Historic Dispute: Were yellow fever epidemics the product of locally generated miasmas

views updated

MEDICINE

Historic Dispute: Were yellow fever epidemics the product of locally generated miasmas?

Viewpoint: Yes, prior to the twentieth century, most physicians thought that yellow fever epidemics were the product of environmental factors, including locally generated miasmas.

Viewpoint: No, yellow fever epidemics were not the product of locally generated miasmas; evidence eventually proved that yellow fever is spread by the mosquito Aedes aegypti.

The origin of yellow fever is almost as mysterious and controversial as that of syphilis and concerns the same problem of Old World versus New World distribution of disease in pre-Columbian times. Until the twentieth century, the cause and means of transmission of the disease were also the subjects of intense debate. Some historians believed that the Mayan civilization was destroyed by yellow fever and that epidemics of this disease occurred in Vera Cruz and Santo Domingo (Hispaniola) between 1493 and 1496. Others argue that the first yellow fever epidemics in the Americas occurred in the 1640s in Cuba and Barbados and that the disease came from Africa. Waves of epidemic yellow fever apparently occurred throughout the Caribbean Islands during the seventeenth and eighteenth centuries. By the eighteenth century, yellow fever was one of the most feared diseases in the Americas. In the United States, yellow fever epidemics always broke out in the summer or autumn and disappeared rapidly as the weather turned cold. In some tropical zones, however, the disease was never absent.

Epidemiologists say that "humans suffer most from those illnesses for which they are not the intended host." This is true for yellow fever, which is transmitted to humans by mosquitoes from its normal reservoir in nonhuman primates. Some aspects of the eighteenth and nineteenth century debates about the cause of yellow fever epidemics can be clarified by reviewing current knowledge of the disease. Yellow fever is an acute viral disease usually transmitted to humans by the mosquito now called Aedes aegypti. Jungle yellow fever remains endemic in tropical Africa and the Americas, but historically, the urban or epidemic form has been most important. Dense populations of humans or other primates are needed for transmission of the disease from one victim to another. The mosquito, which only bites when the temperature is about 62°F (16°C), has a very limited range and needs stagnant water to live and breed. However, the mosquito hibernates during periods of low temperature, and the eggs can withstand severe drying condition for several moths before hatching. The virus must be incubated in a mosquito for 9 to 18 days before the mosquito can infect another person.

During the first stage of the disease the virus circulates in the blood and a mosquito can become infected by biting the patient. Chills, headache, severe pains in the back and limbs, sore throat, nausea, and fever appear after an incubation period of three to four days. Physicians who were well acquainted with the disease might note subtle diagnostic clues such as swollen lips, inflamed eyes, intense flushing of the face, and early manifestations of jaundice. The second stage was an often deceptive period of remission, in which the fever diminished and the symptoms seemed to subside. In many patients, however, the disease would enter the third phase, which was marked by fever, delirium, jaundice, and the "black vomit." Death, with profound jaundice, was usually caused by liver failure, but the disease could also damage the kidneys and heart. In the absence of modern diagnostic aids, physicians often found it difficult to distinguish between yellow fever, dengue fever, malaria, and influenza. Since many diseases may coexist in impoverished tropical countries where yellow fever is most common, differential diagnosis remained a problem well into the twentieth century. Because yellow fever is caused by a virus, no specific remedies have ever been available. Complete rest, good nursing care, and symptomatic relief, remain the most effective therapies.

Determining the mortality rate of yellow fever is difficult because many mild cases may not be reported. Estimates in various epidemics have ranged from 10% to as high as 85%. Statistics from some nineteenth century hospitals reveal mortality rates as high as 50%. However, physicians generally claimed that the mortality rate for their private patients was closer to 10%. Presumably these differences reflect the different health statuses of wealthy private patients and poor hospitalized patients.

Despite the antiquity of yellow fever epidemics, the cause and means of dissemination of the disease were not understood until the twentieth century. Nevertheless, debates about the nature of the disease and the best method of treatment and control were widespread and sometimes hostile. Most eighteenth and nineteenth century physicians thought that endemic and epidemic diseases were caused by environmental conditions, especially bad air, heat, humidity, and filth. Thus, the collection of meteorological and geographical information was of great interest to physicians who hoped to find the critical correlations between disease and environmental factors.

