April 17, 2015

By Medical Discovery News

It’s easy to think that nothing good could come from a disease that killed millions of people. But Dr. Pat Shipman, an anthropologist at Pennsylvania State University, disputed that notion in his recent article in “American Scientist,” where he suggested the Black Death that ravaged Europe in the Middle Ages may have resulted in some positive effects on the human population. Considering that we are in the midst another significant plague (the Ebola virus in West Africa), we could certainly use more information about the role of pandemics on human populations.

The Black Death or Bubonic plague started in the mid-1300s and was caused by a bacterium called Yersinia pestis, which typically enters the body through the bite of a flea. Once inside, the bacterium concentrates in our lymph glands, which swell as the bacteria grow and overwhelm the immune system, and the swollen glands, called buboes, turn black. The bacteria can make their way to the lungs and are then expelled by coughing, which infects others who breathe in the bacteria. The rapid spread of the infection and high mortality rates wiped out whole villages, causing not only death from disease but starvation as crops were not planted or harvested. It killed somewhere between 100 million to 200 million people in Europe alone, which was one-third to one-half of the entire continent’s population at the time. The plague originated in the Far East and spread due to improved trade routes between these two parts of the world.

Today, global travel is easier than ever thanks to extensive international airline networks. Just like with the Black Death, our transportation systems could enhance the spread of a modern plague. Of course, modern healthcare is also more sophisticated and effective, but as the latest Ebola outbreak has reminded us, a pandemic is a realistic possibility.

Dr. Sharon DeWitte, a biological anthropologist at the University of South Carolina, recently made several discoveries from comparing the skeletal remains of those who died from the Black Death and those who died from other causes during the same era. First, she found that older people, who were therefore already frail, died at higher rates. Killing this group at a higher rate created a strong source of natural selection, removing the weakest part of the population.

After the plague years, she found that in general people lived longer. In medieval times, living to 50 was considered old age. But the children and grandchildren of plague survivors lived longer, probably because their predecessors lived long enough to pass on advantageous genes. Today, a genetic variant in European people called the CCR5-D32 allele, which was favored during the natural selection initiated by the plague, is associated with a higher resistance to HIV/AIDS.

Microbes have an intimate relationship with human populations and have shaped human evolution through the ages. We may see survivors of the Ebola virus passing on similarly advantageous genes through natural selection as well.

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