Ahira's Hangar

I've always found the bubonic plague a morbidly fascinating subject. I saw a show on History Television a couple of years ago - don't recall the title - that examined the Black Death from a point of view similar to what that study says, that the disease did not kill everyone who came into contact with it.

I wish I remembered more, but basically the program focused on a certain percentage of people who remained healthy despite being in the middle of the plague. The hypothesis was that their immune systems had something extra that allowed them to defy the disease. The really interesting part: the idea that maybe there is a connection between these people from long ago and certain people today who seem to be able to defy AIDS (and perhaps other diseases). I hope I remembered all that correctly.

Return of the Plague
Tuesday, Feb. 12, 2008 By LAURA BLUE Related Articles
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Yet the plague is not just a disease of the distant past. While cases tapered off in the mid-20th century, the World Health Organization (WHO) now classifies plague as "re-emerging." No one is predicting another pandemic like the Black Death that devastated Europe. The WHO now records at most only a few thousand cases worldwide per year; and, if detected early, the disease can be treated effectively with antibiotics. But since the early 1990s, plague has returned to places — including India, Zambia, Mozambique, Algeria and parts of China — that had not seen it in many years or even decades. Its global footprint has also shifted, according to a paper published last month in the journal PLoS Medicine. In the 1970s, most plague cases were in Asia; today, more than 90% are in Africa. The conundrum for epidemiologists: Why is human plague reappearing now, even though nearby animal populations have likely harbored the culprit Yersinia pestis bacteria all along?

Plague lives in many rodent species, and is most often transferred to humans by the animals' fleas. Scientists know which regions of the world harbor infected animals, but they are only just beginning to understand the dynamics of plague infection. Its spread depends not just on Yersinia pestis but also on interactions among rodents and, crucially, on contact between humans and wildlife. Madagascar is a good example. For decades, plague was restricted to the highlands, according to a 2004 paper by researchers in Madagascar, Senegal and France. But it showed up on the coast in 1991, when the Asian shrew somehow picked up infected fleas. The plague's earlier comeback in the inland capital, Antananarivo, arose as city sprawl and shoddy housing put residents in closer contact with black rats. In 1998, inland villages reported cases, too, perhaps caused by rats displaced through deforestation.

Even in the antibiotic age, then, containing plague requires monitoring more than human cases, says Nils Christian Stenseth, head of the Center for Ecological and Evolutionary Synthesis in Oslo, and lead author of the PLoS Medicine paper. Working with nearly 50 years of animal, human and bacteriological statistics from the former Soviet Union, his team found that human plague in Kazakhstan occurs only when the local gerbil population reaches a certain threshold in winter. Warmer winters mean more gerbils. That, says Stenseth, suggests plague's "re-emergence might have a climate component."

If so, global warming may exacerbate the threat — an unsettling thought, given the viciousness of the disease. "The plague bacillus is probably the most pathogenic infectious agent on the planet right now, and we still don't know why it's so virulent," says Elisabeth Carniel, a plague expert at the Institut Pasteur in Paris. It may no longer make history, but plague hasn't lost its terrifying power.

Out Of Africa -- Bacteria, As Well: Homo Sapiens And H. Pylori Jointly Spread Across The Globe
ScienceDaily (Feb. 16, 2007) — When man made his way out of Africa some 60,000 years ago to populate the world, he was not alone: He was accompanied by the bacterium Helicobacter pylori, which causes gastritis in many people today. Together, man and the bacterium spread throughout the entire world. This is the conclusion reached by an international team of scientists led by Mark Achtman from the Max Planck Institute for Infection Biology in Berlin, Germany. The researchers also discovered that differences developed in the genetic makeup of the bacteria populations, just as it did in that of the various peoples of the world. This has also given scientists new insight into the paths taken by man as he journeyed across the Earth (Nature online, February 7, 2007).
More than half of all human beings are infected with Helicobacter pylori, a bacterium that can cause stomach ulcers. Like humans, the bacteria are also split up into numerous regional populations. A team of scientists led by Mark Achtman at the Max Planck Institute for Infection Biology, François Balloux at the University of Cambridge and Sebastian Suerbaum at Hanover Medical University have found signs of the parallel evolution of man and H. pylori. Using mathematical simulations, the researchers demonstrated that H. pylori must have left East Africa at the same time as man - around 60,000 years ago. This astonishing conformity was uncovered by scientists when they compared the nucleotide sequencing patterns in the DNA of human and H. pylori populations.

In order to characterise the individual populations, the scientists employed the principle of isolation by distance. According to this principle, the genetic distance between two populations has a linear correlation with the length of the migration paths taken since they were separated. "It's actually quite logical," explains Dr. Mark Achtman, "because in the time that elapses after a population leaves its point of origin, the number of mutations in its genetic makeup continually increases."

However, while man was spreading throughout the world, human populations had to repeatedly pass through what scientists call genetic bottlenecks: when a population shrinks, the gene pool also becomes smaller. These losses in genetic diversity linger, even when the population starts once again to increase in number. Since the Homo sapiens populations usually had to pass through several genetic bottlenecks on their way across the globe, their genetic diversity declined the further they journeyed from their origin in East Africa.

Scientists have now uncovered similar signs of historical population migration in the genetic makeup of H. pylori. However, the genetic diversity of the bacteria is larger than that of man. This paves the way for researchers to use H. pylori data to work out the migratory movements of modern man. "The parallels between the spread of man and of H. pylori are truly astonishing," says Achtman. "This bacterium could help us attain further information on aspects of human history that are still hotly disputed today if we analyzed H. pylori in conjunction with human data." For example, after leaving East Africa, the H. pylori population spread through limited localities in southern Africa, West Africa, Northeast Africa, India and East Asia. The genes of bacteria isolated in Europe, for instance, reveal influences from Central Asia - an indication that human immigrants came to Europe from Asia.

Original work:

Bodo Linz, Francois Balloux, Yoshan Moodley, Andrea Manica, Hua Liu, Philippe Roumagnac, Daniel Falush, Christiana Stamer, Franck Prugnolle, Schalk W. van der Merwe, Yoshio Yamaoka, David Y. Graham, Emilio Perez-Trallero, Torkel Wadstrom, Sebastian Suerbaum, Mark Achtman

An African origin for the intimate association between humans and Helicobacter pylori

Nature online, February 7, 2007

Adapted from materials provided by Max-Planck-Gesellschaft.