Debates about the causes and means of dissemination of disease, however, included contagion theory as well as the miasma theory. Contagion referred to transfer by contact. The idea that disease, impurity, or corruption can be transmitted by contact is very old, but it was generally ignored in the Hippocratic texts. According to the miasma theory, disease was caused by noxious vapors that mixed with and poisoned the air. The Italian physician Girolamo Fracastoro (1478-1553) published a classic description of these theories in 1546. In De contagione et contagiosis morbis (On Contagion and Contagious Diseases), Fracastoro proposed an early version of the germ theory. He suggested that diseases were caused by invisible "seeds." Some diseases, such as syphilis and gonorrhea, were only spread by direct contact, whereas other diseases, such as malaria, were transmitted by noxious airs. The seeds of some diseases, however, could contaminate articles that came in contact with the sick person. These articles, usually referred to as fomites, could then cause sickness in another person. Although seventeenth century microscopists had seen bacteria, protozoa, and molds, the connection between microorganisms and disease was not established until the second half of the nineteenth century.

Even during the "golden age" of medical microbiology in the late nineteenth century, the contagion/miasma controversy concerning yellow fever could not be resolved until studies of insect vectors explained the chain of transmission. Ancient writers had speculated about the role of insects in the transmission of disease, but scientific confirmation was not established until the late nineteenth century through the work of British parasitologist Sir Patrick Manson and the bacteriologist Sir Ronald Ross. Nevertheless, several clues to the puzzle of yellow fever had been collected long before the "mosquito theory" was subjected to experimental trials.

Yellow fever became a disease of special interest to the United States as a result of the Spanish American War in 1898. After the war, the U.S. Army occupying Cuba found yellow fever a constant threat. Improvements in the sanitary status of the island failed to decrease the threat of yellow fever. In 1900 a special commission, headed by Major Walter Reed, a U.S. Army pathologist and bacteriologist, was sent to investigate the causes of infectious diseases in Cuba. Following leads provided by a Cuban epidemiologist, Carlos J. Finlay, Reed and his colleagues carried out carefully controlled experiments to determine whether yellow fever was transmitted by miasma, direct contagion, or the bite of infected mosquitoes. Reed's results clearly disproved the miasma theory and established rigorous proof that the disease was transmitted by the bite of infected mosquitoes.

Acceptance of the mosquito theory made efforts to control yellow fever possible, but did not fully eliminate the threat of this viral disease. The discovery of jungle yellow fever in the 1930s among tree-dwelling primates in South America and Africa meant that an inexhaustible reservoir of disease would thwart all efforts at eradication. Safe and effective yellow fever vaccines were not widely available until the 1940s. Epidemics of yellow fever in Africa in the 1970s stimulated renewed interest in the yellow fever virus. The disease also remains a threat in South America. The reservoir of yellow fever virus in South American rain forests and the resurgence of Aedes aegypti in urban areas led some public health specialists to warn that it is only a matter of time before urban centers again experience the threat of yellow fever. Mysteries about the distribution of the disease remain. For example, the disease is unknown in Asia even though Aedes aegypti are common.

The 1793 yellow fever epidemic in Philadelphia, which was then the capital of the new republic, was the first major outbreak in the United States. Later epidemics occurred in New York, Baltimore, Norfolk, and other urban centers. The effect of this epidemic on Philadelphia, and on medical thought and practice, were profound, as indicated by the debates about whether the epidemic was the product of locally generated miasmas.

Yellow fever epidemics have been studied from many perspectives. Historians have been especially interested in examining the relationship between health, politics, public health regulations, professionalism and medical practice, especially during times of crisis in the early days of the United States. The debate about the cause of yellow fever was much more complex than a debate between narrow interpretations of contagion and miasma.

