Dr. Sharon Moalem begins exploring the correlation between disease and evolutionary responses with the example of hemochromatosis. Hemochromatosis is a hereditary disease that results in too much iron in the body. Dr. Moalem identifies the irony in the disease that causes a body to harm its own organ with iron buildup, but may also protect a body from bacterial infection. He attributes the survival of some Europeans during outbreak of bubonic plague to this disorder (Moalem 15). The bubonic plague would have thrived in nonhemochromatic persons because they did not possess the "iron-locking response" that leaves macrophages without much iron (Moalem 12).
The bubonic plague is an example of a specific event in a population causing evolutionary change (Big Idea 1). The bubonic plague was caused by Yersinia pestis (Moalem 9) that targets the lymphatic system. The lymphatic system emcompasses the lymph nodes, where the iron rich macrophages bring back the bacteria (Moalem 12). This would explain the swelling of the lymph nodes in a patient with the bubonic plague.
The bubonic plague was so widespread that it caused hemochromatosis to be favored in Europe during the Dark Ages causing evolutionary change and creating a population with higher occurence of hemochromatosis (Big Idea 1). However, Dr. Moalem also recognizes that other diseases causes by bacteria have ravage human populations since the bubonic plague, like tuberculosis (Moalem 21). Other pandemics, like the cholera epidemic of 1821 and the 7 outbreaks after, were caused by bacterial infection (Suddath, Claire. "Top 10 Terrible Epidemics." Time. Time, n.d. Web. 11 Mar. 2013.). Recently cholera has returned and devastated communities in Haiti (Steinlechner, Benjamin. "At a Glance: Haiti." UNICEF. N.p., 1 Nov. 2010. Web. 11 Mar. 2013.).
What is the difference between the bubonic plague and other epidemics in the selection for hemochromatosis? Research one of the bacteria that caused the bubonic plague, tuberculosis, and cholera. What body systems do the bacteria target? Are they all dependent on the iron in the human body? How widespread was each disease? What populations did each disease affect? Would a person with hemochromatosis react differently to the bacteria than a normal person?
(Katelyn Noronha knoronh4@students.d125.org)
Yersinia pestis is the bacterium that causes the bubonic plague. Their life cycle includes infecting a flea. The flea then goes on to infecting rats by biting them, then the rats go around infecting humans, and thus a plague is started and the disease spreads through human contact(1). The bubonic plague targets the lymph nodes and the white blood cells that live there. Since the bubonic plague loves iron, people with hemochromatosis would be able to survive a bubonic plague.
ReplyDeleteThe bacterium that causes tuberculosis is Mycobacterium tuberculosis. The bacteria require plenty of oxygen to survive thus thriving in your respiratory system. Because of its fatty coating, the bacteria have a slow growth rate. Tuberculosis is an airborne illness, and the bacteria are spread through coughing (2). The disease can be caught any where, but it is most commonly diagnosed in Sahara. Africa and Southeast Asia. A person with hemochromatosis wouldn’t react differently to the bacteria since iron is as needed as oxygen.
Cholera is caused by the bacterium Vibrio cholerae. This bacterium is spread through contaminated water, and the victim is left dehydrated and has an electrolyte imbalance. The bacteria targets your intestines, and fights with the flora or good bacteria. The “bacterium's defense involves attaching one or two small amino acids to the large molecules, known as endotoxins, that cover about 75 percent of the bacterium's outer surface.”(3) This creates armor for the bacterium and thus it is harder for our immune system to fight Cholera. But with the right antibiotic, the bacterium can be defeated. It was found in a study that Cholera thrives when iron is present in the enviornment (4). Cholera affects populations with poor water sanitation and sewage problems, like Haiti and India. A person with hemochromatosis infected with cholera would be able to recover faster then a person with out the disease, since cholera is able to thrive with iron present.
1) Yi-Cheng Sun, B. Joseph Hinnebusch and Creg Darby Proceedings of the National Academy of Sciences of the United States of America , Vol. 105, No. 23 (Jun. 10, 2008), pp. 8097-8101
2) VIB. "'Missing link' discovered in defense mechanism of tuberculosis pathogen." ScienceDaily, 14 Nov. 2012. Web. 17 Apr. 2013.
3) University of Texas at Austin. "Fifty-year cholera mystery solved." ScienceDaily, 29 May 2012. Web. 17 Apr. 2013.
4) Patel, Mrudula, and Margaret Isaacson. "THE EFFECT OF IRON ON THE TOXIGENICITY OF VIBRIO CHOLERAE." American Journal of Tropical Medicine and Hygiene 60.3 (1999): 392-96. Web. .
Anna Podber
(apodber3@students.d125.org)