Germs, Genes, & Civilization: How Epidemics Shaped Who We Are Today

by David P. Clark

  Despite the hysteria associated with mad cow disease, the number of casualties is very small compared to those who die from more mundane food poisoning from bacteria or viruses. Perhaps the abnormal fear stems from the incurable nature of this disease.

  Fungal diseases and death in the countryside

  By and large, fungi have gotten a raw deal when it comes to sharing credit for causing disease and altering history. This is for three main reasons. First, fungal infections today generally range from the irritating to the embarrassing, from athlete’s foot to vaginal yeast infections. Few people nowadays die of fungal infections. Second, when we think about historical diseases, we tend to focus on spectacular epidemics such as the Black Death, which depopulated Europe in the 1300s, or the smallpox that decimated the Aztecs. Slower-moving diseases attract less interest. Third, in modern societies, little difference remains between town and countryside—everyone has electric lights, flush toilets, and iPods. In addition, we have far more historical records from towns and cities than from rural areas. Consequently, we wrongly assume that medieval peasants died from the same causes as their city-dwelling brothers.

  Highly virulent diseases such as plague and smallpox ravaged the crowded city populations of medieval times. Once a vigorous epidemic had started, fleeing townsmen likely carried it into the countryside. Nonetheless, quite a few isolated villages totally missed out on the Black Death, even during the most severe epidemics. Overall, rural areas had less disease, more because of the absence of overcrowding than because of sanitation. Consequently, the population often increased in rural areas even as it declined in the cities.

  Although life was healthier in the countryside, we should not be misled by poetic descriptions of pastoral bliss. Although the death rate in rural medieval England was significantly lower than in the towns, it was still atrociously high by modern standards. Life expectancy was around 30 years. A typical pair of medieval peasants might produce a dozen children, yet only three or four survived, hence rural population growth. Medieval peasants endured a life of hard work in unhygienic conditions. They were badly housed and often malnourished. In contrast to city folk, their major exposure to infection was from the microorganisms infecting their livestock and crops. In particular, the major culprits were fungal.

  Fungal diseases and cereal crops

  Cereal crops such as wheat, barley, rye, and millet are all highly susceptible to diseases caused by microscopic fungi. Such fungi might live as single cells (yeasts and plant rusts) or as thin, multicelled filaments (molds). Most diseases of major crop plants are fungal and are spread by spores carried in air or water. These diseases go by names such as molds, mildews, smuts, rusts, scalds, blotches, blights, and so forth. Although such diseases are unfamiliar nowadays, their short Anglo-Saxon names reveal that these diseases were familiar to ordinary people over many generations.

  When grain is harvested and threshed, fungal spores are tossed into the air. When these chores are done by manual labor, the workers breathe in the spores. In the industrial world we are still familiar with black-lung disease of miners. Here, coal dust is breathed in and causes severe irritation and inflammation of the lungs. However, coal particles do not grow and divide. Fungal spores do. If a healthy, well-fed person, who lives in clean, dry, warm housing breathes in a lungful of fungal spores, he might suffer minor irritation, but little else. If you are cold, wet, and poorly fed, the fungal spores will take advantage of your weakness to germinate. They will grow into fungal filaments, which penetrate deep into the lung, destroying human tissue and using the nutrients for their own growth. Once a fungal infection has taken root, there is little chance of dislodging it.

  Although fungal infections of the body surface are rarely dangerous, invasive fungal infections are often fatal, even today. Aspergillus is a common mold that occasionally invades the tissues of hospitalized patients who are severely weakened by other conditions. More than half of patients whose internal tissues had been invaded by Aspergillus died within 3 months, despite treatment with modern antifungal agents.

  In medieval times, sooner or later, a poor harvest would come. People would have too little food to last the winter and would be seriously weakened. Add to this a cold, wet winter and inadequate shelter. Any fungal spores waiting in the lungs would see the situation as a heaven-sent opportunity to germinate and get established. So during the Middle Ages, most agricultural workers (that is, the majority of the adult population) probably eventually died of fungal lung infections.