The controversy about the origins and treatment of yellow fever in Philadelphia became part of the wider political debates of the 1790s, i.e., the conflict for political leadership between supporters of Alexander Hamilton (George Washington's secretary of the treasury), who advocated a strong central government, and those of Thomas Jefferson, who did not. Perhaps because Philadelphia was home to the most learned medical community in the nation, the debates about the epidemic were particularly heated, and, because of the political climate, often quite hostile. Even decisions about treatment regimens became embroiled in political disputes. Nevertheless, neither side could provide conclusive proof as to whether the disease was the product of contagion or miasma, imported or generated by local conditions. After the epidemic of 1793, Philadelphia reached for a pragmatic compromise and attempted to institute both quarantine and sanitary reforms when dealing with later epidemics. Although yellow fever no longer excites the fear that it inspired in the eighteenth century, understanding the historical debate about this disease might provide cautionary lessons for dealing with the threat of West Nile fever in New York and other parts of the United States.

—LOIS N. MAGNER

Viewpoint: Yes, prior to the twentieth century, most physicians thought that yellow fever epidemics were the product of environmental factors, including locally generated miasmas.

When a community is struck by epidemic disease, one of the first priorities is to identify the source of the illness. By being able to explain how the epidemic started, those responsible for public health can take action to contain the epidemic and prevent future outbreaks. In the case of the epidemics of yellow fever that struck the urban centers of Europe and the Americas during the eighteenth and nineteenth centuries, the debate over etiology reflected some of the fundamental issues in Western medical theory at this time. Until the middle of the nineteenth century, most medical observers were convinced that yellow fever epidemics were the result of locally generated miasmas. This was not a new medical theory, but part of a long tradition, dating back to early Greek medicine. Many of the epidemiological characteristics of yellow fever, how it appeared and spread through the community, were puzzling to physicians and public officials. As a result, they examined their surroundings and tried to construct explanations that were rooted in the specific conditions that they found in their urban environments. The hypothesis that epidemics of yellow fever were the products of locally generated miasmas was convincing, because it accounted for many aspects of the epidemics that the idea of an outside contagion, spread from person to person, could not. Therefore, many people in the early nineteenth century regarded it as the most convincing explanation for the epidemics that threatened their communities.

Miasma and the Environment

For many centuries, the concept of miasma had been important in debate over the causes of disease. Miasma is a Greek term, which in its most basic sense referred to any kind of pollution or polluting agent. In regard to late eighteenth and early nineteenth discussions about disease, the term specifically referred to noxious vapors that tainted the air, causing yellow fever and other epidemic diseases. These vapors could arise from various sources, such as stagnant water and marshes, dead animals or corpses, rotting food and vegetable matter and any other kind of filth or decaying material. Once the air was polluted in this manner, it could have an adverse effect on the human body, resulting in illnesses throughout the community. Changes in weather conditions could also affect the air, producing miasmas that could create epidemics. For this reason, many epidemics were associated with climatic events, such as great thunderstorms.

Those medical theorists who argued that yellow fever was the product of local miasmas had centuries of medical theory to support their arguments, reaching back to antiquity. Theories of miasma are to be found amongst the Hippocratic writings of early Greek medicine, as part of their general focus on the role of the environment in causing disease in the human body. The main thrust of this approach is that the source of disease exists not within the sick person, but in the external environmental conditions, which create pathological changes within the human body. In particular, many early medical writings put a great deal of emphasis on the role of the air in affecting health and causing disease. As the human body is dependent upon air for life, and because air is everywhere, the idea that polluted air could cause epidemic disease has always been very compelling. Identifying the air as the source of disease provided an ideal explanation for the simultaneous appearance of the same disease in many different people, which made it particularly relevant in understanding disease epidemics.

Urban Society: Filth and Fear

The theory of miasmas was also compelling as an explanation for disease to people who were concerned about the conditions of urban life in the eighteenth and nineteenth centuries. Given the lack of adequate sewerage systems or a means of disposing of household and industrial wastes, cities were places of foul smells and disgusting filth. In the era before the knowledge of the role of bacteria in causing disease, the effect of the filthy environment upon the air was the major public health concern. It required little imagination on the part of concerned citizens to believe that the piles of rotting offal and carcasses of dead animals that accumulated in the streets could let off stinking fumes that would taint the air and cause diseases. In Philadelphia during the 1793 yellow fever epidemic, observers criticized the usual methods of disposing of household wastes and food scraps, because they created a poisonous stench that had an unhealthy effect on the air.

