Colorado tick fever

"July 25th, Thursday 1805 a fine morning we proceeded a few miles to the three forks of the Missouri."1

So wrote William Clark, knowing well that the Corps of Discovery had reached a critical point in its journey west.

Three Forks: confluence of the Madison, Gallatin, and Jefferson rivers. Located in west-central Montana, these streams join in a single valley to form the headwaters of the Missouri River. In summer 1805, Clark and a small Corps of Discovery lead party had finally reached the "shining mountains" and the three forks of the uncharted upper Missouri, the last point on the geographic sketch the Mandan and Hidatsa Indians had given them the previous winter at Fort Mandan. Here they expected to find Sacagawea's people, the Shoshones, who they hoped would provide horses for the mountain passage to the Columbia drainage. Signs of native people were abundant-old encampments, a bow, human tracks, a horse, recent grass fires-and Sacagawea recognized the landscape, which seemed to augur a rendezvous with the Shoshones. To the exhausted members of the expedition, the Three Forks also signified the end to the arduous trek up the Missouri. As Captain Meriwether Lewis put it, this was perhaps "an essential point in the geography of this western part of the Continent."2 The long-sought overland portage to the Columbia River that President Thomas Jefferson envisioned could not be too far distant.

Despite the promise of the Three Forks, there was considerable apprehension, and Captain Clark, who had been filled with expectation, was disappointed. Neither the source of the Missouri River nor the Shoshones had been found. Summer i8o,5 was passing, and time was running short if the expedition was to reach the Pacific Ocean before winter. Arriving two days later, Lewis, like Clark, was anxious to hasten upstream. But Clark was so ill the entire expedition had to halt, and the delay was exasperating. They might just as well have named the three forks: the Anticipation, the Anxiety, and the Affliction.

Until then, illness had delayed the expedition only briefly. To be sure, Sergeant Charles Floyd had died suddenly the previous summer along the banks of the lower Missouri River, and in June i8o5 Sacagawea had fallen very ill for about ten days. But never had illness so incapacitated one of the corps' captains. For four days at Three Forks, Clark was prostate with weakness, fever, chills, and muscle pains. At a time when the pinnacle of the summer's journey lay just ahead, Lewis was obliged to lay over to await his partner's recovery.

Clark's illness has not been interpreted adequately. Despite an abundant literature and increasing interest in the Lewis and Clark Expedition, examination of its medical facets is limited to one standard text and a few papers.3 None of these considers Clark's "Three Forks Fever" in any depth, and some sources dismiss its significance entirely.4

At the turn of this century, scholars of the expedition attributed Clark's illness to "wading it cold water when over heated" and "drinking cold spring water."5 More recent writers have concluded that his illness was

an "intestinal problem," or that it had been caused by excessive physical activity, constipation, overheating, or infection from foot bruises and punctures of prickly pear spines.6 All such diagnoses fail to account for the severity of the symptoms, the timing of Clark's fever, the chronology of notations from expedition journals, and the other infirmities expedition members experienced.

Illness, injury, and exhaustion were frequent companions for the corps' journey, although serious medical problems, with the exception of Sergeant Floyd's death a year earlier, had been minimized by youth, vigor, and good fortune. Floyd, a young sergeant, had died twenty-four to thirty-six hours after the onset of acute abdominal pain, most likely from appendicitis. Illnesses marked by abdominal pain and diarrhea accompanied the men on the entire journey. Just a month prior to Clark's illness at Three Forks, Lewis had experienced a self limited (spontaneously cured) episode of diarrhea, fever, and severe abdominal pain while exploring the Marias River. Simultaneously, Sacagawea suffered a ten-day bout of fever, delirium, and pelvic pain from which she recovered.

As the ranking officers of what was a military expedition, Captains Lewis and Clark made all daily decisions and maintained discipline, and they were responsible for the health and well-being of the men. Military officers of the early i8oos were expected to provide basic first aid and medical care for their troops. President Jefferson, who held contemporary medical doctors in low regard, entrusted the care of the Corps of Discovery's men to the captains.7 With basic knowledge of common treatments, first aid techniques, and a tincture of ingenuity, Lewis and Clark fulfilled the role of expedition physicians as well as trained medical doctors of the early nineteenth century might be expected to do.