  As technology improved over the centuries, farming became more efficient and agricultural workers came into less intimate contact with spore-bearing grain. Better technology also decreased fungal infection of crops. This both decreased crop losses and reduced the risk of human infection. Farm workers came to live longer and to produce the greater amounts of food needed to feed a larger population. Nowadays, so few humans die of fungal infections that they have almost been forgotten.

  Religious mania induced by fungi

  Strangely, a few fungi that infect crops also affected religious behavior in medieval times. This was due not to a massive death toll undermining religious faith, but to a direct effect on the nervous system. The ergot fungus, which grows on cereals, especially rye, produces toxic alkaloids. High doses cause madness or death, but smaller doses cause hallucinations and bizarre behavior.

  The ergot alkaloids are a complex mixture of lysergic acid derivatives. The notorious hallucinogen LSD is a semiartificial derivative of lysergic acid. A crude mixture of ergot alkaloids was sometimes used in earlier times to induce childbirth. The effects were erratic because the level of alkaloids in different fungal extracts varied markedly, and this use has been abandoned. However, lysergic acid propanolamide is still sometimes used to control bleeding after childbirth.

  The ergot fungus, Claviceps purpurea, produces a brown to purplish body that replaces the grain in infected plants. Ergot-infected rye was often made into bread, and outbreaks of poisoning were frequent in medieval times. The severity varied, depending on the amount of contamination and the strain of fungus. Rye was not cultivated on a large scale until around the fifth century, in Eastern Europe and western Russia. From there, rye spread to the rest of Europe. During the Middle Ages, the symptoms of ergot poisoning, but not the cause, became well known. France was especially susceptible because rye was the major crop, and the mild, wet climate helped spread the fungus. In 944 A.D., about 40,000 people died of ergot poisoning in the south of France. Major outbreaks of ergot poisoning then occurred every five to ten years throughout large areas of France and Germany until the 1300s.

  Poisoning occurred in two main forms. The most common was called ignis sacer (Latin for “holy fire”) or St. Anthony’s fire, due to burning sensations in the extremities. In severe cases, the constriction of blood vessels caused gangrene of the arms and legs. This resulted in slow and painful loss of the limbs, which in medieval times was usually fatal. The second form caused convulsions and bizarre behavior. Although less common, the convulsive form probably affected society more. It gave rise to outbreaks of dancing mania. The earliest major example occurred in Aix-la-Chapelle, France, in summer 1374, with other episodes occurring over the next half-century.

  The authorities responded by playing music because this was believed at the time to have a soothing and curative effect on madness. In this case, the demented victims danced on to the music. Occasionally, the dancers fell out with the religious authorities, and in Liege they ended up cursing the priests. More often the dancers had a variety of hallucinations, which took orthodox religious forms, such as visions of the heavens opening to show Christ and the Virgin Mary enthroned in splendor. Overall, such visions tended to validate religious belief.

  The witch hunts of medieval days might also have been partly the result of ergot poisoning. In this case, milder and sporadic poisoning was involved. What evidence is there that the witch hunts were due to ergot instead of mere superstition? First, most witch tr
ials occurred in regions where rye was the staple cereal crop. Second, the number of witch trials was higher in years when there was a poor rye crop. When food was scarce, poor people had little choice but to consume grain of poor quality, even if it was contaminated with fungus. Trials were also more frequent in years when the weather favored the spread of the ergot fungus—that is, cooler and wetter than normal. By the nineteenth century, major outbreaks of ergot poisoning were largely restricted to Russia. The death rate in some of these outbreaks was as high as 40%. Ergot poisoning might also have triggered the famous Salem witch trials of America. The settlers in the Boston area grew rye under conditions that would have favored ergot.

