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Natural history of plague © schousboe

The Natural History of Plague

Recent studies of aDNA have yielded new and important information concerning the natural and clinical history of plague. A new comprehensive review offers an up-to-date history

The plague is caused by a zoonotic bacterium, Yersinia pestis. First isolated in 1894, it was identified as the cause of the Hong Kong Epidemic. Later, in the 20th century, the same bacterium was shown to have caused the Black Death. Recently – due to studies of the aDNA – the same bacterium has been shown to have caused the Justinian plague as well as very recently epidemic events in prehistory 2800 BC. Also – which the article does not refer to – the discovery of the likely role of a plague epidemic following in the footsteps of the Yamnaia.

During its natural history, the pathogen has undergone numerous mutations at different rates, transforming it from a variant of Yersinia pseudotuberculosis to more or less virulent Yersinia Pestis, traditionally divided into three bio-variations termed the Antiqua, the Medievalis, and the Orientalis – named after three major epidemics, the Justinian Plague, The Black Death, and the Hong Kong epidemic. The three variants may still be found in reservoirs in respectively Central Asia, Siberia and Russia (the Antiqua), Central Asia (the Black Death), and China (Orientalis). However, the biotypes intermingled – also historically. To this should be added the knowledge, that the bacterium mutated while the different waves of an epidemic played out.


Transmission to humans from carriers typically happens via flea bites, but it can also follow through direct contact with infected animals for instance by handling or eating them, or by inhaling aerosols from patients. Modern incidents tell of infections from squirrels, but also via predators infected from carcasses (Pumas in Yellowstone). Plague comes in three forms – bubonic, septicemic and pneumonic. While people can survive bubonic plague, the septicemic and pneumonic forms are 90-100% deadly.

Yersinia Pestis is a highly virulent pathogen known to infect over 200 different mammals. Of these, more than 351 species of rodents can act as hosts, and 279 have been identified as plague carriers. Thus, the former focus among historians on the rat as the main vector would seem to be excessive. Marmots may have played a significant role in the northern parts of Europe, causing the epidemics known as the Sylvatic or (wild) plagues spreading among groundhogs, great gerbils, squirrels, prairie dogs, rabbits, and water voles. Although human contact may at first sight be expected to be rare, hunters and trappers in Siberia and further west into Scandinavia, would historically be daily exposed, thus explaining the heavy toll that the Black Death also had in secluded spots in Norway and Sweden (as well as during the Justinian plague in Bavaria). Today, the so-called wet markets in China and Asia are not just potential petri dishes for viruses like Covid but also plagues.

As opposed to the Sylvatic plagues, the Urban form is epidemic and relies on rats as the hosts and fleas as the vectors. However, the epidemic character of the urban plague has also to do with the fact that written documentation describes them as such. As opposed to this, the sylvatic form is only known from archaeology and paleo-genomics, leading to a more confused impression, such as the puzzlement forged by the pattern of infections and mortality in Norway (with no particular black rat population in the interior, see Benedictow).

Exactly how lethal the different plagues hit, has been debated. Currently, though, the opinion is that the plagues hit hard, albeit at different levels in different regions and types of settled areas, ranging – during the Black Death – between 30 – 50% with averages of 45%. The recurrent infections also raise questions which need to be addressed in the future. As is known, the Black Death was not just a one-off epidemic hitting Europe harshly between 1348-51. For at least 350 years, outbreaks continued. Were they sourced in natural reservoirs? Or did they take place due to the constant mutations of the bacterium and its ability to bypass the developing immune system of people?

One particular element to be considered in the future (and which the review does not consider) will be the interplay between climate deterioration and the four great plagues. The plague victims discovered in graves from 3000-2800 BC, played out during the so-called neolithic decline when a unique combination of solar activity, cosmic rays and decentering of the geomagnetic fields. This might be compared to the chronological correspondence between the volcanic-forced LALIA AD 536-41 and the Justinian plague. Finally, the climate downturn took off in the later Middle Ages ultimately leading to the Little Ice Age. The mechanism appears to be the increase in the number of rodents caused by warm and wet conditions. Followed by less favourable climatic conditions, these rodent populations collapse, forcing the fleas to migrate to other mammals; that is people.


The Natural and Clinical History of Plague: From the Ancient
Pandemics to Modern Insights
Antoni Bennasar-Figueras
In: Microorganisms, January 2024. Open Source

Antoni bennasar-Figueras is professor in Biology at Universitat de les Illes Balear


Emergence and Spread of Basal Lineages of Yersina pestis during the Neolithic Decline
By Nicolas Rascovan, Karl-Goöran Sjögren, Kristian Kristiansen, Rasmus Nielsen, Eske Willerslev, Christelle Desnues, Simon Rasmussen
In: Cell 2019, vol 176, pp 295 – 305

Golden Torques © Medieval Histories

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Tournament. © Jenna Goodwin 71183546 Dreamstime

Which warhorse would you shop for if you were a Medieval knight?

Which horse would you prefer if you were a Medieval knight? A Jaguar, Volvo or Mercedes?

If your car was a horse, which one would you prefer to ride if you belonged to the Medieval elite? And why? This question is answered by a new archaeological analysis of an animal cemetery in London discovered thirty years ago. Not a locally produced, it appears. Newly published results from an archaeological analysis show how late medieval and Tudor elites imported superior animals to the UK for jousting and as status symbols.

Using advanced archaeological science techniques, including studying chemical composition, researchers have been able to identify the likely origins of several physically elite horses and the routes they took to reach British shores during the formative years of their life.

