The first major conflict in which more combatants were killed by other humans than by disease was the Russo-Japanese War of 1904–1906. Even here, this applied only to the cleaner and more hygienic Japanese. The Russians lost more men to disease than to enemy action, and they also lost the war. Whether World War I was a step forward is debatable. The armies on the western front were vaccinated and disinfected, and suffered most of their casualties from enemy action. The eastern front was quite a different story, and infectious disease retained the upper hand. By World War II, mankind had at last progressed to that point at which humans were more of a threat to human life than microorganisms.
Spread of disease by the military
Warfare is generally accompanied with an upsurge in infections, among both the military and surrounding civilian populations. Modern readers probably think the phrase “well-seasoned troops” refers to those with battle experience. Not so. In historical times, smart commanders gathered their recruits together and stayed somewhere safe and well supplied for a few months. During this period, the soldiers shared their infections and became “seasoned.” Being ill while properly fed and housed instead of in active service greatly reduced overall casualties from disease. We discussed the principles involved in the spread of disease in Chapter 3, “Transmission, Overcrowding, and Virulence.” Three factors are especially important in the spread of disease by warfare: crowding, mixing, and mobility.
• Crowding: Armies are crowds of men who eat, sleep, and work in close contact. Such conditions are ideal for the spread of disease. Moreover, hygiene is poor. Soldiers might be crowded together in camps, barracks, or trenches. Sailors are crowded on warships. Troop ships carrying soldiers packed like sardines are even more crowded. Only in recent times have hygienic measures been adopted. Very early in history, armies were doubtless dirty, but they were also relatively small and so were not especially prone to disease. As armies grew over the ages, they provided infectious disease with ever better conditions for spreading.
• Mixing: When armies are assembled, recruits gather from separate localities all over the nation or empire. As they mix together, they exchange their infections. Diseases previously confined to one locality or segment of the population are shared. During the American Civil War, about a third of the Northern troops fell ill before leaving their training camps, mostly due to intestinal ailments, including typhoid. In World War I, a similar proportion of draftees was rejected as unfit. Although the rural population was healthier, rural recruits fell prey to infections more often than those from towns and cities. The urban population had been exposed to diseases such as measles, mumps, chickenpox, diphtheria, scarlet fever, and tuberculosis early in life. Many rural folk, especially from remote areas, had never been exposed to these diseases. Thus, when these populations were mixed, the rural enlistees were vastly more susceptible.
• Mobility: Armies rarely stay put. Whether they advance, retreat, or merely march in circles, they carry infections with them. Armies carry disease across land, and navies carry disease across the seas. Even when armies are stationary, as in siege or trench warfare, new recruits are constantly drafted to the front and the sick are withdrawn. Prisoners transfer disease from one army to another, and deserters carry disease wherever they seek shelter. Infections are spread to civilians along the route of troop movements. In addition, wars often displace large numbers of civilian refugees, who flee to safety either individually or en masse. Ticks, mites, lice, and fleas travel with the humans they inhabit. Disruption caused by warfare also displaces rats and mice, which consequently move around with their accompanying fleas.
Another, though less universal, factor is the chaos generated by warfare, especially among the vanquished. This often leads to food shortages and malnutrition. Crops might be accidentally trampled, seized by the military, or deliberately destroyed. Poor nutrition weakens resistance to infection. Standards of hygiene lapse, especially among armies in retreat and civilian refugees. The chaos factor has probably had more impact in modern times. In medieval times and before, most people were unhygienic and malnourished anyway.
Is it better to besiege or to be besieged?
In the realm of disease, it is undeniably better to give than to receive. Being sealed in a castle or walled city with a lot of other grubby humans, horses, dogs, rats, mice, lice, and fleas was usually worse than attacking. The defenders were obliged to take their livestock inside (together with their diseases) if they wanted milk or fresh meat. The defenders were unable to get rid of human or animal waste unless they were willing to haul it to the top of the walls and pitch it over at the enemy. Sewage and refuse piled up. Dead bodies could not be buried. Rats scavenged in the garbage. Fresh water was scarce and often contaminated.
Although the odds definitely favored the attackers, the downfall of the defenders was by no means inevitable. If a crowded metropolis is besieged by soldiers from rural areas, the urban/rural exposure factor noted earlier might come into play. The city population will have built up resistance to disease, and the rural population will lack previous exposure. A few captives, deserters, or envoys from the city could spread a devastating epidemic among the encircling army.
The siege of Mecca by the Ethiopians (569–570 A.D.) and the siege of Jerusalem by the Assyrians (701 B.C.) are both cases in which the attacker was routed by pestilence and the siege therefore failed. Mohammed was born in A.D. 570, and Islam had not yet been founded. Nonetheless, Mecca was already the holy city of the Arabs, and the Ethiopian Christians were hoping to destroy Allah’s sacred shrine, the Ka’aba. An epidemic, probably smallpox, brought them to their knees and killed their leader, Abraha, who rode on a white elephant. In the Koran, we read this:
“Have you not considered how Allah dealt with the Army of the Elephant? Did he not foil their stratagem and send against them flocks of birds which pelted them with clay-stones, so that they became like plants cropped by cattle?”—The Elephant, The Koran
The Islamic expansion of the seventh and eighth centuries spread smallpox throughout the Mediterranean area. Or perhaps we might argue that smallpox cleared the way for Islam to expand, much as it later cleared the way for the European colonization of America. The Islamic Empire crossed from North Africa to conquer Spain in 710 and penetrated into France in 731. By this time, Europe had recovered from the colossal population die-off from the bubonic plague of Justinian’s day and was adjusting to smallpox. The Arabs failed to take France but held much of Spain until the next Black Death pandemic, in the mid-1300s. (Even then, the Moors held Granada until 1492, the year Columbus sailed for America.)
