The Plague: It was the Gerbils

Aug. 7, 2015

By Medical Discovery News

In the past 800 years, many things have been blamed for the plague that swept through Europe in the Middle Ages: the alignment of the planets, bad air, lack of proper hygiene, black rats, and their fleas. Now scientists have data that suggests the climate in Central Asia at that time influenced the size of the great gerbil population, which triggered cycles of plague in Europe. These furry little rodents carried the plague bacterium, as did the fleas that fed on them. When the gerbil population shrank, the fleas found alternate hosts like horses, humans, and eventually rats, which then made their way to Europe and triggered the plague pandemics.

The plague was caused by the bacterium Yersinia pestis. It is transmitted to humans through the bite of a flea that has fed on an infected rodent. Plague outbreaks have afflicted humans for thousands of years and changed the course of history. The first recorded plague pandemic began in 541 and was named the Justinian Plague after the 6th century Byzantine emperor. Frequent outbreaks for the next 200 years are likely to have killed over 25 million people. The second pandemic, called the Great Plague or the Black Death, began in China and spread westward along trade routes to Constantinople and into Europe. About 60 percent of Europeans died, eliminating entire towns.

The third pandemic, or Modern Plague, also began in China and spread to Hong Kong by 1894. Rats hitching rides on steamships spread the plague to port cities around the world for the next 20 years, killing about 10 million people. By then scientists were able to identify the bacterium responsible and how it spread. Efforts to control the rat population eventually ended the pandemic. It continued to infect people (although in much smaller numbers than before) during the 20th century, such as in Vietnam during the war. The bacterium is still in the reservoir of wild rodents, and today most cases of plague are in sub-Saharan Africa and Madagascar. The plague can be effectively treated with common antibiotics, but if left untreated it has a high mortality rate.

Since there are still lots of rats in Europe, some wonder, why is there no plague? Researchers proposed that each time, the plague actually started in Asia. To test their theory, they examined climate records using the rings of trees. The incidence of plague did not correlate with climate changes in Europe, but it did with changes in Asia. It was already known that the Asian great gerbil carries Yersinia pestis, and when the weather in Asia was good, gerbils thrived, but when it turned bad, their population would crash. Then their fleas would seek another host such as human traders and their pack animals, who spread the plague to other parts of the world. They found no evidence that rodents in Europe carried Yersinia pestis, so that would explain why cases of the plague disappeared between pandemics.

So don’t worry about the little gerbils in the pet store – they are not carrying the plague.

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The Bright Side of Black Death

April 17, 2015

By Medical Discovery News

Bright Side of Black Death

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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Down Syndrome in the Middle Ages

Jan. 30, 2015

By Medical Discovery News

Down syndrome is likely as old as humans themselves, but a recently discovered skeleton of a girl who died 1,500 years ago in France is the oldest confirmed case. The way she was buried seems to indicate that she was not scorned during her life and death in the Early Middle Ages.

Down syndrome, also called Trisomy 21, arises when a person is born with three rather than two copies of chromosome 21. It occurs in one out of 691 babies born in the U.S., making it the most common genetic disorder. Every person with Down syndrome is unique and has different levels of physical and intellectual abilities. The most common physical signs are upward slanting eyes, flattened facial features, ears that are small or unusually shaped, broad hands with short fingers, and a small head.

Other, more serious complications can include poor muscle tone, heart problems, problems swallowing, blockages in the intestines, cataracts or crossed eyes, hearing loss, increased susceptibility to infections, a less-active thyroid gland, and a higher risk of developing leukemia. People with Down syndrome develop dementia at a younger age than the general population. Their intelligence ranges, but with therapies, many Down syndrome children grow up to have jobs and live independently.

The chance of giving birth to a baby with Down Syndrome increases with the mother’s age, from 1 in 1,000 at age 30 to 1 in 100 at age 40. The American College of Obstetrics and Gynecology now recommends that all pregnant women be offered a prenatal screening test for Down syndrome, which is 99 percent accurate.

For centuries, people with Down syndrome have been part of art and literature. It wasn’t until the late 1800s that an English physician named John Langdon Down published the first accurate description, calling the condition “Mongolism.” The modern term Down syndrome became the accepted term in the early 1970s. The cause of Down syndrome, Trisomy 21, was discovered by French pediatrician and geneticist Jerome Lejeune, although Marthe Gautier, a retired pediatric cardiologist and scientist from Paris, now claims she did most of the experimental work that led to the discovery of Trisomy 21.

This newly discovered skeleton, which is the oldest case of Down syndrome found thus far, was unearthed near a church in a fifth- and sixth-century necropolis in Saône-et-Loire in eastern France. The five- to seven-year-old girl exhibited a short, broad skull, flattened skull base, and thin cranial bones, all features of Down syndrome. She was buried on her back with her head in a westerly direction, similar to the 94 others buried there. The archeologists believe that since she wasn’t treated any differently in death, it’s unlikely she was stigmatized when she was alive. But researchers must uncover further details about Down syndrome in the Middle Ages to know more about how she may have lived.

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