  Although the people of the Middle Ages did not understand the cause of disease, bitter experience had taught them to regard plagues as contagious. When they encountered illnesses that apparently struck at random, such as epilepsy or the bizarre behavior from ergot toxicity, they tended to invoke religious explanations, such as possession by evil spirits or the effect of a witch’s curse. The victims of ergot poisoning were often regarded as the victims of witchcraft, not as witches themselves. Some other unfortunate wretch would often be blamed—perhaps a physician who was suspiciously effective in providing relief to the afflicted. Before laughing too loudly about the credulity of medieval peasants, remember that a substantial proportion of today’s Americans believe that little gray aliens in flying saucers visit Earth on a regular basis. Why is there no tangible evidence of this? Naturally, a conspiracy—not of Satanists, but of government officials!

  Over the past few hundred years, rye has been phased out and gradually replaced by wheat or barley. Today rye makes up a relatively minor proportion of the cereals grown. Is the resultant decrease in ergot poisoning partly responsible for the corresponding decline in religious belief? Is it just coincidence that the colder, northwestern parts of Europe, where wheat and barley were preferred over rye, have tended to adopt the plainer Protestantism, whereas both Catholic and Eastern Orthodox Christianity have more decorative images and icons of saints and angels? Such cultural issues are complex, but perhaps biology plays a greater role than previously suspected.

  Catastrophes caused by fungi

  During the Middle Ages, fungal infections took a steady, continual toll rather than appearing from time to time in virulent epidemics. As with malaria in tropical areas, they rarely caused specific catastrophes, but provided the backdrop to daily life—and death. Nonetheless, fungal diseases have sometimes caused historical catastrophes by destroying crops instead of attacking humans directly.

  The best-known case is the Irish Potato Famine of 1845–50, which was caused by the fungus Phytophthora infestans, the agent of potato blight. The blight appeared in Ireland in 1845 and destroyed about 40% of the potato crop. The following year, the entire crop was wiped out. In 1845, the population of Ireland was approximately 8.8 million. By 1851, it had dropped by about 30%, due to the loss of 2.5 million people. About half had died; the other half had emigrated.

  The potato blight also destroyed most of the potato crops of North America and Western Europe during the same period. The inhabitants of these other regions were less affected because they grew a mixture of crops, including cereals. In Scotland and Scandinavia, the cold winters killed the fungus and the potatoes survived largely unscathed. The Irish suffered most because they had become almost totally dependent on the potato alone.

  Rather than describe the history of the potato blight, let us relate this disaster to human disease. The potato blight parallels the effect of virulent plagues on humans. Dense populations of identical or related individuals are susceptible to massive infection and death. As human settlements have grown denser, so have their crops. Worse, many crops are genetically identical, or nearly so, because of centuries of selection for improved properties. This so-called monoculture is highly vulnerable to emerging epidemics.

  Human disease follows malnutrition

  Another link to human infection is that most of the victims of the potato famine died of disease rather than actual starvation. Lack of food weakened the famine victims, making them easy targets for infection. As the famine proceeded, hordes of starving refugees left their devastated fields for government workhouses. Here they crowded together in conditions that were not so much unhygienic as prehygienic.

  The two main killers were typhus fever and cholera. Typhus fever is spread by lice, ticks and fleas. We describe typhus fever at greater length when we discuss its destruction of Napoleon’s Grand Army during his failed attempt to invade Russia (see Chapter 6, “Pestilence and Warfare”). The bacteria that cause cholera and dysentery are spread by water contaminated with human waste. These bacteria all cause diarrhea and are spread by it. Even modern refugee camps run by the Red Cross frequently suffer outbreaks of dysentery or cholera. Some 50% to 60% of the deaths among present-day African refugees are the result of such diseases.

  Coffee or tea?

  Just as potatoes are associated with the Irish, tea is a symbol of British culture. Although tea was important from early colonial times, until the middle 1800s, the British drank more coffee than tea. The switch from coffee to tea was largely due to another fungus, the coffee leaf rust, Hemileia vastatrix. Unlike many fungi, coffee leaf rust is highly specialized and infects only coffee. It can be recognized by the yellow-orange powdery spots on the underside of leaves.