Jefferson, Lewis's mentor, was well read in medicine and botany as they applied to medical practice, and Lewis's years as Jefferson's personal secretary had provided him a grounding in medical knowledge. As expedition captain, Lewis often used herbal remedies for illnesses, including his own. Some of these he probably learned as a youth from his mother Lucy Marks, who was a "yarb" or herb doctor.8 It is only logical that Lewis would have kept some of her simples (herbal remedies) in mind when treating himself and his men, but Lewis had also received training from the most respected physicians and scientists of the day. Realizing the need to optimize the expedition's scientific value, Jefferson had sent Lewis to Philadelphia shortly after appointing him expedition leader. There, he received a personal tutorial from some of America's most influential men of science-the members of the American Philosophical Society. In letters of introduction to his scientific colleagues, Jefferson assured them that Lewis was a perceptive student of nature and sciences, possessing, as he said, "a great mass of accurate observation on all the subjects of nature which present themselves."9

While in Philadelphia Lewis called on Dr. Benjamin Rush, the country's leading physician, who Jefferson had asked to "prepare some notes of such particulars as may occur in his [Lewis's] journey & which you think should draw his attention & enquiry."10 Rush, a zealous proponent of "depleting therapies"bleeding, purging, and induced vomiting-probably recommended his own heroic remedies to Lewis. As army officers, Lewis and Clark were likely familiar with and adept at such treatments. Physicians of the day believed that purging the body of "morbid elements" and "inflammatory conditions of the blood" restored health. Dr. Rush in particular did not believe in letting nature resolve illness. Although the particulars of Rush's discussions with Lewis are not known, Rush assured Jefferson that he had provided Lewis with a standard list of rules for preserving the health of the troops.11

To satisfy his own anthropological interests in native American medicine, Rush also gave Lewis a list of questions relating to physical history, medicine, morals, and religions of the Indians living on the upper Missouri.12 Such investigations interested Jefferson as well. In his detailed letter of instructions to Lewis dated June 20, 1803, the president stressed obtaining knowledge of the native peoples the expedition would encounter and becoming acquainted with "the diseases prevalent among them, & the remedies they use." Anticipating the scourge of smallpox epidemics, Jefferson gave kinepox (cowpox) vaccine to Lewis to use wherever the corps wintered.13

Dr. Rush also influenced Lewis's purchase of medical provisions for the captains' medicine chest (see table).14 These stocks reflect the problems Rush and Lewis expected the expedition to encounter, including various gastrointestinal disturbances, ague (malaria) and other fevers, eye disorders, sexually transmitted diseases, and various sorts of trauma.15 In addition to numerous other laxatives, Rush specified six hundred of his own "bilious pills." Known as "thunderbolts," these pills were a powerful mixture of drastic laxatives, jalap and calomel.16 Lewis left Philadelphia with a therapeutic arsenal, an array of purgatives and emetics, and a set of lancets to incise veins.

In addition, Lewis spent time with Dr. Benjamin Barton of the University of Pennsylvania, a renowned physician and naturalist. Barton expanded Lewis's scientific grounding in botanical skills and probably enhanced his ability to supplement his medicine stores with natural herbal treatments. Barton's Elements of Botany (1803), the first American textbook of botany, served as Lewis's definitive reference on the voyage.17

Fatigue, strain, injuries, and physical adversities presented the greatest threats to the Corps of Discovery members' health. In addition to these, Lewis wrote on July 24, 1805, while camped about seven miles north of present-day Tosten, Montana, that "a trio of pests still invade and obstruct us on all occasions, these are the Musquetoes eye gnats and prickly pears."18

Prickly pear cacti had been a torment during the difficult portage around the Great Falls of the Missouri. Their spines impaled themselves in the men's feet, piercing even double-soled moccasins, and caused painful sores. By the light of the evening fire on July tg, Clark extracted seventeen prickly pear thorns from his own feet.19 Tramping over sharp stones and needle grass added to the trauma. Like prickly pear thorns, needle grass penetrated moccasins and leather leggings and punctured the skin. Even Lewis's Newfoundland dog, Seaman, suffered from needle grass barbs.

