Field of Science

History of Bacteriology: Miasmas and Contagions

Have you ever found yourself walking down a street, and be confronted with a pungent turd blocking your path?
You don't know where it came from, but whether it be a dog or a tramp, you know to avoid it. It's a natural instinct. Toiletry behaviour can be found all over the natural world. Even tree sloths will make the effort to climb down to defecate far away from where they feed. The disgusting odours we associate with putrefying meat, faeces and death are ones we naturally try to avoid, and when that isn't possible we try to cleanse ourselves thoroughly so that we don't have to experience their stench.
If you were to ask me where the Miasma theory came from, I would point not to any one individual, but to that instinct of disgust. It was it's link to this natural response that also made it so difficult for people to dismiss miasmas even when confronted with overwhelming evidence that they didn't exist.
Many peoples across the world developed their own culture of hygiene and cleanliness, which usually involved some form of cleaning ritual and disposal of waste.
Often, these traditions would propose a specific association between bad smells and disgusting objects with disease. Across the world, incense and pungent smelling products tended to be used for treatments. Getting rid of the smell equated to getting rid of the disease.
Hippocrates advised people to stay away from places with "bad air" in many of his writings, and expounded the earliest iteration of the Miasma theory. His work was translated into multiple languages and passed through the ancient world, forming the basis of medical practice for centuries after his death. The concept of "Bad air" being the cause of diseases became well established. But it was not the only theory of disease people used.
In 1546, Girolamo Fracastoro published "De Contagione et Contagiosis Morbis", where he wrote about the "Contagion" theory of disease. He drew together various observations on disease that he had accumulated over his forty year long career as a physician. He proposed that diseases could be caused by the transfer of some imperceptible, yet corrupt matter between the sick and the well.  He called this corrupt matter "the seeds of contagion". He proposed that these seeds could spread in three distinct ways. Through direct contact with infected people, through contact with inanimate objects that had been in contact with sick people (he named these "Fomites") and at a distance. He connected these seeds to "putrefaction", in that they could cause it in their hosts, explaining diseases such as gangrene. His explanations generally attempted to reconcile contagion with Hippocratic theories that all diseases were caused by imbalances between four mysterious "humours" found within the body. The types of disease would be determined by which particular humour interacted with specific seeds.
His work sparked off as debate throughout Europe. Whilst the idea of contagion became more widely known, there was much debate over its theoretical causes and his interpretation of the work of Galen and Aristotle and objection over creating a whole new form of life, these seeds, out of thin air.  Fracastoro's most fierce critic was one of the first converts to contagion, Giambattista da Monte. The two would continually clash over the differences in their ideas, a hostile relationship that would eventually develop into one of mutual respect. The students who were privy to these lectures came from all over Europe, and when they returned to their home countries, they would bring the theory of contagion with them.
When proponents of "Bad Air" theory heard of the contagion theory, sparks most conspicuously did not fly. There were arguments, but they were no less vicious than the ones going on between the people who accepted contagion as a theory. Contagion theory still accepted that diseases could be caused by "Bad Air", but that the reason for this was that the air was filled with the "seeds of disease". "Bad Air" Theory held that sufferers of disease were primary sources of "Bad air", and people could catch disease from close contact with the sick.
However, the "Bad Air" theory got a boost in the 17th century when the Hippocratic corpus began to be re-evaluated by a number physicians. I've already talked about a gentleman named Thomas Sydenham who was key for bringing the Hippocratic corpus into the English language and kick starting a new era in evidence based medicine. He lived in an era where doctors applied many treatments based on theoretical ideas, such as bloodletting, sweating and forcing patients to vomit in order to "balance the humors". Sydenham however recognised that many of these treatments did more harm than good, and that the only way to truly divine a theory of medicine would be by a patients bedside.
Unfortunately, he did not have access to the fabulous microscopes of Anton Leeuwenhoek (No-one did, Leeuwenhoek was incredibly protective of his work) so he had no way of determining an evidence basis for contagion. In the end, he tended to favour Hippocratic theories of "Bad air" being the cause of disease, as he had no evidence available to prove otherwise.
In a treatise about malaria* written by Giovanni Maria Lancisi called "On the Noxious Effluvium of Marshes"he connected the disease with the noxious smells emanating from marshes and the mosquitoes that live within them. He gave a name to these noxious smells, he was the first to call them "Miasmas".
The Contagion theory and the Miasma theory were no longer seen as compatible by a growing number of physicians.
His writings went global, and were of particular influence in the United States on medical professionals such as Noah Webster and Benjamin Rush. During an outbreak of Yellow Fever in Philadelphia, many suspected that it had arrived from a contaminated consignment of Coffee from a ship with a crew riddled with the disease. However, Benjamin Rush disagreed with this vehemently, suspecting it had come from the marshy miasma's he believed surrounded the city. Even though Rush believed that contagion played a role in these early cases, that belief eventually waned. By 1799 he actively protested against quarantine procedures for sailors entering the city. By 1805 he began writing treatises to dismiss the idea of contagionism.
Maritime Quarantine procedures were a problem the world over, and cut into the business of many growing companies. It was in the interests of these companies to fuel the backlash against Contagionism.
When quarantine procedures** failed to prevent the Liverpool Cholera epidemic, a major blow was struck to the theory. The Cholera Riots demonstrated the true chaos which could follow a disease epidemic, and spurred people to enact new precautions against these outbreaks. These precautions would be based on the theory of Miasma.
Edwin Chadwick was a major supporter of the Miasma theory, and a vehement anti-contagionist. . He was aware that often, Cholera was associated with unsanitary conditions, and he realised that if the Miasma theory was true, then the greatest threat to peoples health was the presence of open sewers within cities. Through his efforts, open sewers were eliminated, and the cleaning of the streets began to be seen as an issue of public health. These massive clean-up efforts were incredibly effective, and would fuel further support for Miasma theory.
As we now know, Miasma's do not exist, at least not in the form that most people believed in at the time. There are solid reason why humans developed an aversion to particular bad smells. Often the sources of these smells would contain harmful diseases. Clearing out sewage from cities helped people because it meant that flies that fed on faeces could not then transfer microbes from those faeces onto food. It removed opportunities for bacteria such as typhoid from spreading through the streets in shit.
Whilst Chadwick's reforms produced results, they still had problems that are a lot more obvious to modern readers. Whilst the sewers were covered, they still discharged into the water supply, which caused regular outbreaks of cholera and typhus within the city.
Nevertheless, the Miasma Theory had risen to prominence by the 1830's, and its supporters would often define themselves as "anti-contagionist".
But the picture, as always, is more complex. Contagionism, whilst under attack, was far from dead.

*The very name "Malaria" refers to the bad air theory, with "Mal" meaning bad and "Aria" referring to the air. Although it didn't necessarily just refer to our modern interpretation of the disease. Many sweating sicknesses similar to what we understand as malaria would be referred to by its name as well.
** No-one knew of the waterborne nature of the disease, and nor was it thought that fomites could have played a role.


Curtis V.A. (2007). Dirt, disgust and disease: a natural history of hygiene, Journal of Epidemiology & Community Health, 61 (8) 660-664. DOI:

Nutton V. (1990). The Reception of Fracastoro's Theory of Contagion: The Seed That Fell among Thorns?, Osiris, 6 (1) 196. DOI:

Ayliffe G.A.J, English M.P. (2003) Hospital Infection: From Miasmas to MRSA, Cambridge University Press. Link

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