The Victories Of The Vectors

Insects have carried disease onto the battlefield for more than two thousand years. For example, during the Peloponnesian War in 429 bce, flea-infested rats on Greek warships brought plague from Ethiopia and hastened the collapse of the Athenian state.1 The beneficiaries of this and other such fortuitously timed epidemics were apt to interpret outbreaks as divine interventions. The ancient Hittites and Babylonians were particularly explicit in this regard, paying homage to Irra, the archer-god who could fire arrows of disease into the enemy.

The Greeks had even deeper insights, believing that Apollo decimated enemies by using invisible plague-arrows and sending infestations of rodents.2 So while the rodent-disease association had been made, fleas remained as invisible arrows. In 396 bce, the citizens of Pachynus, Sicily, implored Apollo to loose his biological weapons on the approaching Carthaginians. Their prayers were answered when a pestilence—most likely bubonic plague—irrupted on the invaders' ships and the fleet turned back before reaching Sicily.3

Such events were relatively isolated, until civilization provided the ecological conditions that painted a target for Apollo's insectan arrows on the backs of soldiers. Several factors conspired to create an unprecedented opportunity for disease vectors. As the human population grew, the scale of armies increased commensurately. In the 18th and 19th centuries, encampments became like small cities with even less sanitation than their permanent counterparts.

With impotent medical interventions and miserably inadequate nutrition, the exhausted troops were sitting ducks for the insect vectors. Surviving on meager rations and drinking polluted water, the soldiers' defenses were pitifully weak against six-legged infiltrators and their microbial comrades. Factor in the lack of bathing and laundering, and the insect parasites were virtually assured of a rout. Moreover, as the devastation of war reached into urban centers overflowing with humans and waste, the beleaguered cities became epidemiological powder kegs.

If all of this were not enough, the modern era also ushered in transportation technologies that allowed armies to cross geographic barriers that had long kept people—along with their insect-borne diseases—isolated from one another. With shipbuilding and maritime navigation racing far ahead of medicine, vectors had a bilateral field day. European invaders of the New World brought with them new organisms—including infective microbes, blood-feeding insects, and adaptable rodents—and were greeted by a fusillade of unfamiliar pests, parasites, and pathogens. Hans Zinsser, author of the 1934 classic in the field of medical entomology, Rats, Lice and History, maintained that the famed battles of early modern warfare "are only the terminal operations engaged in by those remnants of the armies which have survived the camp epidemics."4

Napoleon Bonaparte has been called the greatest military mind of all time. He was a brilliant tactician, and perhaps no human opponent could consistently get the better of him. But six-legged enemies were another matter altogether. For every one of his soldiers killed on the battlefield, four succumbed to disease—and in most cases the illness was courtesy of a pathogen carried by an insect.

Napoleon's first lesson in the capacity of insects to alter the course of a military campaign came when the Ottoman Empire declared war on France in 1799.5 Napoleon anticipated that the Turks would attack Egypt, which the French had taken a decade earlier. Figuring that the best defense was a good offense, the French sailed to Syria and unloaded 13,000 troops looking to bring the war to the Turks on Napoleon's terms. As his army easily captured a series of coastal towns, it appeared that the plan to foil the impending Turkish offensive would succeed. However, a stunning reversal of fortune was waiting in Jaffa.

When the French stormed the city, the soldiers became crazed with blood-lust. Over the next three days, Napoleon's men ignored the enemy's attempts to surrender and bayoneted some 2,000 Turks. The slaughter culminated with Napoleon's ordering the execution of 3,000 prisoners. But the fleas of Jaffa would wreak revenge. Within two days of victory, 31 French soldiers were hospitalized with bubonic plague and 14 were dead. The doctors kept their diagnosis secret to avoid creating panic, and the commander visited the sick ward to reassure his troops. But Napoleon could not play nursemaid; he had a war to win (see Figure 5.1).

Figure 5.1. A romanticized recreation of Napoleon visiting his sickened troops in Jaffa, by Antoine-Jean Gros (1799). The French ruler ordered the painting to dispel rumors accusing him of having poisoned his sickest soldiers. Transmitted by fleas, an outbreak of bubonic plague cut short Napoleon's effort to defeat the Turks in Syria. Most of the 2,000 men that died in the campaign were victims of plague, with an incredible 92 percent mortality rate among those showing symptoms. (Art Resources)