  Both coffee and its fungal enemy come from North Africa, especially Ethiopia. From there, coffee was taken to many European colonies. In particular, massive jungle clearing for coffee plantations was done in Ceylon (Sri Lanka). The rust soon followed. A British explorer in Kenya first saw coffee leaf rust in 1861. In 1867, the rust hit Ceylon and quickly spread to other countries. The destruction of the major cash crop during the next decade led to economic problems. Several British colonies changed to tea production instead. And so the British switched to drinking tea instead of coffee. During the nineteenth century, British soldiers abroad even made a remedy for intestinal problems by stirring a spoonful of gunpowder into a cup of tea.

  For the next 100 years, coffee leaf rust was restricted to Africa and Asia, but South America remained rust free. Then in 1970, the rust appeared in the Western Hemisphere for the first time, in Brazil. Within 20 years, it spread to the rest of South America and the Caribbean. In today’s world, coffee beans are the second most valuable international commodity, after oil, and the rust is controlled by fungicides. Curiously, the coffee leaf rust fungus is itself the victim of parasitism by other fungi. These grow on the rust and destroy many of its spores. Whether these “hyperparasites” could be used as biological control agents remains untested.

  Opportunistic fungal pathogens

  As noted, because fungi cause few deaths in industrial nations today, their role in infectious disease has been neglected. Recently, the infection of AIDS patients by a variety of opportunistic diseases, including fungi, has reawakened interest in fungal disease. Opportunistic diseases result from microorganisms that are harmless to healthy humans but that, as their name indicates, seize the opportunity to kick you when you are down. They include viruses, bacteria, and protozoa, as well as fungi.

  Fungal spores rarely penetrate unbroken skin or an undamaged intestinal lining. The vast majority of fungal infections enter via the lungs. To penetrate the finer airways of the lung, spores must be less than about two-millionths of a meter in diameter. Larger particles are trapped and swallowed or coughed out. A wide variety of fungi can cause similar lung infections, although they are rarely able to establish a foothold in the healthy and well fed. These fungi normally live on dead and decaying organic matter. Thus, they rarely possess mechanisms for causing disease in living victims. If by chance they land on organic matter that shows little sign of vigorous life and self-defense, they simply start to feed.

  Friend or enemy

  The fungi are not our enemies, nor are they our friends. A fungus does what it must to survive. Sometimes this conflicts with mankind
’s vested interests, but other times the fungi help us, although not intentionally. In the human war against infectious disease, fungi have been one of our most helpful allies. This is because fungi are just as capable of killing bacteria as they are of destroying potatoes or rotting the lungs of a malnourished peasant.

  Fungi kill bacteria by secreting chemicals known as antibiotics. The most famous family of antibiotics, the penicillin family, is made by molds. Penicillin is produced by the bread mold, Penicillium notatum, after which it was named. Since its discovery in the mid–twentieth century, penicillin has saved many millions of lives, far more than the relatively small number lost by the action of malicious fungi, either by direct attack or via crop loss and ensuing starvation. Unfortunately, a growing problem nowadays is the development of antibiotic resistance among many disease-causing bacteria.

  6. Pestilence and warfare

  Who kills more?

  Although we humans pride ourselves on our ability to destroy each other, most war casualties have been the result of infections, not enemy action. No, not infected wounds, either. Nowadays bullet holes and stab wounds are rarely fatal unless they hit a vital organ. Before antiseptics and antibiotics were available, however, wounds often became infected and frequently resulted in the loss of life or limb. Nonetheless, most casualties before modern times resulted from infections that killed soldiers who had not been wounded in combat—very often soldiers who had not even gotten into combat. Only since the twentieth century have improved hygiene and, to a lesser extent, enhanced firepower allowed humans to kill more people than microbes have.