Bubonic Plague – Lice – Hosts for The Black Death Bug. One important question facing the World Health Authorities is ‘Where will the next global pandemic come from?’ Horrific bugs like Ebola, SARS and Pandemic strains of Flu live innocuously in other animals for long periods before mutating and then killing thousands or even millions of humans. Recent research into the Plague bacterium indicated it has accompanied human communities for 5000 years and has hidden between epidemics very close to home – this is where the human lice research gets interesting.
Regular visitors to ChrisDuggleby.com will remember my recent article about a German invention that uses a gas plasma in a hair brush to kill head lice without harming the poor human ‘victim’ (the link to that article is here). This little device is probably going to be a big success in the market place because it annihilates the little blood suckers in an environmentally friendly way. As lice are becoming immune to other medications such a non chemical solution to this irritating problem may be essential.
After you have read my description (below) of some other recent research I am sure you will agree that this high-tech grooming device could become an essential tool in our armoury against killer epidemics. There have been three recent pieces of research into the plague bacterium Yersinia pestis which turn some long held beliefs about this bug on their head.
The first piece of research showed that the plague bacterium has been accompanying human civilisation since the bronze age – at least 4500 years. Prior to this we knew from written records that plague had terrorised societies since 542 AD when it was estimated to have taken the lives of 40% of the population of Constantinople. This was the first recording of what is now known as bubonic plague in which buboes or large swellings of the lymph nodes occur.
This was the beginning of what is referred to as the first plague pandemic which continued to spread in waves across the world for the next 200 years. It is estimated to have killed 100 million people and reduced the population of Europe by 50% by the year 700. The second pandemic occurred between the 14th and 19th centuries and is also estimated to have reduced the world’s population by approximately 100 million. This second pandemic reduced the population of China by a half, the population of Europe by one third of the population of Africa by one eighth.
During this period the plague swept across the populated world and was given the name Black Death. This was because the skin of affected parts of the body turned black when it died (referred to as necrosis) as in the pictures below:
The third pandemic of bubonic plague took place in the 19th and 20th centuries. It started in China and spread to all inhabited continents of the world. It killed 12 million people in India and China. Major ports were severely affected – during an epidemic in Hong Kong death rates of 90% were identified. It reached the US in 1900 leading to the San Francisco plague from 1900-1904. It was not eradicated in the US until 1959.
Although these three pandemics have been well documented the research referred to above confirmed that the plague has been with us much longer. This work, by Eske Willerslev from the University of Copenhagen (published in Cell) took DNA from the teeth of Bronze age skeletons (approximately 4500 year old) and identified that it also contained DNA from the the plague bacteria Yersinia pestis. In particular these scientists identified two specific areas of Yersinia pestis DNA that confirmed it was the virulent strain that also caused the bubonic plague of later pandemics.
One of ‘markers’ in the DNA indicates the bacteria was able to survive in the gut of blood sucking fleas, important transmitters of the disease between mammals. The flea is also a ‘victim’ of the plague bacteria – it invades the flea’s gut and forms a lump there which prevents the flea from digesting its food. The flea gets desperate for nutrition and aggressively pierces the skin of potential hosts looking for food. Due to its sick condition it vomits blood into the wounds and thereby passes on the killer bacteria into a new host – transmitting the plague further. The flea then dies.
During the major epidemics the fleas were transmitted over large distances by a natural host, the rat. Wherever people would go – their rats would go with them – and wherever the rats went – they took their fleas. Rats and other rodents are hosts for Yersinia Pestis and the flea infects itself with the bacteria when it sucks rat blood. As it becomes sick the flea will also turn to sucking blood from humans as it attempts in vain to get nourishment.
The second important piece of Yersinia Pestis DNA identified by the Copenhagen researchers was the piece that allows it to move through different human tissues. This is important because it means the plague can be transmitted rapidly in its pneumonic form – via people’s lungs like influenza or the common cold. This is the highly contagious form of the disease that killed hundreds of millions of people. Once inside the human host this second piece of DNA allows the bug to move through the body leading to the buboes – identified in bubonic plague (Black Death – see the pictures above).
These findings mean that the highly virulent and deadly form of the plague bacteria which killed hundreds of millions of people in the three major pandemic periods has been with us for at least 4500 years. The researchers suggested that during antiquity plague may have been one of the reasons for major movements of populations to new regions of the World (although they sadly took the disease with them spreading plague into previously virgin territory).