Sanitation was therefore a crucial issue for those who believed that epidemics were a product of unclean conditions. When cases of yellow fever would start to appear in a city, one of the first actions usually taken by city officials was to order the streets to be cleaned up. The threat of yellow fever within a city inevitably brought with it criticism of public cleaning measures. Often, epidemics were blamed upon the laziness and ignorance of public officials, whom people held responsible for the filthy conditions that were believed to create epidemics. Such criticisms indicate the close association in many people's minds between the local environmental conditions and disease epidemics. Therefore, urban officials came under increased pressure during the nineteenth century to provide a hygienic environment for their citizens.

Philadelphia 1792

The yellow fever epidemic that struck Philadelphia in 1792 was not the largest in terms of loss of life, but it was significant for a number of reasons. Philadelphia was the capital of the United States at the time and the major political and economic center of the young nation. As a result, it was also home to some of the leading physicians in the country. This was the first major epidemic of yellow fever to strike a United States city, and it highlighted crucial divisions between medical thinkers. Physicians split over the issue of whether the disease was a contagion that had been brought in from outside the city, or whether it had arisen within the city as a result of the conditions there. Many people claimed the disease had been imported with shiploads of French refugees escaping a revolution on the Caribbean island of Hispaniola (now Haiti and the Dominican Republic). However, a prominent Philadelphia physician, Dr. Benjamin Rush, argued in favor of the local origins. Rush regarded the disease as a product of conditions within Philadelphia, and particularly pointed the finger at a cargo of rotting coffee that had been left for weeks on the wharves near the neighborhood where the first cases of fever were reported. This refuse had created a noxious miasma that polluted the air, causing the epidemic.

This hypothesis did not meet universal acceptance from Rush's medical peers. The Philadelphia College of Physicians, which represented medical authority in the area, maintained the disease was an outside contagion. However, there were a number of reasons why Rush's explanation of the cause of the epidemic was compelling. First, the pattern of the spread of the disease did not support the theory that the disease had been transmitted from person to person through direct physical contact. People in various parts of the city contracted the disease simultaneously, without any chain of direct contact between them. In an age before an understanding of viruses and the role that mosquitoes played in spreading some diseases, there was no adequate theory of contagion that could explain how a yellow fever victim in one street could infect another person living two streets away without any physical contact. Therefore, the presence of a pathological element in the general atmosphere seemed to offer a more convincing explanation.

Secondly, those who attended the sick did not always contract the disease themselves. If the disease was contagious, why didn't everyone who had contact with the sick get it? One of Rush's students claimed that that various experiments, such as drinking the vomit of infected victims, were carried out during the epidemic to support the theory the disease was not contagious. The idea that the fever was a product of the local environment rather than carried by the victim and transmitted to others, was also supported by the fact that the disease did not spread out of Philadelphia. Those who contracted the disease and were taken outside the city did not appear to transmit it to others, and the epidemic was largely confined to the environs of the city. This seemed to suggest that the disease was a product of the specific conditions within Philadelphia that summer and autumn. Anticontagionists such as Rush pointed to these issues when arguing against the theory that the epidemic was caused by a contagion introduced from an outside source. To find the cause of the epidemic, people needed to look no further than the poisonous vapors produced by the refuse within their own city. The connection that was drawn between the epidemic and the specific local conditions of the city is reflected in part of a poem written by a local newspaper editor, Philip Freneau, during the epidemic:

Nature's poisons here collected
Water earth and air infected-
O, what a pity
Such a City
Was in such a place erected.

In the poem, the environmental conditions of Philadelphia itself, rather than external sources of infection, were being blamed for the disease.

Anticontagionists versus Contagionists

As epidemics of yellow fever became a regular occurrence in nineteenth-century urban life, anticontagionist arguments gained wide support in the medical community, both in the United States and in Europe. In the first half of the nineteenth century, many physicians were convinced that yellow fever was not contagious. Anticontagionists noted other details that seemed to support their position. Yellow fever epidemics usually occurred during the summer months, when the summer heat was most likely to cause putrefaction in the environment and create dangerous miasmas. The fever receded with the coming of colder weather, when the air was purified of noxious vapors by frost and colder temperatures. The connection between the incidence of epidemics and the seasons furthered encouraged people to identify environmental conditions as the source of the disease.