By mid-July, despite nearly daily references to sore feet and the corps' general exhaustion, Clark determined to push upriver and take the lead overland to find the Shoshones. As Lewis wrote on July 22, altho' Capt C. was much fatiegued his feet yet blistered and soar he insisted on pursuing his rout in the morning nor weold he consent willingly to my releiving him at that time by taking a tour of the same kind. finding him anxious I readily consented to remain with the canoes: he ordered Frazier and Jo. & Reubein Filds to hold themselves in readiness to acompany him in the morning. Sharbono was anxious to accompany him and was accordingly permitted.20

Clark and the four men arrived at the three forks of the Missouri on the morning ofjuly 25. By evening they had established camp near the mouth of the Philosophy River (present-day Willow Creek), having traveled twenty-five miles that day. Lewis noted in his journal that Clark had arrived at camp that day "much fatigued, his feet blistered and wounded with prickly pear thorns." Lewis did not comment on Clark's feeling otherwise ill on July 25.21

When Clark arose the next day, he hoped to explore the environs and perhaps find the Shoshones, for evidence indicated the recent presence of natives. As the first Euramerican to see and write about the three forks of the Missouri, he anticipated a day of discovery. By nightfall, however, Clark had succumbed to high fever and an illness that would persist four more days, forcing the party to lay over.

Toussaint Charbonneau, with sore ankles, and Joseph Fields, with painful feet, were left at camp to rest while Clark and the two other men, Robert Frazer and Reubin Fields, , set out on the morning of July 26 for a survey from a mountaintop vantage point twelve miles to the west. An exhausting climb brought them to the summit by 11 A.M. There they overlooked the river and valleys upstream but found no evidence of Indians. Following an old path back to the river, they passed by a cold spring. The day had grown hot, and the thirsty men drank liberally of very cold water. In the belief that drinking cold water when overheated was harmful, Clark took the precaution of first cooling himself by wetting his feet, hands, and face with the water. Despite these safeguards, Clark "soon felt the effects of the water" and began feeling "unwell."22 Upon returning to camp, they found Joseph Fields had freshly killed a fawn, and Frazer and Reubin Fields, apparently feeling no ill effects from the cold water, ate heartily of the venison. Clark had no appetite, however, and complaining of fatigue, again noted sore feet from blisters and prickly pear thorn punctures.

His indisposition notwithstanding, Clark had the men move camp upstream. Crossing the waist-deep Jefferson River, Charbonneau, who could not swim, was nearly swept away by the rapid current. Despite his weakened state, Clark rescued the Frenchman from drowning. Adding to the excitement that evening, the men killed two grizzly bears. Because Clark planned next to cross eastward to examine the middle fork of the Missouri, they made camp three miles above the mouth of the Philosophy River. "I felt myself verry unwell," Clark noted, "& took up camp."23

Clark's illness intensified. He suffered throughout the night from chills and high fever, accompanied by bone and muscle aches. Despite increasingly severe symptoms, Clark and his men set out again on the morning of July 27 to rendezvous with Lewis and the rest of the party. Watching for Indian signs, they came to the middle fork (the Madison River) and rested an hour. Proceeding down the middle fork they arrived at the junction of the three forks at 3 P.M. and rejoined Lewis's party, which had arrived just an hour earlier. Updating Lewis on the previous three days' findings, Clark gave an account of his illness to his cocaptain. Lewis's detailed documentation of the illness in his own journals underscored the gravity with which he regarded Clark's illness.

The men of Lewis's party were exhausted from their incessant upstream exertion, but arrival at the three forks evoked great anticipation, though Lewis harbored anxieties and doubts about the corps' ultimate success. They had not found the Shoshones, whom they expected to meet in the vicinity, and game was growing scarce. Rather than push ahead, Lewis, because of Clark's illness, rested the men and tended to Clark, performed celestial observations to fix their position, and considered the trip ahead. To Lewis, who had attended the illnesses of many of his men and Sacagawea, fell the responsibility for restoring his friend's health.24 Until July 30, the Missouri's Three Forks became Clark's camp hospital (see map.

Lewis learned that Clark's bowels had not moved for several days and that he felt "somewhat bilious." Biliousness, in the vernacular of the eighteenth and early nineteenth centuries, was a catchall term that referred to symptoms thought to arise from an excessive secretion of bile or the accumulation of impure fermenting biliary substances. It was, in fact, a word for symptoms that included constipation, abdominal fullness, gassiness, and/or nausea, which could be accompanied by fever. Recovery required prompt purging.