These animals – akin to modern supercars – were sourced from a variety of locations across Europe specifically for their height and strength and imported for use in jousting tournaments and as status symbols of 14th- to 16th-century life. They include three of the tallest animals known from late medieval England, standing up to 1.6 metres or 15.3 hands high, which while quite small by modern standards would have been very impressive for their day.

The skeletons of the horses were recovered from a site under the modern-day Elverton Street in the City of Westminster, which was excavated in advance of building works in the 1990s. In medieval times, the cemetery would have been located outside the walled City of London but was close to the royal palace complex at Westminster.
The research, led by the University of Exeter, and funded by the Arts and Humanities Research Council, is published in the latest edition of Science Advances.

“The chemical signatures we measured in the horse’s teeth are highly distinctive and very different to anything we would expect to see in a horse that grew up in the UK,” said Dr Alex Pryor, Senior Lecturer in Archaeology and lead researcher. “These results provide direct and unprecedented evidence for a variety of horse movement and trading practices in the Middle Ages. Representatives for the King and other medieval London elites were scouring horse trading markets across Europe seeking out the best quality horses they could find and bringing them to London. It’s quite possible that the horses were ridden in the jousting contests we know were held in Westminster, close to where the horses were buried.”

Strontium Analysis

Curb bit from the beginning of the 16th century, France. © The Metropolitan Museum. Open Domain
Curb bit from the beginning of the 16th century, France. © The Metropolitan Museum. Open Domain

In the first experiment of its kind to be conducted on medieval horse remains, the researchers took 22 molar teeth from 15 individual animals and drilled out portions of the enamel for isotope analysis. By measuring isotope ratios of the elements strontium, oxygen and carbon present within the teeth and comparing the results with known ranges in different geographies, the team was able to identify the potential origin of each horse — and accurately rule out others, including prime European horse-breeding centres such as Spain and southern Italy.

The scientists writes that at least half of the horses had diverse international origins, possibly Scandinavia, the Alps and other northern and eastern European locations. The results, the researchers conclude, were consistent with the breeding patterns of royal stud farms, where horses would reside until their second or third year, before they would either be broken and trained or sent elsewhere to be sold.

Physical analysis of the teeth revealed wear suggestive of heavy use of a curb bit, often employed with elite animals, especially those groomed for war and tournaments after the 14th century. Bit wear on two of the mares also suggested they were used under saddle or in harness and for breeding. And analysis of the skeletons revealed many of them to be well above average size, with several instances of fused lower thoracic and lumbar vertebrae indicative of a life of riding and hard work.

“The finest medieval horses were like modern supercars — inordinately expensive and finely tuned vehicles that proclaimed their owner’s status,” added Professor Oliver Creighton, a medieval specialist at the University of Exeter and part of the research team. “And at Elverton Street, our research team seem to have found evidence for horses used in jousting – the sport of kings, in which riders showcased their fighting skills and horsemanship on elite mounts.

“The new findings provide a tangible archaeological signature of this trade, emphasising its international scale. It is apparent that the medieval London elite were explicitly targeting the highest quality horses they could find at a European scale.”

Horses from Esrum in Denmark?

Christian David Gebauer: Drawing of a "Frederiksborger" 1805. The horse is depicted in the grassland next to the royal forest. The Castle may be seen in the back. Source: Wikipedia
Christian David Gebauer: Drawing of a “Frederiksborger” 1805. The horse is depicted in the grassland next to the royal forest. The Castle may be seen in the back. Source: Wikipedia

Some of the horses excavated in London may have come from the famous stud farm at Esrum in Northern Zeeland in Denmark. 

In the Middle Ages, Esrum was famous for its horses, bred on a mixture of Frisian horses and imported horses from Andalusia providing a combination of muscle and speed. This stud farm was a major income for the Cistercians at Esrum, who achieved special permission in 1184 to breed and sell their horses if the income was sent to Citeux in France, from where it was redistributed to newer and less wealthy monasteries. After the Reformation, the King took over Esrum Monastery and its stud and moved it to Frederiksborg. Here, the ancient breeding of the “Frederiksborger” is still carried out. We know, the export of horses played a large role in the Danish economy in the Middle Ages. 

If some of the horses in London were Danish, they might have arrived as gifts from the Danish King, Erik of Pommerania, who was married to an English Princess, Phillipa in 1405. Part of her trusseaux consisted of two wagons and eight equestrian harnesses and saddles, but no horses. Apparently, even if she had a favourite pony, she might be expected to be provided for properly at her arrival in Denmark. Why bring candy to the chocolate factory?


Tournament. © Jenna Goodwin 71183546 Dreamstime


Press release from University of Exeter: Original written by Andrew Merrington.


Isotopic biographies reveal horse rearing and trading networks in medieval London.
By Alexander J. E. Pryor, Carly Ameen, Robert Liddiard, Gary Baker, Katherine S. Kanne, J. Andy Milton, Christopher D. Standish, Bastian Hambach, Ludovic Orlando, Lorelei Chauvey, Stephanie Schiavinato, Laure Calvière-Tonasso, Gaetan Tressières, Stefanie Wagner, John Southon, Beth Shapiro, Alan Pipe, Oliver H. Creighton, Alan K. Outram.
In: Science Advances, 2024; 10 (12) DOI: 10.1126/sciadv.adj5782


The Medieval Warhorse Cover

Horse trade in tudor cover

The Medieval Warhorse