The failure of quarantines to prevent outbreaks of yellow fever was also seen as evidence that epidemics were created by conditions in the city, rather than being brought in from the outside. Quarantines had been part of the standard public health response to epidemic disease since the plagues of the Middle Ages, but anticontagionists argued that they were an unnecessary disruption to trade and commercial enterprise, therefore having a negative effect on morale during an epidemic. In response to claims that epidemics usually coincided with the arrival of ships from cities hit by yellow fever, they pointed to instances when quarantines against such ships had failed to prevent epidemics. Instead, anticontagionists focused upon preventing epidemics by eliminating the sources of the miasmas that caused disease, such as piles of filth and stagnant water. Ironically, such measures would have succeeded in destroying some of the habitat of the mosquito, which, unbe-known to medical theorists at the time, was the main culprit in the spread of yellow fever. The debates over the measures that should be taken in response to the threat of yellow fever continued for most of the nineteenth century.

Conclusion

As yellow fever became a regular feature of the urban environment in the nineteenth century, public health officials tried to take actions that might protect their communities from the disease. In most cases, sanitation measures were combined with quarantines in an effort to ward off the threat. However, while cities might enforce quarantines, the theory that the disease was spread from person to person was difficult to sustain, given the way an epidemic started and progressed. To many medical observers, locally generated miasmas provided the best explanation for the characteristics of a yellow fever epidemic. In the context of late eighteenth and early nineteenth century ideas about disease, Dr. Rush's claim that a rotting cargo of coffee could infect the quality of the air, which in turn could poison the human body, was convincing. Such theories also had the benefit of centuries of medical authority, an important consideration in eighteenth and nineteenth century medicine. Most of all, the explanation was compelling because it offered an explanation which was rooted in the contemporary understanding of the interaction between the environment, the air, and the human body in causing disease.

—KATRINA FORD

Viewpoint: No, yellow fever epidemics are not the product of locally generated miasmas; yellow fever is spread by the mosquito Aedes aegypti.

Physicians in the late eighteenth and nineteenth centuries were divided over the etiology and epidemiology of yellow fever. Debate centered on the question of the origins of yellow fever epidemics. Were they a product of miasmas, poisons that arose from the fetid environmental conditions and tainted the air? Or was yellow fever a contagion, carried into an area by an infected person and spread to others? For many medical observers, the idea that such a terrible disease could be a product of the local conditions was unthinkable. Instead, they regarded the disease as foreign, something that was brought into the community from the outside. As a result, local authorities enforced quarantines to protect an area from epidemics that might be raging in other cities and towns. However, the argument that miasmas were the cause of epidemics had centuries of medical authority in its favor, and had broad support among medical experts in the early nineteenth century. Yet, as medical research began to focus on the search for the specific microscopic entities that caused diseases, the theory of miasmas became outmoded. Finally, the discovery and confirmation of the role of the mosquito as a vector in spreading the virus that causes yellow fever rendered both miasmas and earlier ideas of contagion obsolete in explaining yellow fever epidemics.

Contagion

Like the theory of miasmas, the concept of contagion has had a long and complex role in the history of medical thought. The term generally referred to a disease that could be passed from person to person, causing the same illness in each one. However, in an age before scientists understood how specific diseases were caused by bacteria or viruses, exactly how a disease could be transferred from one person to another was a source of enormous debate and inquiry. Nevertheless, in the case of epidemic illness in the eighteenth century, it was generally thought that such diseases were contagious. The measures that communities took against epidemics were based on the belief that physical contact with a sick person would cause another person to become ill. Therefore, for an epidemic of a disease such as yellow fever to occur in an area where the disease had not existed before, it was believed that it had to have been carried from the outside by an infected person.

It was not difficult for communities to identify foreign sources of the yellow fever contagion. In the case of the 1793 epidemic in Philadelphia, the recent arrival of refugees from the island of Hispaniola in the Caribbean, an area notoriously infested with yellow fever, was regarded by many prominent physicians as the source of the epidemic. Later epidemics in the cities of the American South were also traced to the arrival of ships and trade from the fever zones of the Caribbean and South America. Such beliefs were no doubt informed by xenophobia and parochialism. Communities have always tended to blame outbreaks of diseases on foreign scapegoats, and people also feared the damage the belief that the disease had arisen out of an unhealthy environment could do to the reputation and economic growth of their city. However, the idea the disease was a contagion was also founded on the observation that epidemics appeared to develop following the arrival of ships, goods, and people from other infected areas.