In his medical armamentarium, Lewis had at his disposal some i,3oo doses of at least six different laxatives. His prescription for Clark's febrile illness was "a doze of Rushes pills." The patient followed the advice to rest and bathe his feet in warm water but determined himself the dose of the prescribed cathartic. Lewis recorded, "I prevailed on him to take a doze of Rushes pills, which I had always found sovereign in such cases," but it was Clark, still very sick and feverish, who recorded that he took five of Rush's pills.25 A single pill was powerful; this was a massive dose.

Lewis's approach was typical of early-nineteenthcentury medical practice. His mother the herb doctor probably taught him to open the bowels for any cause, and Dr. Rush likely influenced Lewis's therapeutic attack on "bilious fevers." Rush had given Lewis a list of rules for preserving health, which included prescription of purgatives. Rush believed that both lack of appetite and constipation heralded diseases that could be obviated by one or more of the purging pills.26

Had Clark's care been up to the doctor, Rush certainly would have employed his best lancet. Rush's strategy with serious fevers was to purge with powerful doses of calomel and jalap, followed by bleeding until the patient fainted. When the patient recovered consciousness, Rush would examine the pulse and bleed the patient again if necessary. In the case of Clark's Three Forks fever, however, neither Clark nor Lewis recorded the use of bleeding in his journal. By failing to use the lancet on Clark, Lewis settled on a less aggressive treatment with his friend than he consistently used with other members of the party.27

As dawn broke on July 28, Captain Clark remained ill. High fever and the aftermath of the five "thunderbolts" had created misery for him all night long. Lewis commented that the medicine had "operated," which undoubtedly added to Clark's weakened state. As morning progressed, however, Clark reported feeling somewhat better. The daytime temperature reached ninety degrees, and the feverish Clark was moved from the stifling leather lodge to a more comfortable shaded bower the crew made for him.

Despite Clark's being ill, the expedition was not idle. While members of the party hunted or explored the east fork, the captains conferred and agreed to name the three forks of the Missouri River in honor of Secretary of the Treasury Albert Gallatin, Secretary of State James Madison, and President Jefferson. As they nursed Clark back to health, the expedition's members also got much needed rest, repaired their clothing, explored the area, and replenished their food supply before the journey's final leg beyond the Missouri headwaters. For his part, Sergeant Gass made two journal entries on July 28 relating to Clark's illness. In the first, he noted, "Capt. Clarke still continued unwell"; but in the second, presumably written later in the day, Gass observed, "Capt. Clarke is getting better."28

Clark improved on July 29, the fourth day of his illness, reporting: "I feel my Self somewhat better to day." Lewis found him free of fever but still weak.29 Clark complained of soreness in all of his limbs, for which Lewis administered a dose of Peruvian barks. Containing quinine and other alkaloids, Peruvian barks, or cinchona, the "aspirin" of their time, exerted an antipyretic effect and thus relieved Clark of achiness and fever. With the fever abating, Clark was able to eat a meal of fresh venison for the first time in several days.

Anxious to resume their final push to the Jefferson River headwaters, Lewis was pleased to find his friend much improved by July 30. Reloading their canoes, they ascended the Jefferson River, each captain with a portion of the expedition party. Clark, in fact, recorded that one of his men, who had recurrent shoulder dislocations, had strained his shoulder again and that two other men had "turners" or skin abscesses. But he made no references to his own symptoms that day. The following day, July 31, a rested, healthier crew experienced slow upstream travel through difficult shoals and rapids. On August 1, Lewis with three men took the lead overland in quest of the Shoshones. Delay at the Three Forks spurred his haste to find the natives, whom he believed to be the key to passage to the Columbia drainage. By afternoon, exhausted from lack of water after a hot, steep, eleven-mile trek over a mountain range, Lewis, too, reported feeling ill, but his weakness was exacerbated by self medication. Having experienced a mild diarrheal illness for several days, he had attempted to cure himself of this ailment that morning with a dose of Glauber's salts (sodium sulfate, similar to Epsom's salt), a laxative. Lewis and many of the men frequently experienced diarrhea. Their standard remedy was gentle purging. Giardiasis or bacterial dysentery from spoiled meat may have caused the recurring bouts of diarrhea.

August 1 was Clark's thirty-fifth birthday. Making no comment about illness, he seemed to have recovered, and even provided lunch for his party that day by shooting a mountain sheep. Recovery from the Three Forks fever did not end his health problems that summer, however, for he would soon suffer another malady.