Figure 5.1. A romanticized recreation of Napoleon visiting his sickened troops in Jaffa, by Antoine-Jean Gros (1799). The French ruler ordered the painting to dispel rumors accusing him of having poisoned his sickest soldiers. Transmitted by fleas, an outbreak of bubonic plague cut short Napoleon's effort to defeat the Turks in Syria. Most of the 2,000 men that died in the campaign were victims of plague, with an incredible 92 percent mortality rate among those showing symptoms. (Art Resources)

The French offensive moved northward, and the plague came along. Having been routed at Haifa, the Turks finally made a stand in Acre. Napoleon's army laid siege to the port city, but their cause was futile. The British navy gleefully supplied the Turkish troops with food and ammunition. For two bloody, feverish months, Napoleon's army relived the suffering of Janibeg's horde. When a last, desperate assault on the stronghold failed, Napoleon asserted that Acre was no longer of strategic value because plague had irrupted within the city. This excuse thinly disguised the real reason for his retreat. The French would soon lose a war of pathogenic attrition unless they could make it to safety.

Napoleon headed toward Egypt with his army continuing to wither. The sickened troops could not make much speed and Napoleon worried that the Turks would catch them and even the score. By the time they made it back to Jaffa, where Napoleon had executed his Turkish captives, the French commander saw no option but to issue a similar order—for his own men.

Napoleon directed that 50 of his sickest men be given an overdose of opium. The doctor protested, but the Turks were within hours of the city and Napoleon could not afford to slow the rest of his troops by burdening them with their dying comrades.

Three months later, Napoleon and the remnants of his army reached Cairo. Two thousand men had died in the expedition with many, perhaps most, succumbing to plague. Some historians maintain that disease was not decisive in the defeat, but it was surely a major factor in the physical and psychological condition of the French throughout the campaign. Napoleon's doctors reported a staggering 92 percent mortality rate among those showing symptoms. The onset of fever was tantamount to facing a firing squad, with the fleas of Jaffa delivering death at point blank range. But this was only an entomological skirmish compared to what the French would face 30 months later and 7,200 miles to the west.

Sans moustiques, les Etats-Unis pourraient être francophones—that is, "without mosquitoes, the United States might be French-speaking." In particular, without a strange convergence of African slavery, Haitian audacity, and French hegemony, American history could have been profoundly different.6 In 1801, François Dominique Toussaint L'Ouverture—the son of slave parents— declared himself Haiti's governor-general for life. There was only one small problem: France considered itself the owner of this Caribbean island.

L'Ouverture was no fool. After his pivotal role in the slave uprisings of the 1790s, he rapidly consolidated his power base. A savvy politician, L'Ouverture was a fair-weather ally of Spain and France, depending on who had something to offer. The French promoted him to the rank of general, and it was from this military perch that he named himself the island's ruler. Such insolence was too much for Napoleon. He had plans for an empire rooted in French Louisiana and extending far up the Mississippi River. So Napoleon sent his brother-in-law, General Victor-Emmanuel LeClerc, along with 20,000 troops to reclaim Haiti. As in the Syrian campaign, all went well at first.

The French landed in late January of 1802 and seized control of the island after a few short, bloody battles. Had LeClerc been a rapt student of entomological history, he might have predicted that insects would create military havoc in the Caribbean. In the 1650s, the English chose not to invade Cuba when they mistook fireflies along the shoreline for the torches of Spanish troops. And in 1761, termites clandestinely hollowed out the French stockades built to defend the Antilles. When the English gunfire reduced the wooden shells to sawdust, the British easily overran the crumbled bulwarks. In 1802, however, the insects were not so subtle.

Soon after LeClerc's initial victory, many of his soldiers became sick with a high fever. The first wave of 600 debilitated men doubled in a week. And those who had initially fallen ill began to develop horrible symptoms culminating in gruesome deaths. Yellow fever would make the French wish they'd left Haiti to its malcontent governor-general.

Yellow fever is caused by a virus that was imported to the New World from Africa via the slave trade.7 At first, native American mosquitoes circulated the pathogen among treetop monkeys. But it was not long before the virus was reunited with its African vector, which had a taste for humans. The yellow fever mosquito, Aedes aegypti, was a stowaway in water barrels on slave ships, and once it teamed up again with the pathogen, the deadly duo started making history.8

From 1693 to 1901, more than 100,000 people died from yellow fever in the United States. Epidemics ravaged the cities of the Gulf Coast and Atlantic seaboard, including New Orleans, Mobile, Charleston, Norfolk, Baltimore, New York, and Boston. Disease-carrying mosquitoes moved inland, triggering an outbreak in Philadelphia that killed 10 percent of the city's population in 1793. A yellow fever epidemic took at least 20,000 lives across more than a hundred towns in the southern United States in 1878.9 And theirs were not easy deaths.

