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?

Chapter 2: Terra Incognita Part 1

  

I am dedicating this post to the romantic "Schistosoma mansoni", otherwise known as the blood fluke. These little missile shaped parasites crawl out of the back of a snail living in a pond. They are in search of a human ankle to dive into, but when they feel the suns toxic Ultraviolet rays, they sink back into the shadows. As soon as the parasite senses human skin molecules in the water, they swim madly towards the source. Once they reach the ankle, they drop their tail and they release chemicals to soften the skin so they can cut through like butter. Hours later, the fluke reaches the capillaries, which are barely big enough to fit the fluke. The fluke rides through the blood, through wide vessels and small vessels, heavy currents and weak ones, and ends up in the lung capillaries, where it then goes to the arteries and veins and starts its journey all over again. The flukes do this 3 times before they finally settle down in the liver and begin feeding on the hosts blood. They start developing their respective reproductive systems for either a male or female. Their reproductive systems mature in 12 weeks and they start looking for mates. Males are shaped like canoes and females are slender, and the males let out chemicals to attract the females. The happy couple lock together, move toward the large intestine, and stay there for the rest of their lives. The male takes in blood to feed himself, but he ends up caring for his mate and ends up giving most of his food to them. This species of parasite is one of the most monogamous organisms out there. Males even stay attached to females after the female has died. Scientists have also found homosexual parasite couples locked together, although their fit isn't as tight. Even when scientists separate them, they end up joining back together again. The couple of flukes mate everyday until the female is ready to lay her eggs, which then the male takes he and his female to a suitable spot. Most of the laid eggs stay in the bowl and exit the host, wanting to get out and find a new snail to invade, but some eggs are carried away by the bloodstream to the liver and cause the painful inflammation linked with shistosomiasis. And they lived happily ever after...

Chapter 1: Nature's Criminals Part 3

The question of how parasites got into the body in the first place or how are they made was still floating around when a new question was added to the pile: what do baby flukes look like? I mean, every organism is born and looks like their parent did as they grow up. But what about parasites? Well Danish zoologist Johan Steenstrup answered this question in the 1830's. He saw fluke-like animals with long tails swim towards snails and make cysts on the insides of their shells. He opened those cysts to discover adult flukes! He found that parasites may travel in one form, but grow into another. With this in mind, and knowing that the snail caries many different "types" or parasites in its body, he figured that the different types of parasites may actually be the same parasite, just in different stages. He proved that spontaneous generation is incorrect and that parasites move from host to host in different forms. These discoveries made other biologists start looking back at parasites and looking at their similarities.

In the 1840's, a German doctor named Friedrich Kuchenmeister added to this discovery. He found that some parasites developed in one part of an organism, but ended up moving to somewhere else in the body to live out it's life. He took bladder worms, the worms Aristotle saw on the pig tongue, and fed them to other animals, believing that these worms and tapeworms were related. He was right. When he opened up the animals later, he found that the bladder worms had moved down to the digestive tract and had grown into adult worms. He even tested this theory on human prisoners sentenced to be killed. He fed them food with the bladder worms in it and months later, after they were executed, he opened them up and saw the tapeworms.

Louis Pasture did studies with broth to prove that bacteria did not spontaneously generate. This launched a better study on bacteria, and scientists found that bacteria was not a parasite like people previously thought. German scientist Robert Koch made rules for classifying bacteria: they had to be associated with a disease and they had to be isolated and grown in a pure culture. Parasites can do none of these things. Protozoa, which is a form of parasite, are more like the cells in our bodies. Bacteria are just sacks of DNA, but protozoa have DNA contained in a nucleus and they have compartments dedicated for making energy and other things they need to function. Using this, scientists divided life into prokaryotes (bacteria) and eukaryotes (protozoa, animals, plants, and fungi). Soon after, scientists found that many fevers and illnesses, like malaria, were not caused by bad air or our own bodies, but by parasites.

Malaria Parasites In Red Blood Cells

Chapter 1: Nature's Criminals Part 2

People soon realized that there wasn't only one type of parasite, there was a multitude of different kinds. They had discovered that there were visible and invisible parasites! These little bad boys varied in oddities, like some had horns, weird tails, what looked like hair, and some even resembled lizards and little frogs. In 1673, a shopkeeper from Delft put rainwater under a homemade microscope and saw crawling little globs, some with odd shapes and tails. This man was Anton van Leeuwenhoek and he was the first man to visually see bacteria. He put everything from rain water to his own stool under the microscope just to observe these little creatures and the way they move. Many tiny parasites were discovered, but more visible parasites were discovered too.

