Challenging the Contagion-Only Model of Infectious Disease
The idea that a specific bacterium or virus causes a particular disease — and that this pathogen is the primary determinant of whether a patient lives or dies — has long served as the dominant model for infectious diseases such as smallpox, measles, whooping cough, and scarlet fever
The concept of contagion—the transmission of illness from one person to another — emerged decades before the invention of the microscope, which first made bacteria visible.
Yet, as this essay will explore, a simple equation of “one germ, one disease, one outcome” fails to account for the complex interplay of environment, individual health, and medical intervention that historically shaped whether a patient recovered or perished.
Smallpox and Variolation: Deliberate Infection as a Prophylactic
Building on this belief in contagion, the practice of introducing a “virus” into the skin through “engrafting” was popularized in England around 1717 by Lady Mary Wortley Montagu as a way of combating smallpox.[4]
At the time, the word “virus” derived from the Latin term meaning “toxin” or “poison.”[5] It also referred to the tangible, physical matter (pus or serum) that carried the illness from a sick person to a healthy one.
The modern idea of a specific, unique, invisible particle did not yet exist. The term was purely clinical and descriptive and could also be expressed as “morbid poison” or “contagious fluid.”
“Engrafting” later became known as inoculation — or, more precisely, variolation. It involved transferring material (“virus”) from a smallpox sore into a healthy person, aiming to trigger a mild case that would confer immunity.
The rationale behind deliberately infecting people with smallpox at a time and place of their choosing was that, in a controlled environment and while in optimal health, they would fare better against the disease than if they left infection to chance.
Sydenham, the “Hot Regimen,” and the “Ill Management” of Smallpox
However, the idea that smallpox’s lethality was a simple matter of contagion, with no other factors, has been challenged by a variety of medical men across several centuries. Thomas Sydenham, MD —renowned as the English Hippocrates and regarded as the Father of English medicine — noted in 1688 that “if no mischief be done, either by physician or nurse, [smallpox] is the most slight and safe of all other diseases.”[6]
Sydenham observed that mortality was greater among those who were saturated with expensive sudorifics (sweat-inducing drugs or remedies), kept in hot chambers, and nearly smothered with thick blankets than among the very poor, who, from necessity, were neglected — or rather, left to nature — and who almost always recovered.
He denounced the excessive, misguided care of nurses and friends of the sick, as well as the practice of keeping patients in hot chambers free from fresh air. Instead, he recommended that they drink freely of cold, acidulated fluids (such as lemon juice or vinegar) and enjoy breathing fresh air.
Dr. Cole, a colleague of Sydenham, applied the same principles and thanked Sydenham for his “cure” for smallpox, noting that:
“if Nurses, a sort of People very injurious to the Health of Man, did not obstruct, who by the hot Regimen and Medicines, confound all things, and kill so many before their Time.”[7]
In the early 1700s, Isaac Massey, apothecary at Christ’s Hospital, also observed that smallpox seldom killed unless under “ill management.” He attended to the patients at Christ’s Hospital, which typically housed around 600 children.
Over 20 years, he observed that only five or six deaths were attributed to smallpox. Furthermore, in the preceding eight years, the count stood at a mere solitary fatality.[8]
Nearly a century later, John Birch, a distinguished member of the Royal College of Surgeons, also noted that smallpox was a mild disease and was only:
“rendered malignant by mistakes in nursing, in diet, and in medicine, and by want of cleanliness.”
He observed that for 200 years, “warming and confining the air of the Chamber, and by stimulating and heating cordials,” alone resulted in two-thirds of all smallpox deaths.[9]
In 1864, Dr. Mason Good again observed that treating smallpox with cordials and a hot regimen resulted in it becoming “a severe, and, in many cases, a fatal disease.”[10]
In 1869, Dr. Collins also noted:
“…the mortality was greater amongst those who were saturated with expensive sudorifics, kept in hot chambers, and nearly smothered with thick blankets, than amongst the very poor, who from necessity were neglected, or rather left to nature, and who almost always recovered.”[11]
In 1819, Abraham Rees’s The Cyclopaedia systematically described the hot regimen as a debilitating therapeutic assault that created a vicious cycle of deterioration.
According to Rees, persons suffering from any fever, such as small-pox, measles, or scarlet fever, were typically confined in a “close and heated apartment” without the free circulation of air, and kept under “a load of” bedclothes.
They were given hot drinks and cordials intended to raise the patient’s temperature to the point of “profuse perspiration.” Rees warned that the result was that the skin eruptions were greatly increased, and the symptoms were altered to a “putrid” state in which “the tongue, teeth, and lips become coated with black, clammy, and immovable fur; purple spots appear on the skin; and the whole disease assumes the character of malignancy.”[12]
Other doctors in the late 19th and early 20th centuries recognized the mild nature of smallpox. In 1898, Dr. Montague R. Leverson noted, “…that smallpox is generally a very mild disease…”[13] In 1907, Dr. Smiley stated, “It [smallpox] is a most harmless disease if properly treated. I have treated hundreds of cases without a single fatality.”[14]
Iatrogenic Harm: The Lethal Legacy of Heroic Medicine
During this era, numerous other conventional medical beliefs and practices embraced by medical men had the potential to be lethal. These medical men of the time wielded a range of toxic medications, including calomel (mercury), phosphorus, strychnine, opium, laudanum (opium and alcohol), arsenic, cyanide, chloral, morphine, and jalap (a potent purgative), as essential tools in their medical arsenal.
