The body louse had been from time immemorial the carrier of the fatal disease.

From The Illustrious Dead by Stephan Talty.  Page 269.

In January of 1909, in the small villages miles from the capital of Tunisia, men began to fall sick. The symptoms were fever, headache, lethargy, and spots on the trunk, legs, and arms. The relatives of the stricken men knew from experience that there was little to do but wait the disease out. Death would take those it wanted.

In the spring, the disease started to appear in the city itself. Men—it seemed mostly to be men, and young men especially— began turning up at local hospitals or were found prostrate in the “Moorish” cafés frequented by locals, as well as in the zaouias, the Sufi spiritual schools where people from the countryside traveled for instruction in mystic Islam. Men would wander into the local hospitals and collapse, their faces puffy and darkened, their eyes staring or manic, days from death. In April, the numbers rose steadily; in May, there was a sudden spike in cases. Doctors sent the overflow patients to a lazaret outside of the city, as their wards were overwhelmed. Some 4,000 Tunisians caught the disease, 836 in the capital. And 32.6 percent of them died.

Typhus was endemic in Tunisia. It had become a part of the natural cycle, as expected a part of the seasons as rain or the raising of crops. But 1909 was different for two reasons: Typhus had bloomed into a serious epidemic. And Charles Nicolle was waiting for it.

Nicolle was a French doctor who had come to Tunisia to head up the Pasteur Institute and make his name. He was a scientist to the marrow, a believer in the precise inductive reasoning that had led the master to his great contributions to germ theory that finally banished miasmism as a medical philosophy. Nicolle even admitted he wished to become the “next Pasteur.”

Sailing for the North African colony, Nicolle was in one way following in the footsteps of Napoleon; the Pasteurians saw themselves as benign imperialists, venturing to the corners of the earth to spread rational French science and culture by persuasion and not war. The “civilizing mission” that Napoleon had marched under, promising progress and liberty when in fact he most often brought tyranny, was the same banner that brought Nicolle to this outpost of the French Empire.

Nicolle began his pursuit of the disease’s cause only a year after arriving in Tunisia, when he and two colleagues planned a research trip to one of the small villages, Djouggar, about fifty miles outside the capital, that acted as incubators for the disease. But days before their departure, Nicolle began spitting up blood and was unable to make the journey (the illness, a lung ailment, turned out not to be serious). His collaborators, the doctor in charge of the village and his servant, set out for the outlying town. While there, both caught typhus, and when they returned, after days of agony, both died of the disease. Rickettsia had claimed two more of the countless pursuers it had killed without granting them a basic insight into its secrets. “Without this incident,” Nicolle later wrote, “my first contact with typhus would doubtlessly have been my last.”

Nicolle soon learned that most of the doctors in Tunisia eventually caught the disease, and one-third of them died of it. This was made even more disturbing by the fact that animals never seemed to succumb, so that one couldn’t study typhus safely in lab specimens or keep the pathogen alive between epidemics.  Humans alone seemed to carry the pathogen and die from it, and to get close to it one had to take the chance of catching it. Nicolle needed to figure out typhus’s modus operandi not only to make his name but also to have a fair chance of staying alive. And despite hundreds of years of study and millions of victims, the accumulated scientific knowledge of the disease’s cause was near zero. Humankind essentially knew nothing definitive about what caused the disease, how it spread, or how to stop it.

For three years, the expatriate doctor had been following the clues that typhus left in its annual cycle. It arrived in the rural districts outside Tunis in winter, then spread to the “doss-houses and the prisons” of the small villages and towns by early spring. From there it would reach into Tunis itself through the jails and the tightly packed neighborhoods populated by natives. By June or July it was gone. It favored a particular type of person: Many of the victims belonged to the underclass of the French colony— single men who worked as day laborers or farmhands, or begged in the streets for alms, barely able to live on the small coins dropped in their hands. Women and children were far less likely to come down with the disease. And curiously, one of the established facts about typhus’s spread, that it flourished in confined spaces, seemed exactly the opposite of what was happening in Tunisia. The disease spread across the country not in winter, when families stayed in their closely packed homes and villages, but in the spring, when people began to move and travel. Why?

And, if the pattern of infection was so consistent and followed a perennial route, why did the disease reach epidemic proportions in some years (such as 1906 and 1909) but not in others (1907 and 1908)? After looking at other factors that affected the poor— especially food supplies and weather—Nicolle and his collaborator, Ernest Conseil, realized that the most severe typhus years coincided with famines that sent unemployed single men flocking to the cities.

The local hospitals were known to be flash points, as so many of the doctors and staff who came in contact with typhus victims eventually died from the disease. That argued for person-to-person infection. But when Nicolle and Conseil looked more closely at the “the data, they realized that not everyone in the hospitals was catching the disease; even though typhus victims were mixed in with other patients, the other patients failed to fall ill with the fever. There was clearly a dividing line over which the pathogen didn’t cross. It was killing people in the receiving wards, but somehow it was stopped before reaching the upper floors.

Clearly, the microbe wasn’t spread by simple human-to-human contact. Nicolle began to suspect that the vector was an insect. Following the postulates developed by the pioneering researcher Robert Koch, he began injecting monkeys with blood from infected patients in 1906. The first trials failed, and Nicolle theorized that it was the fault of the test subjects: monkeys were too distant from their human cousins to have the same susceptibilities to disease. He sent for a chimpanzee, physiologically the creature closest to man. The chimp had to be imported from Marseille at the exorbitant cost of 550 francs. As Nicolle waited for the Pan troglodytes to reach Tunis, June arrived and the number of typhus cases began to fall off. The epidemic, as it did every summer, was fading; if the chimp didn’t arrive “soon, Nicolle would have no infected blood with which to inoculate it, and he would have to wait until the next plague swept Tunisia.

Finally, the chimp arrived in its crate and Nicolle quickly injected it with blood from an infected thirty-five-year-old Tunisian man. Now he watched and waited. At first, nothing happened. The chimpanzee stared back at the French scientist with its warm, placid brown eyes, revealing no signs of sickness. Nicolle went home and dropped off to sleep. When he returned in the morning, the chimp still regarded him with the same bored and perfectly healthy gaze. But twenty-four days after receiving the infected blood, his test subject began to display unmistakable signs of fever. The chimp was the first nonhuman vertebrate victim of Rickettsia ever observed.

Nicolle worked quickly. He took blood from the chimp and infected a macaque, a Chinese monkey. Nothing happened. For twelve days, Nicolle watched the macaque closely. On the thirteenth day, the monkey’s eyes began drooping and a thermometer revealed that he was running a high fever. Nicolle had isolated the microbe. Now he had to locate the vector.

The doctor had narrowed his search for the typhus carrier to one insect: the common body louse. In Tunisia, especially in the rural districts, lice were the only parasites universally found on the body and clothing of “the wretches” who spread the disease. Nicolle placed a number of healthy lice on the fur of the sick Chinese monkey. After giving them time to feed on their host, he transferred the lice to a healthy monkey. Within days, it had fallen ill with typhus. Nicolle had proved that the body louse had been from time immemorial the carrier of the fatal disease.