Thursday, December 5, 2013

Just when you thought it was safe to go back in the water…


             The Great White Shark is one of the most notorious aquatic predators in the public’s eye thanks in part to author Peter Benchley and his 1974 novel Jaws. A whole new world of fear was shown to the world through the pages of Benchley’s book and the frames of the following film adaptation. These works of fiction demonstrated that ocean is dangerous place, and many people now believe that the sharks are some of the most dangerous creatures on Earth. Unfortunately, these people are wrong. The true terrors of the planet wait silently out of sight, all around the world. Microscopic murderers can lurk in water, on land, and in the air. These tiny creatures can and want to eat you, but unlike sharks they cannot do it alone. Microorganisms can exponentially reproduce in a matter of minutes and completely overwhelm every defense your body throws up. There are hundreds of species of sharks worldwide, but this number isn’t even close to the number of different species of microbes in a glass of water! Waterborne, or mostly waterborne, infectious microbes are especially dangerous due to the ease at which they can move from one place to another. Much like the titular shark in Jaws they can strike without warning and in the most unexpected ways.
Cryptosporidium parvum as seen under a microscope
             Cryptosporidium parvum, an apicomplexan pathogen, causes the human disease Cryptosporidiosis, which is an infection of the gastrointestinal tract. Cryptosporidiosis arises following the accidental ingestion of specific C. parvum cells, called thick walled oocysts, through contaminated water, food, or other objects. These determined cells then infect the stomach, both the small and large intestines, and everywhere in between (1). The infection of humans is only one particular stage in this protozoan’s life cycle (Figure 1). During the rest of its cycle, C. parvum simply multiplies, often in the water, waiting for its next chance to strike. In Jaws, the massive shark was said to only do three things: eat, swim, and make more sharks, and this is exactly with Cryptosporidium does. While Jaws simply wants to eat people outright, C. parvum would rather use people to make little apicomplexans to fulfill its life cycle. In the films, the shark would often target certain people over others, like Chrissie Watkins in the opening scene or the young Alex Kitner on his raft, and C. parvum does this as well. People with a compromised immune system (HIV+ people for example) are especially at risk from this debilitating microbe and need to be extra careful when at a high risk of exposure, for example while swimming in a lake (2). These people need to pay special attention to “beach closed” signs around Cryptosporidium’s hunting grounds. Although spending a great amount of time in water, C. parvum also can live on the land, making this microbe not strictly speaking waterborne. Like the massive shark in Jaws, microbes can strike from almost any angle or any place, whether it is in the water by the lake, or on the back of the Orca out at sea.
General lifecycle of Cryptosporidium parvum in humans
             As is the Hollywood way, when something makes money you make a sequel. Unfortunately, this meant that Spielberg’s masterpiece spawned 3 separate sequels in which a random, giant shark just kept coming back to attack the beaches of Amity Island. In every film, it was harder and harder to actually kill the shark because the beast’s tactics and behavior would change in the new and different environments provided in the sequels. This applies to Cryptosporidiosis in that C. parvum cells are clever enough to use their surroundings to evade a quick death. One of C. parvum’s favorite places to turn to in a pinch is biofilms. Biofilms are essentially massive groups of different microbes contained in a matrix of liquid comprised of the many organisms’ secretions (3). C. parvum can hide in biofilms because of the protection they offer, in the same way that the shark hid under Quint’s boat, the Orca, in the original Jaws. Under the Orca, the protagonists couldn’t even see the shark, let alone attack it; and C. parvum uses the exact same method to protect itself from harmful radiation. One study showed that biofilms actually shield the Cryptosporidium from harmful sunlight (4), essentially acting as a form of suntan lotion. A separate study showed that C. parvum could go into biofilms simply to sustain themselves within the biofilms and even help the biofilms build itself faster (5). Biofilms in general are like small, protected, ecosystems that can spread like a disease. As these communities of cells spread widely, so would Cryptosporidium. The shark in Jaws used the deep ocean the same way that this organism uses biofilms to hide, reproduce, and be safe from predators and chemicals alike.
             In Benchley’s book, the shark eventually died from all the wounds that had received throughout the final battle, and in the film it took the explosion of a compressed air tank to kill it. The shark was resistant to bullets and harpoons fired at it from afar as well as knife attacks from up close. This shark was very resilient, however C. parvum is much stronger, so we are going to (figuratively) need a bigger boat. This microbe can survive in low to medium concentrations of chlorine in water and can cause a severe infection from only ten to thirty cells in a total of one hundred liters of water (6)! Drying out and freezing Cryptosporidium cells seems to work, but these actions can be hard to implement outside of a laboratory. C. parvum’s resistance makes real world solutions difficult to act on. Waterborne Cryptosporidium can easily slip through common water filters, making Cryptosporidiosis extremely hard to contain. This can lead to huge problems in urban environments and start outbreaks in a massive area. Imagine if a shark could escape Sea World through certain vents. If you can imagine this, you may have seen Jaws 3.
             A 35-foot long, 3-ton Great White Shark can be a major problem in terms of public health and safety if introduced to a rural beach community. If even a few C. parvum cells introduced into any public water system would be an outright catastrophe. Not only are these cells hard to kill, but they can also rapidly spread before being eradicated. In the end, the original Jaws’ kill count was about 8 people, however the final kill count of an outbreak of C. parvum could astronomical (depending on the community in which it attacks).
             The fictional shark created by Peter Benchley is a great example of just how dangerous a single living creature can be. Cryptosporidium parvum is even more dangerous due to its environmental resistances, incredible infectivity, and its tendency to hide within biofilms. The methods used to kill the shark in the films ranged from electric cables to magic technology used to drive the shark insane and impale itself (yes this happened, and yes it was incredibly stupid). As was mentioned before, freezing and drying out cells are clever methods to fighting microscopic attackers. As we further study these dangerous diseases, we may find unique and innovative ways to approach these cells from a place of safety. But if that fails, we can always just shoot the compressed air tank next to the water.

1. Fayer, R. & Ungar, B. L. Cryptosporidium spp. and cryptosporidiosis. Microbiol Rev 50, 458–483 (1986).
2. Hunter, P. R. & Nichols, G. Epidemiology and Clinical Features of Cryptosporidium Infection in Immunocompromised Patients. Clin Microbiol Rev 15, 145–154 (2002).
3. Flemming, H.-C. & Wingender, J. The biofilm matrix. Nat Rev Micro 8, 623–633 (2010).
4. DiCesare, E. A. W., Hargreaves, B. R. & Jellison, K. L. Biofilms Reduce Solar Disinfection of Cryptosporidium parvum Oocysts. Appl. Environ. Microbiol. 78, 4522–4525 (2012).
5. Koh, W., Clode, P. L., Monis, P. & Thompson, R. A. Multiplication of the waterborne pathogen Cryptosporidium parvum in an aquatic biofilm system. Parasites & Vectors 6, 270 (2013).
6. Carey, C. ., Lee, H. & Trevors, J. Biology, persistence and detection of Cryptosporidium parvum and Cryptosporidium hominis oocyst. Water Research 38, 818–862 (2004).

Jaws, Jaws 2, Jaws 3(D), and Jaws IV: The Revenge are owned by Universal Studios and was used under Fair Use as a commentary Cryptosporidium parvum.

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