Dr. Sharon Moalem
explains about a parasitic worm that humans have battled for years, the Dracunculus
medinensis (or the Little Dragon), on pages 122-123. D. medinensis use a human victim to
grow, and this relates to Big Idea 2, biological systems utilize free energy
and molecular building blocks to grow, reproduce, and to maintain dynamic
homeostasis.
How does the Dracunculus
medinensis enter the human body, grow over the years and reproduce? How
does a parasite, like D. medinensis, use host manipulation? Cite a
source to explain how the Carter Center managed to lower the cases that D. medinensis cased. How would you
predict that the D. medinensis will adapt?
(Lily Barghi lbarghi4@students.d125.org)
Dracunculus medinensis first enters the human body when a human drinks unfiltered water containing copepods, or small crustaceans, infected with D. medinensis larvae. Once ingested, the crustaceans die, while the larvae travel down into the small intestine. They penetrate the intestinal wall, and they eventually make their living in the abdominal cavity. Approximately one hundred days after, the larva will begin to molt, mature, and mate.
ReplyDeleteWhile the males are broken down by the body, females carrying fertilized eggs must find a way to manipulate the host into getting their larva into the water, where the larva can develop into its infectious stage. The parasite's method of doing this is by traveling to the surface of the host's skin, resulting in the blisters that are the symptoms of infection; since the host will most likely travel to the water to relieve the pain, this gives the opportunity for the female parasites to escape and release the larva. Once released, the stage 1 larva are eaten by the copepod, allowing the larva to develop into its stage 3 infectious stage, waiting for a human to ingest the crustacean and repeat the cycle again.
The Carter Center's strategy in eradicating the D. medinensis parasite is through public education to prevent contamination, supplying millions of water filters, applying chemical treatments to contaminated water, and supplying uncontaminated water from underground. (http://www.cartercenter.org/health/guinea_worm/mini_site/videos.html) One possible problem with this method may be that certain parasites resistant to chemical treatments may survive and reproduce while the non-resistant parasites die off, leading to the overall development of an adapted chemically-resistant population of D. medinensis - similar to how certain disease strains adapt and become resistant to antibiotics. However, D. medinensis, unlike bacteria, do not have the advantage of rapid mutation and growth, leaving them powerless against such a rapid and effective campaign against the parasite. As a result, the number of cases have dropped all the way from 3.5 million in in 1986 to 542 in 2012, leaving D. medinensis all but completely eradicated. (http://www.cartercenter.org/health/guinea_worm/mini_site/index.html)
(Matthew Zhang: mzhang4@students.d125.org)