Class blog for sharing and commenting on current events in biology.

Monday, December 10, 2012

Deciphering the Tools of Nature's Zombies


Kylie Kardos                                                                                                    December 10, 2012
Core Biology 1 Honors                                                                                   C-odd, Davies
Current Event Report: Deciphering the Tools of Nature’s Zombies
Zimmer, Carl. “Deciphering the Tools of Nature’s Zombies” New York Times Online. 5 December 2012.
            Scientists have recently found research regarding how parasitic invaders are able to manipulate particular hosts in nature. Viruses, fungi, protozoan’s, wasps, tapeworms, and many other parasites in nature are able to control the brains of their hosts. Deep within the Costa Rica rain forests, a species of spider called Anelosimus octavius lurks around, displaying peculiar and creepy behavior that is a significant part of its normality. These spiders will create a drastically different web than their own for the parasitic wasps living inside of them. Nothing like the spider’s typical web, this web contains a platform with a thick sheet to shield it from the rain. The wasp larva then wriggles to the edge of the platform and spins a cocoon that hangs through an opening kindly provided for the parasite by the spider. These wasps are able to manipulate their hosts into carrying out certain actions like this. When the spider finally dies, with its brain completely taken over by its parasitic invader, out will come the wasp’s larva. Scientists have been researching the process of how these parasitic invaders are able to manipulate their hosts, and they have recently made some remarkable discoveries. In order for the wasp to manipulate the spider, the wasp must have genes that create proteins that alter spider behavior. Recently, scientists have been able to identify this gene in several types of species, such as the baculovirus, which is a virus scattered on leaves in forests and gardens. Luckily for humans, this virus is only dangerous for caterpillars of insect species. When the caterpillar eats a baculovirus-laden leaf, the parasite intrudes on its cells and replicates, manipulating the caterpillar to “climb high.” Once the caterpillar is high in the trees, its body will dissolve, thus launching the viruses on potential hosts below. David P. Hughes of Penn State University has discovered that a single gene referred to as egt is what causes the caterpillars to climb up trees. Egt contains an enzyme, which kills a hormone that signals a caterpillar to stop eating and molt. Dr. Hughes believes that this virus prompts the caterpillar into a “feeding frenzy,” as commonly, gypsy moth caterpillars will come out at night to feed and will then reside near the bottom of trees to hide from predators. However, the zombie caterpillars will continuously search for food.
            Many other parasites manipulate their hosts by moving the neurotransmitters inside their brains. This is how thorny-headed worms send their hosts, which are shrimplike crustaceans known as gammarids, to their death. Gammarids live in ponds, so they usually dive deep into the mud when they feel threatened. However, an infected gammarid will race up to the surface of the pond and will then hang on to an object such as a rock or stem. As baculoviruses go from caterpillar to caterpillar, thorny-headed worms must live in two species - a gammarid, and then a bird. Simune Helluy of Wellesley College researched this suicidal reversal, discovering that the parasites control the gammarid’s brain through its immune system. The parasite creates a strong response from the gammarid’s immune cells, which then set loose chemicals that destroy the parasite. The parasite blocks these attacks and the hosts’ immune system creates a swelling that attacks its own brain. There, it interferes with the brain’s chemistry, producing large amounts of the neurotransmitter serotonin, which influences how neurons transmit signals. Dr. Helluy believes that the rush of serotonin triggered by the thorny-headed worms corrupts the signals traveling from the eyes to the brain. Usually, the threatened gammarid is attracted to the darkness at the bottom of its pond to protect itself. Researchers believe that thorny-headed worms cause their hosts to recognize sunlight as darkness, therefore swimming upwards instead of downwards.
            This article is significant to society because based on the research scientists have gotten and are in the process of getting, we can figure out whether or not humans are prone to being manipulated by parasitical creatures in nature. For instance, some studies have shown that humans can become hosts of Toxoplasma gondi, a single-celled parasite that reproduces in the guts of cats, which shed it in their feces. Humans can become prone to this if they handle contaminated cat litter or if they eat parasite-laden meat. By learning about the process of how these parasites are able to fully take over certain creatures, we can prevent this from happening in the future and can possibly cure certain disorders. According to the article, ‘Dr. Adamo, the co-editor of the journal’s new issue, thinks that this new science of “neuroparasitology” can offer inspiration to pharmaceutical companies that are struggling to find effective drugs for mental disorders.’ “A number of the big companies have given up on their neuroscience labs,” she said. “Maybe the parasites can teach us something.” I chose this article because after just reading the headline, I was immediately captivated and could not stop reading. I think the whole topic of parasites taking over hosts is really fascinating. Before reading this article, I was unaware that that this phenomena was occurring in the world and if someone had told me that there were such thing as zombies in nature, I can honestly say that I definitely wouldn’t have believed them.
            I thought that this article was extremely well written. Although it is long, I found myself hooked throughout the entire article. I believe that there is plenty of evidence that backs up all the points the author makes. I enjoyed learning about all three of the processes that were described in this article in which the parasites took over the three hosts, and I found all to be described well. My only criticism for this article is that I wanted to know more about what would happen if humans were invaded by a particular parasite species and whether or not that could be treated or prevented. One particular point I found to be important was how the author states that, “The way that a parasite goes about changing behavior is not the way a neurobiologist would do it.” Evidence in the article provided that ‘a typical drug focuses on only one type of molecule in the brain while parasites often launch a more broad attack that still manages to cause a specific change in their host.’ Ultimately, though, I enjoyed reading this article, and it left me wanting to know more about parasites and zombies in nature.

1 comment:

  1. The article Deciphering the Tools of Nature’s Zombies that Kylie Kardos reviewed is very interesting, and Kylie did a great job analyzing it. On top of describing what happens when a parasitic invader manipulates its host, she also explains how it is able to do such a thing. For instance, with the example of how thorny-headed worms control their hosts, shrimplike crustaceans called gammarids, Kylie discusses how the worms do so through influencing how the host’s neurons transmit signals, interfering with its brain’s chemistry. In response to worms in their body, the gammarid’s immune system tries to kill them with a chemical that the worms end up blocking, ultimately backfiring to attack the host’s brain. Because of this, large amounts of the neurotransmitter serotonin are produced, affecting the signals traveling from the eyes to the brain of the gammarid. The gammarid is then tricked into swimming upwards to the surface of a pond where it becomes a better target for preying birds, the second species the worms must live in. Kylie again did this well for explaining how when caterpillars are infected with baculovirus, this parasite forces the caterpillar into a “feeding frenzy” through a gene known as egt. This results in the caterpillar climbing high into trees in a constant search for food, leading to its death. Another thing Kylie did well was relating this “zombification” to humans and using this to incorporate how it works with cats. She did this by saying humans can become hosts of Toxoplasma gondi, “a single-celled parasite that reproduces in the guts of cats,” by handling contaminated cat litter or eating meat with parasites in it. I really did find all of this article to be interesting. It’s hard to believe that there is such a thing as zombies in nature! It was so cool to learn that a parasitic wasp can control its spider host into building it a web that will eventually serve as its home after the spider dies. I also found it interesting that scientists could perhaps use what they learn from parasites for creating medicines to treat mental disorders, trying to mimic the way the parasites change the behavior of their host. One piece from the article that could have been included is how “zombified” rats can become less fearful of cat order when infected with Toxoplasma, “potentially making them easier prey to catch.” However, the review is long enough as it is and the examples provided are plenty for the reader to get the idea. Overall, Kylie’s review is very well-written and informative.

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