unprotected areas where the blood-brain barrier can be bypassed, namely the cribriform plate, a bone structure located in the roof of the nose. This plate connects to the olfactory bulb and has holes large enough for Naeglaria to crawl through, so any lucky brain amoeba that ends up in the nose can easily reach a large feast in the form of unprotected brain tissue. This tissue is consumed by a sucker formed by the amoeba, which eats its way into the brain and causes death in about two weeks, with a fatality rate over 98 percent. In comparison, glioblastomas are among the deadliest cancers and even they give you a grace period of about a year.
If you're still not worried, you may want to know that even common molds can sometimes cause infections in man, attacking the nose first (because mother nature hates you, of course) and sometimes causing such damage as to necessitate the surgical removal of, well, the entire nose. And the eyes.
...And sometimes, parts of the brain. Mucormycosis is terrifying.