Yersinia pestis, Ghost of Plagues Past

Skeleton Blog2

Who’s afraid of the big bad plague? Bet you the owners of the bones above were. This Halloween, we’re highlighting the work of researchers who tested (extremely carefully) for the presence of the pathogen Yersinia (Y.) pestis (a.k.a., the “Bubonic Plague”) in human skeletal remains from three sites in Germany and Switzerland.  Thought to be victims of the Black Death, these individuals died alongside an estimated 75-200 million other Europeans affected by this outbreak of the plague, which diminished Europe’s population during the 14th century by one third.

The specialized protocol the researchers used in this study was carefully created to be in line with modern plague diagnostic procedures and to address the unique challenge of working with ancient DNA (aDNA), which varies in quality from sample to sample and is easily contaminated with modern DNA. Contamination is common and can be hard to identify, often resulting from poor handling practices at excavation or during preparatory procedures. The researchers  did their best to avoid the possibility by thoroughly cleaning the surfaces of the bones and teeth that samples were drawn from, and using multiple controls to highlight any points of contamination from the laboratory that occurred during the experiments. At a time when the results from testing of aDNA samples can be highly contested, a validated  DNA replication process was used to ensure authenticity of the tests and to prevent misinterpretation of the results by the scientific community.

Bones and teeth from 29 individuals, ranging from 300-600 years old, were collected from sites in Manching-Pichl and Brandenburg in Germany and Basel, Switzerland and housed at the State Collection for Anthropology and Palaeoanatomy  in Munich. Selected samples were then moved to newly constructed labs at the ArcheoBio Center of the Ludwig Maximilian University  Munich for preparation and aDNA extraction. Researchers followed a strict protocol to prevent any sample contamination at this stage. The new facility contains three air-locked and pressurized rooms, each meant to provide a contamination-free workplace for processing aDNA samples for replication. Before admittance to the three-room complex, staff were required to shower, wash their hair, and enter a gowning room to replace their freshly laundered clothes with two pairs of gloves, a hairnet, hooded overalls, and a screened facemask. A second gowning room required the addition of another set of hooded overalls. Scientists then moved through the rooms sequentially, preparing the aDNA samples and negative controls (meant to test for contamination in the replication process) for analysis.

Once preparatory procedures were complete, sealed tubes containing the negative controls and aDNA were transferred to the Bundeswehr Institute of Microbiology for the addition of positive controls (tubes containing DNA from Y. pestis), DNA replication and analysis. Of the 29 samples tested, seven contained fragments of a Y. pestis gene after an initial round of replication, and four additional samples tested positive for Y. pestis after further rounds of testing.

Although the skeletons above are not, Y. pestis is still alive and well in parts of the world. Now called the “Modern Plague” to differentiate it from previous plagues caused by the same pathogen, such as Justinian’s plague and the Black Death, the disease affects 1,000-3,000 people per year. Modern treatments have thankfully limited the number of deaths that result from these cases, leaving us less likely to end up in the ground after getting sick, like these poor individuals. Nevertheless, research on the presence of the pathogen in ancient samples remains crucial for our continued understanding of how this disease affected our population in the past.

So, in case you need a scary costume idea for tonight’s festivities, why not draw some inspiration from our friends above? A skeletal Black Death victim and a masked, double-overalled plague researcher sound like great costume ideas to us.

Happy Halloween from PLOS ONE!

Citation: Seifert L, Harbeck M, Thomas A, Hoke N, Zöller L, et al. (2013) Strategy for Sensitive and Specific Detection of Yersinia pestis in Skeletons of the Black Death Pandemic. PLoS ONE 8(9): e75742. doi:10.1371/journal.pone.0075742

Image Credit: Courtesy of the authors and the Bavarian State Department of Historical Monuments

Lions Like to Cuddle Too


Who doesn’t love a good cuddle? A study published today in PLOS ONE demonstrates that lions are no different than us when it comes to snuggling, though they’re not only in it for the warm fuzzies. Researchers studying captive lions at the Tama Zoological Park, Tokyo, found that affectionate behavior between individual lions helps foster bonds and strengthens the pride as a whole.

Physical exchanges were common throughout the observed group of lions, though the males and females seemed to prefer different methods for showing their affection. While about 97% of observed licking occurred between lionesses, male lions in the zoo seemed to prefer the head rub, and directed a serious portion of their head-rubbing efforts towards other males. Females also used the head rub, but mainly in interactions with males in the group and less frequently with other females. Almost all behaviors were reciprocated, especially between males and females.


Researchers investigated why these behaviors differed from the affiliative behaviors seen in other animals, as well as the reasons for the apparent discrepancy between male and female behaviors. They postulate that shared group odors may explain why lions specifically choose to rub heads instead of any other behavior —the spotted hyena, for instance, exposes its genitals upon greeting members of the group. The lionesses licking each other could be an extension of their maternal behavior and instincts normally shown towards their cubs. More research, particularly on the behavior of lions in the wild, is needed before we can say for sure.

While we don’t have any final answers on affectionate behavior between captive lions, this research reveals how these behaviors affect this pride’s group dynamics. In the wild, coalitions of male lions compete for the right to live among, and mate with, the lionesses of an established pride. Once a group of males has settled itself in a pride, they must be on the offensive at all times to ward off attacks from gangs of nomadic male lions. Understandably, greater numbers means greater power and a better chance of standing strong against outside invaders. So, how does a group of unruly male lions keep its numbers high? Head-rubbing seems to be at least part of the equation.

Citation: Matoba T, Kutsukake N, Hasegawa T (2013) Head Rubbing and Licking Reinforce Social Bonds in a Group of Captive African Lions, Panthera leo. PLoS ONE 8(9): e73044. doi:10.1371/journal.pone.0073044

Image:  Image from Figure 1 of the manuscript