Sometimes disease declines to take sides and strikes down besieger and besieged alike. The siege of Kaffa, which resulted in the entry of the Black Death into Europe, is a case in point. The plague spread from the encircling Tartar army to the besieged Italians, demonstrating that epidemic disease is only too likely to travel from one army to another.
Disease promotes imperial expansion
“God is usually on the side of the big squadrons and against the small ones.”—Roger de Bussy-Rabutin (1618–1693)
As explained before, civilizations tend to develop resistance to epidemic disease that then acts as a protective shield. Dense populations acquire a repertoire of infectious diseases. The denser the population, the greater its repertoire. Provided that it survives the initial onslaught, its people gradually become resistant to many of these infections. When disease-adapted populations contact other civilizations, the infections are transferred. The result depends on how much previous exposure to these infections the recipients have had. If the recipients are from a sparser culture with no previous exposure, they will be devastated. The most spectacular example is the depopulation of the New World by European diseases. However, similar die-offs on a more restricted scale have probably accompanied the spread of all major civilizations.
Small tribes of early man domesticated dogs to guard against predators and help in hunting. We might view disea
ses as being domesticated by larger societies. After a dense population center has adapted to a particular infection, this domesticated disease will guard against intruders and help during missions of aggression. When a densely populated city forms, it will have an advantage over smaller neighboring communities. Infectious disease will spread from the big city and decimate the neighboring cultures. Their territory can then be absorbed with less military effort. The invaders will occupy the new territory. If the original inhabitants who remain are too few to regain independence, they will be assimilated and, in time, become citizens of the growing empire. The cycle can now repeat itself. After an imperial nucleus has formed, it tends to grow like a snowball rolling downhill.
The growth of the Roman Empire proceeded in much this manner. Rome absorbed neighboring villages, then small towns, then the other Italic states, and so on. The Romans had the good sense to extend citizenship to the people they assimilated, giving biology a helping hand. Eventually, the expanding Roman sphere came into contact with the other major Mediterranean civilizations and their diseases. Although the halo of urban disease still provided valuable protection against barbarian incursions, it was of little use against other major urban blocks, such as the Greeks or Carthaginians. From this point on, disease no longer favored the Romans. Ultimately, Rome expanded far enough to make contact with a series of novel diseases that had evolved among the dense populations of Asia. The outcome proved disastrous for the Romans. Several major yet still unidentified epidemics, followed by the bubonic plague, depopulated the Roman Empire. Doubtless, the Romans gave the combined disease repertoire of Europe and North Africa to Asia in exchange. This reciprocal export of infection seems to have caused depopulation not only for the Romans, but also for the Chinese Han Empire.
Protozoa help keep Africa black
The most prominent example of disease fighting for the less densely populated side is the special case of Africa. As the original homeland of mankind, Africa retains many of our ancient tropical diseases. Malaria, sleeping sickness, and yellow fever combined to protect sub-Saharan Africa from Arab invaders and then Europeans. The natives of Africa have evolved at least partial resistance to many tropical diseases, and although they still suffer a major disease burden, outsiders are vastly more susceptible.
Tropical diseases have also kept other tropical regions fairly isolated from world culture until recently. What is so special about tropical diseases? Malaria, sleeping sickness, yellow fever, and several less-well-known tropical infections all must be spread by insects that cannot survive the cold. In contrast, diseases such as smallpox, measles, and influenza move directly from person to person. Consequently, they are not confined to particular climatic zones. Eventually, any population that is exposed will develop resistance to these airborne epidemic diseases.
Insect-borne tropical diseases cannot travel outside their own geographical hot zone. The only way people can become habituated to malaria or yellow fever is to migrate into the tropics and settle among the insects that carry these infections. For example, if yellow fever had been able to spread from Africa around Europe and the Middle East, the inhabitants of these colder regions would have built up resistance over several generations. Then when they entered Africa, they would have been resistant because of prior exposure.
Of course, African tropical diseases have spread, but only to the tropical zones of America and Asia. Such transported African diseases have continued to act as a biological force field to protect their carriers. In 1801, the black slaves in the French colony of Haiti revolted. Napoleon sent in experienced French troops who, other things being equal, should have easily suppressed the revolting slaves. Yellow fever, imported from Africa with the slaves, won the war by killing nearly 30,000 French troops. The slaves were mostly resistant to yellow fever because their African ancestors had adapted to it for many generations. Napoleon withdrew, and Haiti has been independent ever since.