As one observer noted, Dr. Broady, the author of Medical Practice without Poisons, described the various toxic combinations used by “the dominant school of medicine” of the time. He noted that many of the over 100 medicines were composed of “phosphorus, strychnine, mercury, opium, and arsenic.”[15]
Mercurous compounds emerged as a prevailing choice for medicinal applications and were often considered safe. Among these, calomel, or mercurous chloride, found widespread use.[16] Dr. Beach noted in 1850 that “graveyards conceal the decaying remains of thousands killed by mercury.”[17]
Dr. Dickson noted in 1861 that calomel was “one of the chief agents in man’s destruction!”[18] Russell Thacher Trall, MD, emphatically stated in 1860 that “mercury is a sheet-anchor in fevers; but it is an anchor that moors your patient to the grave.”[19]
In 1727, the Medicina Vindicata stated: “bleeding, vomiting, and purging are the chief operations in physic, by which diseases are cured and health preserved.”[20] In 1747, Charles Perry, MD, noted that copious bleeding was generally practiced for smallpox.
He advised to give medicines through a purge and vomit to “empty the whole alimentary Tube [entire gastrointestinal (GI) tract].”[21] A Treatise on the Small-pox and Measles, published in 1848, noted that the proper treatment for smallpox when symptoms first appear was bloodletting. “If the strength of the patient will allow it, nothing is better in the Small-Pox than to bleed him till he faints…”[22]
Beyond Contagion — Reassessing Smallpox Lethality
Taken together, the observations of numerous physicians over the decades challenge the assumption — common in their own era and still prevalent today — that smallpox was an inexorably lethal disease.
Their collective evidence suggests that the severity of smallpox depended less on the inherent nature of the contagion than on the environment in which patients lived and on how they were managed.
These medical practitioners, writing from the 17th to the early 20th centuries, consistently pointed to the same conclusion: aggressive medical intervention — particularly the “hot regimen” (suffocating confinement and the overuse of heating cordials and sudorifics), bleeding, and toxic medications such as calomel — often worsened outcomes, whereas rest, fresh air, cold fluids, and minimal interference allowed nature to take its course.
In the view of Sydenham, Massey, Birch, and their successors, the disease itself was not the primary killer; rather, it was the “ill management” and “mischief” done by physicians, nurses, and friends that transformed a typically mild illness into a fatal one.
Birch added the observation that errors in diet and sanitation also contributed to smallpox fatalities.
Dr. Oliver Wendell Holmes Sr., the celebrated Harvard physician, voiced a similar condemnation of heroic medicine in the mid-1800s, declaring that “mankind has been drugged to death” by a “colossal system of self-deception” that employed toxic minerals and other abominations instead of addressing the underlying causes of illness.[23]
Dr. Alexander Milton Ross, a Canadian physician, echoed this condemnation in 1888, observing that for decades prior, “millions of human beings … had gone to untimely graves” while suffering under a “medical delusion” that denied fever patients cold water, fresh air, and light.
Instead, physicians prescribed calomel, jalap (a powerful purgative), and bloodletting — depleting patients of their “life blood by the lancet” until they “gave up the ghost.”[24]
Dr. Samuel Dickson of Glasgow offered an even broader indictment in 1855, declaring that “for upwards of twenty-three centuries” — from Hippocrates to the mid-19th century — “to starve, bleed, purge, and torture, had been the all but exclusive business of the man of medicine.”
He observed that this “established practice,” no matter how destructive, went unquestioned by the public so long as the physician possessed a diploma or degree from a reputable institution.[25]
The Limitations of Mortality Statistics
These insights, though marginalized by the rising tide of contagionist orthodoxy and later germ theory, foreshadow modern principles of supportive care and raise enduring questions about the extent to which medical intervention may inadvertently cause harm.
They also raise the troubling question of whether the contagious entity was necessarily the primary determinant of harm, or whether environmental conditions and medical notions of the time played a more decisive role.
Precisely what role each of the many factors played in smallpox — as well as in other diseases — in their severity and lethality is perhaps impossible to determine retrospectively, as the environmental conditions, health status of each individual, and the medical procedures to which a person was subjected on a case-by-case basis have been lost to history.
Nevertheless, what remains clear is that a simple contagion model does not fully explain the outcomes observed by these physicians across two centuries of practice.
This leads inexorably to a further conclusion: recording deaths from a specific disease, such as smallpox, does not necessarily capture the true cause of any particular death.
When such deaths are taken as an aggregate and compiled into local and national statistics, they can lead us to incorrectly assume that, in the case of these diseases, there was a simple one-to-one correlation — that a person died of smallpox without any consideration of the other vital factors: their environment, individual health status, and the medical interventions they experienced.
As Thomas Kuhn observed in his study of scientific revolutions, a challenge to an established theory is often dismissed or explained away rather than allowed to question the paradigm itself.
He wrote that his fundamental objective was to urge a change in the perception and evaluation of familiar data.[26] Viewing disease mortality statistics through a different lens — beyond the single-microbe mortality paradigm — is precisely such a challenge.
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