Many medical theorists challenged the belief that yellow fever was a contagion. During the 1793 Philadelphia epidemic, Dr. Benjamin Rush argued that yellow fever was the result of miasmas produced by a filthy environment. While Rush met opposition for his theories, particularly from the Philadelphia College of Physicians, anticontagionist ideas gained support amongst many physicians and medical theorists in the early nineteenth century. However, popular belief continued to assume that the disease was a contagion and could be caught through contact with an infected person. Contemporary accounts of the Philadelphia epidemic indicate that people were convinced that the disease could be caught through physical contact. People avoided friends and acquaintances in the street and shaking hands was frowned upon for fear it would spread the disease. Some observers also noted the cruel treatment that Philadelphians received from people outside the city, due to the popular fear that they carried the disease and could spread it to others. While miasmas may have gained ground among medical observers as an explanation for yellow fever, quarantines against people and goods from infected areas continued to be enforced by cities in North America and Europe. This indicates a continued belief in the contagious nature of the disease, despite what medical wisdom may have claimed.

The Decline of Miasma

By the middle of the nineteenth century, as yellow fever ravaged communities in the American South, serious doubts were raised about the theory that epidemics were caused by locally generated miasmas. Some observers questioned the association between yellow fever and a dirty environment, particularly when a city contained all the elements that supposedly generated miasmas, but no outbreak of the disease occurred. Such questions raised important issues. If the disease was a product of miasmas rising from putrefying filth, why did outbreaks not occur whenever such pollution was present? It was not clear why some towns had epidemics while others, with the same or even worse sanitary conditions, might escape altogether. It was becoming apparent to many people that miasmas from rotten garbage and filth were alone not enough to explain an outbreak of yellow fever. There had to be some other factor or element present to account for an epidemic. However, exactly what that factor was remained unresolved, and produced much debate and speculation until the beginning of the twentieth century.

Medical observers were also coming to be accept that the disease, if not directly contagious, was at least transportable. Although it did not seem to spread directly from person to person, it was apparent that epidemics did follow transport routes, from port to port, along railway tracks, and up rivers. In particular, in a variant of the idea of contagion, clothes and possessions that had come into contact with yellow fever victims were believed to be the major culprit in transporting the disease, rather than the people themselves. The idea that the disease was transportable was not always inconsistent with the emphasis placed upon the role of the local environment. Many claimed that while the disease could be imported into an area, local conditions determined whether an epidemic would take hold. Others remained committed to the idea that epidemics in some cities arose as a result of poisonous exhalations from urban filth, but allowed that the disease could then be spread to other towns and cities through infected goods. In the attempt to provide explanations for the characteristics of yellow fever epidemics, miasma and contagion were not necessarily contradictory approaches. This justified the combination of sanitation and quarantine measures in fighting off the threat of yellow fever.

The increasing focus of medicine in the nineteenth century upon specific diseases, was important to the development of new epidemiological theories. Previously, diseases were generally not conceived of as specific things with particular causes and cures. Yellow fever was regarded as but one of the many types of disease classed as fevers, which may have differed in their symptoms, but not in their essential causes. However, as physicians began to think about yellow fever and other illnesses such as malaria or cholera as distinct diseases, they began to focus on identifying the specific causes of these diseases. By the 1870s, medical opinion suggested that specific microscopic "yellow fever germs" were the cause of epidemics, not general miasmas that tainted the air. The hunt was on in the latter decades of the nineteenth century to identify this germ, although at this time, the exact definition of what a germ was varied widely. However, because it was believed that germs thrived in an unclean environment, filth and unhygienic conditions remained a focus for public health authorities attempting to prevent epidemics. A shift had occurred from seeing the environment as the source of miasmas that poisoned the air, to seeing it as the breeding ground for germs that spread the disease. As it turned out, both theories were incorrect.