Leeuwenhoek's Microscope

Even after all of this discovery, scientists still believed that parasites were still generated by the host. People didn't know better and they figured that since the parasites had no way to get into the body, they must have been created by the body. They figured that these parasites had never been out of the body and they had hooks and tails for living in the body, but were not fit to survive outside of it. Scientists found parasites in animal fetus's and all over and animals body, but how in the world would they get in there?

The belief of spontaneous generation contradicted what the bible said, that everything was made by God in a week and nothing could worm its way into being a new organism. Zimmer worded it "If our own blood could spontaneously generate life, what help did it need from God back in the days of Genesis?" (pg. 5) So a new question was raised: Why would God create such creatures, and when were they created? One of my favorite passages from this chapter pertains to this question. Zimmer said "Why did God create parasites? To keep us from being too proud, by reminding us that we were merely dust. How did parasites get into us? They must have been put there by God...Perhaps they were passed down though generations within our bodies to the bodies of our children. Did that mean that Adam, who was created in purest innocence, came into being already loaded with parasites? Maybe the parasites were created inside him after his fall. But wouldn't this be a second creation, an eighth day added on to that first week-"and on the following Monday God created parasites"? Well, then, maybe Adam was greeted with parasites after all, but in Eden parasites were his helpmates... But why should Adam, created not only in innocence but in perfection, need any help at all?"(pg. 5) Now you can see why the people of these times were so confused.

Chapter 1: Nature's Criminals Part 1

The word "parasite" comes from the Greek word "parasitos", meaning "beside food". They were reffering to the people who served food to nobles or ammused nobles in order to gain a favor or get a few scraps of food when they came up with this. These people leached off of other people, or lived off of other people. Sound formiliar? The Greeks also looked at parasites in terms of biology as well. As a matter of fact, Aristotle saw things that lived on on a pig's tounge. But basically every culture knew about parasites in one way or another and they had their own plants and treatments to get rid of them and guidelines to help ward off the beasts. We may not realize it, but many of the stories we heard as children may actually be caused by parasites. Guinea worms may be those "firey snakes" that plagued Israelites in the Bible. The worms were frequent in the place he traveled. They travel up the leg and do make a person feel like flames are licking their skin, caused by the immunes responce to the worms. The only way to remove these worms is to slowly wind them up on a stick. Think about it- Stick and "firey surpants". This procedure may have given birth to the modern day medical symbol, two snakes winding themselves around a stick.

Durring the Resaissance, European doctors didn't really think parasites caused illness. They thought that diseases caused the body to go out of wack or they were sick because of the heat or the cold. They thought that malaria was caused by breathing in bad air. They also belived that a diseased body produced it's own parasite, not the other way around. They thought that since parasites were living things, they MUST be produced by the body. Scientists thought that they were spontaniously generated in the blood.

Tapeworms, Sleeping Sickness, and River Blindness

I described River Blindness, Sleeping Sickness, and Tapeworms in previous blog posts, but seeing is beliving, so here are a few videos describing people who had been diagnosed with these parasites.

River Blindness:

Sleeping Sickness:

Tapeworms:

The Prologue Part 2

After his trip to Tambura, Zimmer traveled to the jungles of Costa Rica with many other biologists, but one man stuck out in particular, a Mr. Daniel Brooks. The man really didn't look like a biologist, sporting aviator glasses and a jogging suit and rocking a large drooping mustache. As the biologists walked in the jungle, the man collected and bagged frogs and toads of many kinds and carried them in his pocket. Brooks took the frogs back to his lab, which consisted of a shed with chicken wire walls, to see what he had specifically found. He took a frog that he had collected out of a bag, struck it on the edge of his lab table, and got ready to dissect it. There were a multitude of parasites in the frog, from filarial worms to flukes, coming from every orifice of its body, like the lungs and even the ear canals. Brooks had seen a lot of parasite over the years in all kinds of places, from iguanas with tapeworms to nematodes in a deer's Achilles tendon. Brooks estimates that he had seen about 11,000 parasites and had identified 300 of them. Every organism has at least one parasite living along side it, whether they notice it or not. Some parasites even have their own parasites! And even those parasites may have parasites too! Scientist may not know a lot about parasites, but they do know that parasites make up the majority of species on earth. Parasites may even out number the number of species on Earth 4 to 1. It's basically a parasites world and we're just living in it. Zimmer made the statement "...the study of life is, for the most part, parasitology..." and now I can see why.