Chapter 2: Terra Incognita Part 2

The body is a tough place to live, so I give the parasites credit. Usually organisms are made to live in a certain environment, like sharks in water or humans on land, but parasites are adapted to navigate though skin and muscle and through every organ of the body. They travel through the stomach and even as far as the Achilles tendon. They go anywhere they can be comfortable in their new host and they can feed on almost anything, from blood to snot to parts of liver, and they can even make their host's body deliver them food like take out Chinese food. It has taken scientists forever to study changes and behaviors in parasites, and they are still working on it.

A fine example of a traveling parasite, a parasite quite a far way from home, is "Trichinella spiralis". The nematode enters our system through undercooked pork, where it lives in cysts formed from muscle cells. When eaten, the parasite breaks free and swims to the intestines where it begins threading itself through the intestinal lining. Then it begins to reproduce and form cysts once again. The funny part is that the parasite doesn't even want to be inside you. It's cycle ends here and it's not happy with that. It really wants to be in a pig. Pigs die and are picked at by rats, which are then eaten by more pigs, so they cycle goes on and on from pig to rat to pig again. Each parasite has it's own dream host in which it can repeat it's cycle over and over again.

Trichinella spiralis

Michael Sukhdeo from Rutgers University in New Jersey was intrigued by the question "Why do parasites go where they go without having a brain or a map in their hands?" At first he assumed that they must be following a gradient, or scent, through the body like a shark does through water in search of blood, but this assumption proved to be wrong. He created a simulated host body out of tubes filled with liquids to simulate the digestive system and he tested the "Trichinella spiralis" parasite. He made sure to keep the tubes at body temperature and started adding chemicals that would be found in the system, but they did not react or reacted strangely to the chemicals, like they started moving violently when they were exposed to bile. Over time, he expanded his research to "Fasciola hepatica" or liver flukes. He built new chambers out of brass ad aluminum and used chemicals made by the liver to try and see if they were attracted to them. He got no response. He also tested their reaction to bile, and they to reacted violently. He finally realized where he
went wrong: he was seeing the parasites as free-living organisms and not as parasites. He

Fasciola hepatica

realized that they probably can't sense chemicals like a shark in the ocean because chemicals in the body have more restrictions, like they have to move around organs and through systems. He then wondered if the parasites navigate by reacting to different stimuli and through passed down, programed behavior. Plus, the circulatory system sort of pushes parasites in the right direction anyway. The parasites freaked out when they sensed the bile because they are usually at their destination before the bile or the bile disrupts their peace, so they are not drawn to it. The "Trichinella spiralis" is in the pig muscle when it reaches the stomach. Pepsin begins to break down the food they are in, which makes them start to go nuts and flail around. The meat then travels out of the stomach and into the intestines where they reach the bile and begin to calm down, The bile makes them begin to move like little snakes out of the meat and free into the intestines. The liver flukes move using a front sucker, or small set of teeth, and a sucker on their belly. They use these to both crawl and to crimp or spazz. The flukes start to twitch when they reach the bile in the intestines, this is when they begin to emerge out of the small intestine and crimp out of the abdominal cavity and make their way to the smooth abdominal muscles. The flukes then start creeping across the muscle at their own speed, knowing they are safe from the intestines force or any type of forceful liquids. They will almost always make it to the liver, one way or another. They don't need to know their up from their down or left or right to find where they need to go, they get there eventually. Who knew a parasite's sense of direction was so complex, but simple at the same time?