The Hidden Culprit: A Mosquito

Some early observers of yellow fever had observed the connection between the onset of epidemics and the presence of large numbers of mosquitoes. This was explained by those who supported the theory of miasma as further evidence of the fetid and poisonous nature of the air. In 1881, the Cuban epidemiologist Dr. Carlos J. Finlay presented a paper that argued that yellow fever was spread by the mosquito Aedes aegypti. However, Finlay was unable to present experimental proof of his hypothesis, and nothing came of his theory until 1900, when a team of medical experts, headed by Dr. Walter Reed, a U.S. Army pathologist and bacteriologist, was appointed by the U.S. Medical Corps to investigate yellow fever epidemics and their causes. At this time, the U.S. Army bases in Cuba were badly affected by yellow fever epidemics, and the building of the Panama Canal was also being hindered. The Reed commission, with Finlay's help, carried out experiments to test the different hypotheses of the cause and transmission of the disease. In one experiment, a group of army volunteers was isolated in a hut with the bedding and clothing of yellow fever patients, while another group was housed in clean surroundings and exposed to the bite of a mosquito that had bitten a yellow fever patient. The first group remained healthy, while the second contacted the disease, putting to rest the argument that the disease was spread through contact with the clothing, bedding, and belongings of yellow fever victims.

These findings were developed into an intensive public health campaign by U.S. Army surgeon William Crawford Gorgas, who from 1898 to 1902 was in charge of sanitation measures in . in the Cuban city of Havana. Gorgas's campaign was based on exterminating the mosquito and its habitat within urban areas in Havana, and any source of standing water, such as jars, pitchers, basins, where the mosquito might breed, was destroyed. The army hierarchy and public health officials did not immediately accept Gorgas's campaign. Many ridiculed the idea that the disease was spread by the bite of the mosquito and criticized the campaign for ignoring the filth and rubbish that had traditionally been regarded as the source of yellow fever. However, Gorgas was able to practically eliminate yellow fever from Havana, and repeated this success in Panama, opening the way for the completion of the canal. A similar campaign was carried out in the last attack of yellow fever in the United States in New Orleans in 1905, where school children were rewarded for bringing in dead mosquitoes. The Reed commission had concluded that the agent causing the disease was a virus, although the exact identification and classification of the virus could not be established until the late 1920s. A vaccine for yellow fever was developed in the 1930s. Although the eradication of the mosquito means that yellow fever has disappeared from cities in the United States, it continues to be present in some tropical areas of the world, and travelers to these areas require vaccinations to be protected from the disease.

Without the knowledge of the role of mosquitoes in transmitting diseases, epidemics of yellow fever were profoundly baffling to physicians and other medical observers. Later developments in medical science showed that epidemics of yellow fever were not the result of miasmas generated in the local environment. The anticontagionists could not explain the connection of epidemics with the movement of people and goods, nor could they offer an explanation as to why communities had outbreaks in some years and not others. However, there was no model of contagion that could adequately account for the epidemiological characteristics of yellow fever. As ways of thinking about diseases and their causes were transformed in the nineteenth century, such hypotheses became inadequate as explanations for disease. Medical thought began to focus upon specific diseases and their causes, and the idea of miasmas was too vague and general to function as an adequate explanation for epidemics of yellow fever. It could be said that those who advocated the miasmas were correct in their belief that yellow fever was caused by an element present in the air. However, that element was not a poison produced by local wastes, but a virus made airborne within the body of its mosquito vector. In the late eighteenth century, such a suggestion would have seemed ludicrous to most medical theorists. A century later, it was basis of a public health campaign that led to the eradication of yellow fever from the cities of the Americas and the Caribbean.

—KATRINA FORD

KEY TERMS

CONTAGION:

Illness that can be spread from one person to another, usually through physical contact.

ENDEMIC:

Disease that occurs within a specific area, region, or locale.

ETIOLOGY:

Study of the nature and causes of disease.

EPIDEMIOLOGY:

Study of how diseases spread from person to person and from place to place.

HIPPOCRATIC TEXTS:

Collection of early medical writings which served as the basis of medical thought until the seventeenth century; named after the Greek physician Hippocrates (c. 460-377 b.c.), although not all of them were written by him.