The following day, August 2, Lewis complained of an excessively cold night and an intensely hot sunny day on his overland trek.30 Clark and his men, meanwhile, struggled up the fast-running, torturous Jefferson River. That evening at camp, Clark discovered a painful swelling over the inner bone of an ankle, attributing this ailment to a poisonous insect bite or tumor (abscess).31 While walking that morning, he had observed several rattlesnakes, but he had not been bitten. Despite many close encounters with the vipers, the corps had recorded no snake bites since the previous summer.32

Clark's heavily laden stream-bound expedition traveled more slowly than Lewis's small advance party did afoot. Nonetheless, Clark was encouraged to find a fresh human track while walking along the river, from it inferring the proximity of natives. His walks overland ended on August 4, however, when the swelling abscess over his ankle became extremely painful. His men, suffering and weakened too from walking and wading over rocks and being in cold water from dawn to dusk, complained of swollen painful feet, which slowed upstream progress.

On the evening of August 5 Clark developed a slight fever and reported that his foot was "verry painful."33 Hearing of this, Lewis concluded that the ankle abscess had not matured enough to rupture spontaneously. The next day, Clark reported that his ankle was worse.

Camping downstream from "the beaver's head" on August 8, Sacagawea informed the captains that this landmark indicated her people's homeland was near. That same day, Lewis related that Clark's ankle abscess spontaneously drained a large amount of pus but remained inflamed, swollen, and painful.

The next day Lewis walked ahead with three men to find the Shoshones and horses for portage. Clark asserted that he should have carried out this mission, but in what would be the last journal entry relating to his health for this part of the expedition, he said he could not have endured the trek because of"the rageing fury of a tumor in my anckle musle."34 Afterward, the skin infection apparently healed and caused no further problems.

Previous authors have asserted that it was Clark's illness at the Three Forks that caused this ankle abscess, but did other factors such as excessive fatigue, constipation, or drinking cold spring water cause that severe illness? The answer to these propositions is no.

Both Lewis and Clark were astute observers, and in the case of Clark's Three Forks fever both wrote clear descriptions of the illness's nature, symptoms, and treatment. Though Clark described painful bruises and blisters on his feet, most of the men and Sacagawea too suffered from the same trauma during this part of the journey. Skin abscesses from skin abrasions, puncture wounds, and cuts were common.

The natural course of the skin abscess over Clark's ankle was typical. The flesh over the ankle became painful, he developed fever, and the abscess progressively enlarged as pus developed until it spontaneously ruptured and drained. Pain in an infected foot serious enough to cause four days of toxic illness would not have been overlooked in either captain's journal had it begun during those days at the Three Forks camp hospital. In fact, both men reported Clark's foot infection as a new event on August 2. Moreover, it is difficult to link Clark's Three Forks fever and the subsequent skin abscess. The source of an infection as serious as Clark experienced at Three Forks would not herald itself as an abscess eight days after the onset and three days after apparent recovery.

Other factors can also be ruled out. Other than the constipation and bilious complaints of July 27, neither man made other references to abdominal pain or intestinal problems after Dr. Rush's pills had "operated." Therefore, it is unlikely that an intra-abdominal or bowel infection played any role in Clark's illness. Furthermore, constipation does not cause fever, chills, and muscle aches, nor do excessive fatigue or drinking cold water. Given the prominent manifestations of Clark's Three Forks fever, we should perhaps consider an infectious etiology, but what would have caused such an infection?

To begin with, we should consider common illnesses of the early nineteenth century and what the corps was exposed to on its voyage, but it should be remembered that illnesses, particularly fevers, were not analyzed diagnostically or differentiated in the early nineteenth century. Benjamin Rush in particular dismissed any such categorization. "The essential principles of medicine are very few. They are moreover plain," he wrote. "The remote causes of diseases all unite in producing but one effect, that is irritation and morbid excitement, and of course are incapable of division."35

Dr. Rush's pronouncements notwithstanding, subsequent observers have suggested that malaria caused Clark's illness. Although not characterized until the end of the nineteenth century, what we now call malaria was very common along the eastern seaboard at the time of the expedition.36 Malarial fevers were classified together with most other causes of fever. Synonyms included ague, intermittent fever, intermittens, bilious fever, and autumnal fever. Mosquito-borne malaria was endemic in the Mississippi, lower Missouri, and Ohio River valleys, but the journals describe neither Clark nor any other corps member as having a relapsing illness of chills, fever, aching, and headache, which suggest chronic malaria.