Europe eventually conquered Africa because of superior military and medical technology. However, Europeans have never adapted biologically to the diseases of tropical Africa and must constantly take precautions such as antimalarial drugs and mosquito nets to preserve their health. Moreover, the European conquest of Africa has proven transient, with little permanent settlement, except in regions with temperate climates, such as South Africa. The inability of Europeans to live “naturally” in the tropics has hastened imperial withdrawal.
Is bigger really better?
The Persians tried several times to invade Greece. After Darius was defeated at the battle of Marathon in 490 B.C., his son Xerxes returned to Greece ten years later. Xerxes led the largest army the ancient world had ever seen, supposedly of 800,000 men, although it is hard to believe that these numbers were not wildly exaggerated. Of these, 300,000 rapidly succumbed to disease. The identity of the disease, or diseases, is not known. Plague and dysentery have both been suggested. Plague is usually a disease of settled communities, not of armies on the march. Dysentery seems more likely, although it mostly causes widespread debilitation with a sprinkling of fatalities, not death on a massive scale. In any case, the Athenians annihilated Xerxes’s navy—also oversized and badly organized—at the battle of Salamis in 480 B.C., and Xerxes quit his disastrous campaign and went home to Persia.
Despite Xerxes’s example, the idea that the way to win a war was by assembling the largest possible army of dirty, badly fed, poorly trained soldiers remained popular among ambitious leaders. The Crusades of medieval times (from 1096 to the early 1200s) are another example. Religious hatemonger Pope Urban II started the Crusades, supposedly to rescue the Holy Land from the Moslems. More likely, the real motive was to direct attention away from the corruption and incompetence of Vatican-dominated Europe. High points include the loss of 5,000 horses (out of 7,000) in an epidemic while the crusaders were besieging Antioch in 1098. Without their horses, the heavily armored crusader knights were helpless. Louis VII of France led some 500,000 men on the Second Crusade, and only a few thousand returned. Richard the Lionheart of England (1189–1199) left his country to wallow in economic insolvency while he went on the Third Crusade and failed to take Jerusalem. His massive army was reduced to a handful of survivors by malnutrition and infectious disease. The microorganisms were definitely on the side of the cleaner Moslems, with their smaller, better-trained armies.
Disease versus enemy action
Before about 1800, plenty of rough estimates show that infections killed vastly more soldiers than the opposing army. During the 1800s, more detailed records began to appear. In the Crimean War (1854–1856), the British lost ten times as many soldiers from dysentery and typhus as from Russian action. The mere fact that accurate numbers were recorded is an indication that at last the military was beginning to worry about the loss of manpower from disease. The squalor of the Crimean war inspired Florence Nightingale to push for reforms in hygiene, both in the armed forces and back home in England’s filthy cities.
By the Boer War (1899–1902), in which the British fought Dutch settlers for control of South Africa, the ratio had sunk to five deaths from disease to one from enemy action. The turning point was the Russo-Japanese War (1904–1906), in which the Japanese lost only one quarter as many men from disease as from enemy action. Over the next decade, the world’s advanced countries copied the Japanese: After scrubbing their recruits clean, they inoculated them against typhoid, tetanus, smallpox, and other infections.
In World War I, most armies stayed relatively free of disease. The major exceptions were the Serbs and Russians, whose outdated and ill-disciplined armies suffered massive losses from typhus fever. The only significant epidemic among the Western Allies in World War I was syphilis, and this caused trivial damage in comparison with losses to disease in earlier wars. Venereal diseases are a special case because they are aided in their spread by embarrassment and secrecy. (The Spanish Flu of 1918–1919 killed more humans than the military actions of World War I, yet this was a worldwide pandemic share
d by civilian and military alike, not a specifically military problem.) By World War II, antibiotics and insecticides had made their appearance, too. Soldiers and sailors#8212;and sometimes civilians in war zones or refugee camps—were dosed, disinfected, dusted, and deloused. In our modern era, infectious disease kills fewer soldiers than military action.
Since World War II, the major effect of infectious disease on the military of the industrial nations has been indirect. Providing ever more costly medical care to forestall every imaginable ailment has made armies more expensive. The result has been a decline in the advanced nations’ desires to intervene in the Third World, especially in the less hygienic parts. Thanks to rising health standards, the citizens of industrial nations have come to expect their full three-score years and ten. American conscripts in Vietnam had little wish to risk losing 50 to 60 years of life expectancy for little convincing purpose.
Typhus, warrior germ of the temperate zone
Which diseases were responsible for slaughtering the armies of Xerxes or the crusaders remains a mystery. As we approach more modern times, the identities of diseases that have overthrown armies start emerging from the mists of history. During the 1300s and 1400s, the Black Death killed soldier and civilian alike.
From 1494 to the early 1500s, syphilis caused major casualties among the military, but typhus soon emerged a far greater problem. In 1494, the French were forced to withdraw from Naples because of an outbreak of syphilis. In 1528, they were still fighting Spain for control of Italy and were forced to retreat from Naples again. This time the French lost 30,000 men to typhus. From the sixteenth century on, typhus became the major microbial player in the military arena.
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