genetic evidence alone is not enough to reconstruct the timing and spread of short-term plague pandemics, which has implications for future research related to past pandemics and the progression of ongoing outbreaks such as COVID-1

The team studied genomes from strains with a worldwide distribution and of different ages and determined that Y. pestis has an unstable molecular clock. This makes it particularly difficult to measure the rate at which mutations accumulate in its genome over time, which are then used to calculate dates of emergence. Because Y. pestis evolves at a very slow pace, it is almost impossible to determine exactly where it originated.

These changes from the Y. pseudotuberculosis progenitor included loss of insecticidal activity, increased resistance to antibacterial factors in the flea midgut, and extending Yersinia biofilm-forming ability to the flea host environment.

the interactions of Y. pestis with its flea vector that lead to colonization and successful transmission are the result of a recent evolutionary adaptation that required relatively few genetic changes.

The Yersinia–flea interactions that enable plague transmission cycles have had profound historical consequences as manifested by human plague pandemics. The arthropod-borne transmission route was a radical ecologic change

Alternative putative etiologies of the Black Death include a viral hemorrhagic fever [16] or a currently unknown pathogen [19]. In part, these alternative etiologies reflect apparent discrepancies between historical observations of extremely rapid spread of mortality during the Black Death with the dogma based on Indian epidemiology that plague is associated with transmission from infected rats via blocked fleas

However, the Y. pestis genotype identified in our skeletons from Bergen op Zoom differed from those found in Hereford and Saint-Laurent-de-la-Cabrerisse, implying that Bergen op Zoom (and possibly other parts of the southern Netherlands) was not directly infected from England or France in AD 1349.

Our finding of identical genotypes (based on 20 markers) in Saint-Laurent-de-la-Cabrerisse and Hereford thus lends support to historical evidence [2,25] which suggest that plague spread from France to England (Fig. 1) in the second half of the 14th century.

our aDNA results identified two previously unknown but related clades of Y. pestis associated with distinct medieval mass graves. These findings suggest that plague was imported to Europe on two or more occasions, each following a distinct route.

Here we identified DNA and protein signatures specific for Y. pestis in human skeletons from mass graves in northern, central and southern Europe that were associated archaeologically with the Black Death and subsequent resurgences. We confirm that Y. pestis caused the Black Death and later epidemics on the entire European continent over the course of four centuries.

Figure 1 The spread of the Black Death in northern Europe, 1346–1351.

The following year the Black Death had the entire country in its grip according to contemporary chronicles, annals, and anniversary of deaths registers.

Rats and fleas and thus the contagion itself could also be spread by transport going in the opposite direction, carrying residues of grain and grain-based provisions that would feed the carriers of the disease on their journey.

trade in heavy goods like timber, cloth, artefacts in limestone and lead, and not least grain over long distances rapidly gained impetus from the middle of the 12th century.

It progressed up through the Bristol Channel to Bristol before advancing along the Severn to Gloucester.

it struck Norway on two fronts: in Oslo, by then the largest town in the southern part of the country,40 and Bergen on the west coast.41 From these two points the infection spread inland along main roads and pilgrim routes, both south of the Oslo fjord and all the way up north to the Archdiocese of Nidaros, where the archbishop himself succumbed in 1349.42From Norway the plague must have been transmitted to Denmark, where, in the autumn of 1349, it erupted in the port of Halmstad

From Grimsby and Hull, both situated at the entrance to the Humber, the epidemic advanced inland along the rivers of Trent and Ouse until it eventually reached the cathedral city of York in May 1349.

the Black Death arrived in Dalkey and Drogheda, two small towns situated in the English colony known as the Pale on the east coast of Ireland, in August 1348.

the infection spread along the Thames from east to west to reach London towards the end of 1348.

he Black Death spread from France in the summer of 1348 to the port of Weymouth on the southern coast of England

The rat flea, Xenopsylla cheopis, admittedly had the most favourable conditions to do so, but research demonstrates that it was extremely sensitive to changes in temperature and humidity

However, there is no evidence to suggest that rats were involved in the spread of the plague in the Middle Ages. No contemporary historical accounts exist of dead rats being found ahead of an outbreak of the plague

It is possible that the human flea Pulex irritans played a role

the hypothesis that the plague was bubonic in origin and spread along the trade routes of Europe, carried like metastases by the black rat and its parasitic fleas.

The purpose of the present research is to examine various theories concerning the origin of the Black Death, to record its routes of dissemination in the Nordic countries and across the British Isles, and to compare the pattern of that dissemination with trade routes carrying grain throughout northern Europe

Note also that testators left cloth as bequests during the epidemic. Apparently they were not as concerned with clothes retaining miasma as were anti-plague ordinances of the government.

The ship of Jaume Ferrer departed for the River of Gold on the 10th of August of 1346, the feast of St. Lawrence.