Indeed, traveling the lower Ohio River in fall 1803, Lewis knew of "fever and ague and bilious fevers" in that region.37 Describing his own experience with such an illness in November 1803, he wrote: "I was seized with a violent ague which continued about four hours and as usual was suceeded by feever which however fortunately abated in some measure by sunrise the next morning." He medicated himself with the all-purpose "doze of Rushes pills which operated extremely well."38

Although he used the term ague, true malaria cannot necessarily be inferred because ague included any number of short-lived illnesses with chills and fever. In the early i8oos such illnesses were considered a single condition caused by "irritation and morbid excitement" of blood vessels to which standard depleting treatments were applied.39 In the case of his episode of "ague," Lewis demonstrated his preference for the "sovereign" therapy of Rush's powerful laxatives, repeating the same treatment two years later when Clark fell ill with a similar fever.40 By purging the "morbid elements" with Rush's pills, Lewis was in accordance with contemporary medical standards.

Clark actually suffered few infirmities during the Missouri River expedition; his Three Forks fever was an exception. The journals contain repeated references to one or more of the party being ill or injured, and the frequency of Clark's problems seems no different than that of the other men, although he described himself as ill on a few specific occasions. During the early months of expedition, the pre-Missouri River days, however, Clark was often ailing. In a letter to his brother, Jonathan, dated December 16, 1803, Clark reported two illnesses. The first had begun just a few days after Clark joined Lewis on the journey down the Ohio River that October. He described having been taken "Violent ill by a Contraction of the muskelur sistem." He recovered after several days, apparently receiving medical attention from Lewis. Two weeks later, he was struck with another illness that lasted eleven days. "I was again attacked with a violent Pain in the Sumock & bowels," he wrote, "with great Obstruction in those parts."41 Relief was not effected until the two men reached Kaskaskia (in present-day Illinois), where Clark procured some "Allow" (aloe), another natural purgative.42

Again, in January and February i8o4, while organizing and training the men of the expedition at Camp DuBois, located at the mouth of the Missouri River, Clark made several references to feeling "unwell" and treating himself with a "fessic" (laxative) and walnut pills, but there was no mention of specific symptoms to suggest a serious illness. The only clue to the nature of this lingering but self limited illness is found in another letter to his brother Jonathan, dated February 25, 1804: "I was at that time so unwell that I could not [write], my health at this time is Somewhat betterthoh not entirely Recovered from the Indisposition which attacked me in assending the river," Clark wrote. "I thought at one time I had entirely recovered, but haveing frequint returns of the disorder I am induced to believe that time and attention alone will destroy the effects [of] it." The only other complaints recorded in his journals prior to the Three Forks illness came in October and November 1804 when he remarked occasionally about "rheumatism on my neck," which Lewis treated with a hot stone wrapped in flannel.43

While at Fort Mandan the following winter, the sexual capers of the expedition's men with Mandan and Hidatsa women necessitated the captains administering ongoing treatments with mercurial salts for venereal diseases, particularly syphilis. Lewis and Clark were either celibate or discreet in their journal notekeeping, for they never revealed any such experiences or acquired infections themselves. Regardless, after a six- to eight-month latency, neither syphilis nor gonorrhea would present itself in such a manner as Clark's Three Forks fever.

Another possibility is that Clark contracted tick fever, a zoonotic infection. A zoonotic disease is a human illness caused by an organism usually resident in a nonhuman animal and communicated through bites, blood contamination, or a variety of biting arthropod intermediaries-especially ticks, mosquitos, and flies. Most zoonotic diseases are related to geographic or seasonal factors and spread by chance encounters with animal or arthropod vectors. Any one of several zoonotic infections could have caused Clark's illness. Tick-borne diseases, which cause symptoms similar tc those Clark suffered, include tularemia, Rocky Mountain spotted fever, ehrlichiosis, Q fever, and Colorad( tick fever.44

Clark had not described a problem with ticks or tick bites since the previous summer, but the Corps of Discovery was in wood-tick territory in July i8o5. Commonly, individuals afflicted with tick-borne illnesses fail to notice a tick bite. Being in an environment where ticks aboundriver valleys, growths of sagebrush, as Clark wasputs anyone at risk for acquiring these diseases.