Until a few days ago it had generally been assumed that whenever new epidemics appeared in the west the plague bacterium was reintroduced from the far east. It probably came via the Silk Road from China. If this is correct the DNA of the bacteria leading to each new epidemic in the west would differ slightly because they would be derived from a different strain in the Far East (of which there are several). A second piece of recent research provides more clarity about this.
On 13th Jan 2016 Holger Scholz, a molecular biologist and infectious disease researcher at the Bundeswehr (Army) Institute of Microbiology in Munich, Germany published research findings which addressed these assumptions. His team analysed plague bacterial DNA found in the teeth of some very old skeletons in Germany. Some of the skeletons were from a mass grave at St. Leonhard’s Catholic church in Manching-Pichl, southern Germany – radiocarbon dating confirmed they were from the 14th Century. Other remains were from three soldiers buried in Brandenburg, north-eastern Germany during the Thirty Years’ War (1618–1648).
The conclusion of Dr Scholz and his team was that the plague DNA found in these remains was from the same strain of Yersinia pestis. This was despite the deaths occurring in the 14th and 17th centuries and being physically separated by 500 km. Therefore rather then being reintroduced to Europe from the Far East the researchers proposed that the plague bacterium may have been lying dormant in the west in some other host animal between the major epidemics. If plague was regularly reintroduced from Asia the DNA of different ‘Asian’ genetic strains would be expected.
The role of the rat and its fleas was mentioned above – however the plague bacterium is also known to live in other hosts. In fact there has always been a question about how plague epidemics occurred in parts of Europe in which rats were not prevalent. In the middle ages, before the link with rats and their fleas was understood people were convinced that plague was transmitted through human to human contact.
This brings me to the third piece of research. This was communicated to the Centre For Disease Control by Michel Drancourt and his co-workers at the Université de la Méditerranée, Marseilles (link is here). This team looked at the human louse as a possible host for the strain of Yersinia pestis that caused the Black Death epidemics. If the human louse had a role it might explain why there had been examples of human to human plague transmission in which rats were not involved. It might also clarify why plague had struck in parts of world were rats were uncommon like areas in Scandinavia and Russia.
They infected rabbits with the plague bacterium. All the infected animals died within a day. Only 5 minutes after infecting the rabbits with Yersinia pestis 150 ‘plague free’ body lice were allowed to feed on the rabbits for one hour. The bacteria were confirmed in blood samples taken from the lice. After three days one third of the lice infected with plague were still alive. Infected lice were then allowed to feed on uninfected rabbits for one hour per day and those rabbits also died within one day. Uninfected lice fed on these rabbits and also became infected.
The results from the team in Marseilles shows that the plague bacteria that caused Black Death can be transmitted from one mammalian host to another via body lice. In addition some of the lice remain alive and infectious three days after leaving the host. This means even when rats and their fleas are absent plague might be transmitted from human to human through ‘bodily contact’ – by the victims sharing blood sucking lice which pass on the infection. It also shows that infection could occur without bodily contact as long as the lice can feed on their new host within 3 days. This could occur, for example, after a person has died and another person indirectly acquires their lice (from clothes, combs or using their bed – common hereditary items in the middle ages).
It is assumed, based on historical documentation, that in the times when Black Death was prevalent most of the population would have been contaminated with body lice. The authors pointed out that today almost 85% of ‘homeless persons’ have body lice, each having on average 57 lice. They believe that only 10 infected lice would be sufficient to transmit plague to another person. They do not dispute the important role of rats and their flees in historical plague epidemics but they believe their evidence supports the idea that human lice were also important as hosts. Together with the research above it might be suggested that lice acted as a host reservoir for Yersinia pestis in the periods between epidemics.
The reason I have prepared this article is to highlight that our knowledge with regard to where the next major pandemic could come from is far from complete. Some threats like Ebola, SARS, MERS, and Influenza receive a lot of attention. There are however other threats where we think the risk to modern society is relatively low. We do not see many rats in our streets and we feel confident in the ability of our antibiotics to deal with bacterial born diseases like the plague.
However rats are not the only hosts for Yersinia pestis other rodents have been involved as well as cats, monkeys and even mountain lions. The research with body lice highlights the risk from human blood sucking insects. Our weaponry against such potential hosts is gradually being eroded as bacteria develop resistance to multiple antibiotics – in part thanks to use of antibiotics in factory farming (and giving antibiotics to people with viral infections – for which they are useless). Even body lice are becoming resistant to the medications we now commonly use.
Some aspects of the next pandemic are beyond our control but our own inappropriate use of medications could make the situation much worse. The only thing we can predict with certainty is that there will be another pandemic – one day.
If you are interested in reading my other health focused articles try the following