The symptoms of yellow fever begin within a week of being bitten by an infected mosquito.10 The individual first experiences a high fever, debilitating headaches, and severe muscle pains. Often, there is a period during which the patient seems to have recovered for two or three days—and then the disease returns with a vengeance. The person's skin becomes jaundiced as the virus attacks the liver. The disease was nicknamed "Yellow Jack" by the British, in reference to the coloration of the skin and the yellow flag flown by ships with victims in quarantine. A bizarre, but not infrequent, symptom involves constant hiccupping so that even when the patient is lucid there is no rest or comfort. Splotches of blue and black appear on the body as vessels rupture. In many cases, the victim vomits what appear to be coffee grounds, but this is actually coagulated blood from internal hemorrhaging, which explains why the Mexicans referred to the disease as "el vomito." As blood continues to seep from damaged vessels and bleeding develops from every orifice, major organs begin to fail. Delirium gives way to coma, with death soon to follow.

Not all patients succumb to the disease. By controlling fever, preventing dehydration, and providing transfusions, today's physicians can save four of five victims, although convalescence may require months or years. On the other hand, without medical care, mortality can be staggering. The British saw a force of 27,000 men reduced to a mere 7,000 by "Black Vomit" on their failed expedition to capture Mexico and Peru in 1741.11 And in Haiti, LeClerc and his troops were well on their way to proving the old adage: those who fail to learn history are doomed to repeat it.

In April, the rains came to Haiti and the mosquitoes followed. Aedes aegypti is what entomologists call a "container breeder"—it lays its eggs in water-filled barrels, troughs, pots, and buckets that humans provide in abundance. There were evidently plenty of breeding sites, because by the end of the month one-third of the expeditionary force was dead. With the French losing 30 to 50 men per day, L'Ouverture saw an opportunity to negotiate the terms of a truce. But he underestimated the skullduggery of LeClerc, who invited the Haitian leader to dinner only to have him arrested and sent to France. Such dishonorable tactics enraged the locals, who resumed hostilities. Through the long, tropical summer, the French continued to suffer horribly. By October LeClerc was down to one-fifth of his initial force, and he finally succumbed to yellow fever himself.

Napoleon sent reinforcements, but for most of these men it would be a one-way trip. Along with fresh troops came a new commander, General Jean-Baptiste Donatien de Vimeur, Comte de Rochambeau. He was brutal, verging on genocidal, in his tactics, which included releasing 700 fighting mastiffs to shred the Haitians. But the mosquitoes of Haiti were far deadlier than the dogs of France. Rochambeau saw another 20,000 soldiers succumb to yellow fever in the year after their arrival. The French had no choice but to capitulate, returning to Europe with a scant 3,000 soldiers and leaving no fewer than 40,000 as mute testimony to the power of insect-borne disease.

Along with Rochambeau's retreat went any hope of France's controlling North America.12 While the French military was suffering defeat in Haiti, the French government was negotiating the sale of its interest in North America. In 1803, Napoleon sold his country's land in the Mississippi Valley to the fledgling United States for a mere $15 million, and a year later Haiti became the first independent nation in Latin America. If a tiny proto-nation could—with the help of insect vectors—repulse tens of thousands of Napoleon's men, then what could the largest nation on earth accomplish when it unwittingly allied with six-legged mercenaries to engage the Grande Armée of France a few years later?

In the early 19th century, Napoleon looked to the east and saw an opportunity and an obstacle. The opportunity was India, a British colony that Napoleon coveted. But to take this prize, he would need to move his army overland, as Admiral Nelson's fleet would pulverize him on the high seas. Consequently, the campaign would take him through Russia, a tenuous ally who would not tolerate a few hundred thousand French soldiers tromping across the countryside. So Napoleon found an excuse to invade. The Russians had been trading with England, thereby violating Napoleon's decrees prohibiting commerce with France's archenemy.

In late June 1812, the Grande Armée amassed for the invasion.13 Realizing that 450,000 men would require a tremendous amount of food, Napoleon hoped to stretch his army's supplies by prohibiting the soldiers from touching their rations while crossing Poland. Until they reached Russia, his troops would have to live off the land—and steal from the peasants. The troops met with no resistance from the villagers, who were woefully impoverished and, most important, terribly infested. Upon reaching the Niemen River marking the Polish-Russian border, the marauding soldiers found that they had not only acquired the peasants' stores but their annoying vermin as well. And compared to the devastation soon to be wrought by these six-legged time bombs, the Grande Armée's plundering of Poland would look like a diplomatic mission of mercy.

