On Pages 95-97 in chapter 5, Dr. Moalem describes a parasitic organism known as the Guinea worm or Dracunculus medinensis. This worm has evolved in relation to humans to a point where its larvae are not destroyed by the human digestive system. Additionally, when a female Guinea worm exits its human host in order to reproduce, it excretes an acid that burns an exit tunnel to the surface of the host's skin. This acid causes a burning sensation which causes the human to seek water which allows the worm to spread its progeny through the release of a milky fluid containing thousands of larvae. This relates to Big Idea 4: Biological systems interact, and these systems and their interactions possess complex properties.
Research if and how the Guinea worm and other parasitic organisms influence their host's behavior to better survive and reproduce. Also research what selective advantages could a parasite gain from infecting a specific host; for example, what selective advantages are there for Hymenoepimecis argyraphaga wasp to infect the Plesiometa agyra orb-weaving spider as opposed to, say, a human. Then, explain your findings and describe possible actions that can be taken in order to reduce the spread of these parasites OR describe why actions should NOT be taken to reduce the spread of these parasites.
-Chris Yao, chyao4@students.d125.org
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ReplyDeleteGuinea worms use humans to increase chances of surviving and reproducing by making a human host feel a burn, so the host will seek water. Going to water will trigger the worm to spread larvae to infect more water, so more human hosts are infected. The process will continue as long as the larvae get deposited into a water source by the human host because of the burning. An article called "Parasite Influence on Host Behavior - Part 1" describes how another parasite Toxoplasma sexually reproduces in the gut of cats.(http://www.boloji.com/index.cfm?md=Content&sd=Articles&ArticleID=5853) The cysts of toxoplasma are released in the feces, and eaten by mammals like rats. The toxoplasma changes the rat's behavior, making the rat lose its natural fear of cats. Then, the rat will be consumed by the cat, and the cycle of toxoplasma reproducing is repeated. The use of a host is the way the parasite survives and reproduces. The parasites need a way to be able to find another parasite to sexually reproduce with, and the method of influencing a rat to get eaten by a cat easier to find another parasite helps a parasite reproduce. “How Common 'Cat Parasite' Gets Into Human Brain and Influences Human Behavior” from Science Daily describes that when the parasite enters humans, there are mild flu -like symptoms before the parasite enters a dormant stage.(http://www.sciencedaily.com/releases/2012/12/121206203240.htm) The toxoplasma parasite brain and manipulates the host by taking over one of the brain's neurotransmitters. In studies, dendritic cells, which are a key component of the immune system, started secreting the signal substance GABA.GABA is a signal substance that inhibits the sensation of fear and anxiety.Many studies can confirm that mental diseases like schizophrenia, depression and anxiety syndrome are common in people affected by the toxoplasma parasite.
ReplyDeleteThis relates to big idea 3 ( Living systems store, retrieve, transmit, and respond to information essential to life processes). The parasite infects the behaviour of both rats and humans. In rats, the rats don’t respond naturally and do not have their natural fear of cats. The animal has sensory organs to detect and process the external information, but just doesn’t respond correctly. In huimans, cell signaling is used by the parasite to inhibit the sensation of fear and anxiety. The cell signaling pathways are affected in humans, and the signals build up to affect complex behaviours that affect physiological response in the organism.
A toxoplasma parasite manipulating a rat host is a selective advantage because rats are around waste and find food in waste, and are also easy prey for cats, where the parasite reproduces. The use of the rat makes the parasite easy to be transferred from rat to cat because a cat will always want to eat a rat for food. Another example is that a Hymenoepimecis argyraphaga wasp infects the Plesiometa agyra orb-weaving spider instead of something like a human because the spider can weave a web to protect the wasp's offspring. Infecting a human wouldn't do too much use because humans can’t produce a silk barrier like the orb-weaving spider can. This relates to Big Idea 1 ( The process of evolution drives the diversity and unity of life), where the parasite survives and reproduces easier by using rats and cats. Due to to the toxoplasma parasite being a more favorable phenotype, it has survived to this day in the competitive environment while many other parasites haven’t survived to this day because their phenotype was a selective disadvantage. This is also seen when the Hymenoepimecis argyraphaga wasp infects the Plesiometa agyra orb-weaving spider because the spider can provide a web protection for the wasp’s offspring. The relationship benefits the wasp’s offspring so the species is favored in a competitive environment because the offspring have a higher chance of surviving to reproduce with the help of the orb spider’s web.
I think that the spread of parasites can't really be stopped too easily. Guinea worms already are almost stopped by spreading knowledge of dealing with them like not seeking water when feeling the burn to stop the spread. However, it's hard to stop a Hymenoepimecis argyraphaga wasp from infecting an orb spider somewhere in an environment. The populations of those species are too big to stop the parasites from spreading by manipulating a host's behavior. We could stop the spread of the toxoplasma by cleaning up more cat feces to prevent a rat from consuming it to become infected. Overall though, while it is nice for us to stop parasites like Guinea worms, the spread of many parasites can't be stopped because of the number of them that exist.
ReplyDelete(Eric Huang - ehuang4@students.d125.org)