Researchers from the University of Oslo in Norway are examining remnants of bacterial DNA from the Black Death in the teeth of its victims as part of an effort to understand the evolution and ecology of the plague. Other members of the team are investigating rodent immunity and the impact of climate.
Although plague is commonly associated with the Middle Ages, there are 2,000 cases of the disease worldwide every year. Although most of these occur in Madagascar and Congo, plague is also reported in the deserts of North America and a large belt of Central Asia.
So far, there have been three major plague outbreaks in the last 2,000 years. The first occurred at the end of the Iron Age and lasted for 200 years. This outbreak was followed by the Black Death, a pandemic lasting for around 400 years. The third, however, began in China at the end of the 19th century and is considered to be ongoing.
A man died from plague last year in Yumen, Northern China, leading to 30,000 inhabitants of the city being held in isolation. A further outbreak occurred in Madagascar in November.
“The transitions between the three plague outbreaks are not completely clear,” says Prof. Kjetill S. Jakobsen. “There was also an overlap between the second and the third outbreaks. Plague can completely vanish for decades, and then return.”
The work of researchers at the Centre for Ecological and Evolutionary Synthesis (CEES) at the University of Oslo in Norway could help to predict the next major plague epidemic.
Modern molecular methods of research have allowed for scientists to expand their knowledge of the three plague pandemics. By analyzing the DNA of plague bacteria from the first two pandemics, researchers are charting their evolutionary development.
At present, Barbara Bramati of CEES is looking for answers within the teeth of 2,700 plague victims from Europe and Asia. Plague bacteria often entered the bloodstreams of victims and hence can found within their dental pulp.
“The DNA remnants are often fragmented and destroyed,” she states. “This makes reconstructing the genetic material an arduous task.”
Making the process easier will be the opening of a new DNA laboratory at the university – a facility that will be the largest of its kind in Europe.
As well as examining the genome of the plague, researchers from CEES are investigating factors that enable the disease to spread.
Some rodents have demonstrated a remarkable tolerance to plague bacteria, and rats have been identified as spreading the disease in the past. However, while there is no proof that they have carried the disease, gerbils appear to be even more successful at tolerating it.
“Sometimes a single bacterium kills a mouse,” says Pernille Nilsson. “Common rats can tolerate injection of 10,000 bacteria. Gerbils can tolerate 100 billion bacteria. That is 10 million times as many bacteria.”
Researchers in China identified this high level of tolerance by injecting the rodents with plague bacteria until half of their number died.
Nilsson is now investigating the gerbil genome to find an explanation for the high level of contagion tolerance. In order to do this, the team need to compare the DNA of surviving gerbils with the fully sequenced gerbil genome.
“We must find the regions in the genome where there is natural variation among individuals and the regions of the genome that show specific differences between the gerbils that survive and the ones that die. We have not identified these regions in the genome yet,” she explains.
Sequencing the genome is a time-consuming process. The gerbil genome consists of 2.4 billion base pairs and in the process of sequencing, only 100 base pairs can be read at one time. Pairs need to be processed multiple times in order to accurately locate small nucleotides in the genome.
In addition, comparing one gerbil genome to the fully-sequenced gerbil genome requires a week of access to a supercomputer.
At present, the researchers believe protection from the disease stems from a hereditary congenital immune system.
Alongside these efforts, Boris Schmid is analyzing associations between climate variations, plague outbreaks and concurrent rodent populations. “This data will give us an idea as to how plague and the climate are linked, and is important for us to be able to predict the next plague outbreak,” says Schmid.
“It is tempting to speculate whether the ecology of the locations in which the pandemics started played a role in their level of destruction. We can understand the serious pandemics in the past, present and future by looking at the link between climate conditions and plague dynamics,” concludes Prof. Nils Christian Stenseth, Chair of CEES.
Recently, Medical News Today reported on a microbiological study of the New York subway system that found traces of anthrax and bubonic plague present. These DNA traces were identified at very low levels, with no indication that the microbes were alive.