While spending two weeks in Vilna to rest and recover, Napoleon's men began to develop raging fevers and rashes on their chests and backs. Over the next few days, the debilitating fever persisted and the rash spread to cover a victim's body. After another week of severe headaches and muscle pains, a sick soldier was spared this torment by periods of stupor and delirium. But these respites meant that a patient's heart and brain were swelling with fluids, and death would come soon. If they had but known, perhaps the sick could have gleaned some perverse satisfaction in knowing that typhus was just as lethal to its vector.

We play host to three kinds of lice (order Phthiraptera): pubic or crab lice (Pthiruspubis), head lice, and body lice (aka "cooties").14 The latter two beasts are subspecies of Pediculus humanus, differentiated primarily by their preference for living on our scalps or in our clothing. Head lice lay their eggs, or nits, on the hair of their hosts, which give rise to both the next generation of insects and colorful expressions. We have louse eggs to thank when we accuse a person who focuses on minute issues of being a "nit picker" and when we assert that something is examined with a "fine-toothed comb" (a device used to extract the barely discernible nits). Body lice flourish in the warm, moist environment provided by undergarments. The insects crawl from the folds of cloth to grab a blood meal and then retreat to mate and lay eggs, with a female producing as many as 5,000 offspring in just three months. About the size of a grain of rice, these tiny insects don't wander far unless a body becomes inhospitably hot from fever or cold from death—as with a typhus infection.

The pathogen, Rickettsiaprowazekii, is a rickettsia, which can be thought of as a specialized bacterium that can reproduce only within a host's cells.15 Oddly enough, although the louse acquires the microbe by feeding on an infected human, the insect does not pass the pathogen via feeding. Rather, the rickettsiae multiply spectacularly in the louse's gut cells until they rupture and release enormous numbers of microbes into the doomed insect's feces. The unwitting human then acquires the fecal-borne pathogen through breaks in the skin caused by vigorous scratching (few conditions itch more than an infestation of lice) or across mucous membranes.

This was not the first time that typhus had altered the course of French military history. In the early 1500s, Charles V rose to power in large part owing to this insect-borne disease wiping out all but 4,000 of a 28,000-man French army. And in 1741, lice proved that they had no nationalistic leanings, annihilating a force of 30,000 Austrians who consequently turned Prague over to the French. But these outbreaks paled in comparison to the toll that louse-borne disease would take on Napoleon's army.

While the ever-retreating Russian army refused to engage Napoleon, the Polish lice were winning a war of attrition. One month into the campaign, the Grande Armée had lost 80,000 soldiers to disease, with dysentery adding intestinal misery to the typhus epidemic. With Moscow still nearly 300 miles to the east, Napoleon pushed onward. By the end of August, he had lost nearly half of his men, and a couple of weeks later his invasion force had deteriorated to 130,000 troops. And still, the Russians refused to fight.

In early September, Tsar Alexander I finally ordered his military to engage the enemy at Borodino, where the French killed 50,000 Russian troops in a one-day battle. Bolstered by this victory, Napoleon made a final thrust into the heart of Russia. When his troops entered Moscow a week later, they discovered that the Muscovites had burned three-fourths of the city and destroyed all of the food stores. The Russians refused to surrender and simply waited until the hungry, louse-ridden invaders had no choice but to retreat.

In mid-October, Napoleon's army was down to 95,000 exhausted men. Reaching Smolensk in early November, they were now brutalized by raging fevers within and bitter cold without. At times, the Grande Armée was losing 250 men per mile on the return to Vilna, where half a million of Napoleon's men had passed through in June. Just 7,000 able-bodied men along with 20,000 stragglers left the city. Typhus raged among the 25,000 who were left behind, and only 3,000 lived to continue their journey home the following year. Napoleon's army made it home in late December, with fewer than one in ten having survived the campaign.

In a matter of half a year, the Grande Armée had lost 400,000 men, with more than half dying from disease (primarily typhus) and many thousands more succumbing to hunger or cold because they were weakened by the louse's lethal microbe. The French would never fully regain their military might. It is ironic, and perhaps fitting, that Napoleon—one of history's shortest generals (standing just five-and-a-half feet)—was finally beaten by one of the animal kingdom's smallest creatures (stretching only a tenth of an inch).

Warfare had become a struggle against human opponents and insect-borne disease. And the Americans would soon affirm Zinsser's interpretation of military history: the glorious battles of the nation's bloodiest war were "the terminal operations engaged in by those remnants of the armies which have survived the camp epidemics."

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