Tularemia is an intriguing possibility for Clark's illness. Although usually acquired by a tick bite, inoculation of cut or scratched skin with bacteria while preparing infected rabbits or other mammals can lead to several forms of this disease. In the ulceroglandular form of tularemia, the site of the bite or cut becomes red and swollen and subsequently ulcerates. Fever and chills follow. If one tries to use this clinical picture of tularemia to tie Clark's Three Forks fever to the subsequent abscess over his ankle, however, it is apparent that Clark's illness had the reverse sequence of ulceroglandular tularemia. A typhoidal form of tularemia can have generalized and severe symptoms, including fever, chills, headache, muscle pain, and abdominal pains, but it produces prolonged debility if the untreated patient survives, which was not apparent with Clark's brief illness.

Rocky Mountain spotted fever (RMSF) is a disease caused by a rickettsial organism that circulates in nature in a complex cycle between ticks and small mammals. Humans are incidental hosts via tick bites. Although the early manifestations of RMSF are similar to Clark's symptoms, a widespread rash is usually prominent. Being good observers, Lewis and Clark would surely have noted a prominent skin rash. In an age before antibiotics, the disease was usually fatal.45

Ehrlichiosis, another rickettsial disease, has epidemiologic and clinical features similar to Rocky Mountain spotted fever, but a rash is less common. Most patients recover uneventfully but only after a prolonged period, much longer than the five days it took Clark to recover.

Q fever, also caused by a rickettsial organism, has sheep as its primary reservoir, and tick-borne transmission to humans is considered a rare occurrence. It can induce mild influenza-like symptoms and usually spontaneously resolves over weeks rather than days. Clark's only contact with sheep on the Three Forks leg of the journey occurred after he had recovered-on his birthday, August 1, when he shot a mountain sheep.

The disease that may best explain Clark's Three Forks fever is Colorado tick fever (CTF), a viral infection transmitted by the wood tick (Dermacentor andersoni). Both the wood tick and the CTF virus are found throughout the Rocky Mountains. Virus-infected ticks feed on chipmunks and ground squirrels in nymphal form and on larger mammats in adult form with humans being incidental hosts.46 Peak occurrences of CTF coincide with peak tick activity in the Rocky Mountain region, generally April to July. After an incubation period of three to five days, the infected individual experiences the abrupt onset of chills, muscle aches, fever, weakness, headache, and occasionally abdominal pain. The illness lasts from several days to a week or more. It resolves spontaneously but is often followed by lassitude and weakness.47

In July 1805, the Corps of Discovery was passing through ideal habitat for endemically tick-infected mammalian hosts-herbs and grasses covered with sagebrush, juniper, and pine overstory. Today CTF is commonly seen in southwestern Montana and is probably the region's most common arthropod-transmitted illness. Between 1981 and 1995, for example, half of the 168 CTF cases reported in Montana came from southwestern Montana counties (see map).48 Many people with this illness recover without seeking medical attention, some physicians may not recognize it, and physicians familiar with the disease may not report it. Thus, these numbers probably underrepresent the frequency of CTF in Montana. Given the clinical and epidemiologic picture, anyone presenting with manifestations of Clark's illness today would be suspected of having CTF.

Early settlers in the Rocky Mountain West and early travelers through this region became familiar with fevers that seemed particular to the western mountains. As great numbers of emigrants traveled through the Rockies in the mid to late nineteenth century, many of them experienced unexplained fevers in spring and summer months. They began to recognize a self limited fever accompanied by chills, headache, and muscle aches. Although these fevers likely included a variety of zoonotic infections, "mountain fever" became a catchall term for such febrile illnesses. Overland travelers often provided graphic descriptions, as did William McBride, an i85o emigrant:

At dawn this morning E. W. Summy and Lewis Mitchell applied to me for medications. They were severely and suddenly attacked last night after partaking of a hearty supper. Their disease is what the Mormons have termed mountain fever, being a disease particular to this region. Many patients complain of a most violent pain in the head and eyes with dimness of vision, pain in the back and limbs, great lassitude, alternations of chills and fever, nausea and vomiting, constipation. Such are the most prominent symptoms. The pain from this disease is very great! I prescribed for them and this evening they are some easier. I saw a company of nine men today which have been compelled to lay at Green River a week, five of their men having the mountain fever at one time-it is very common at the river. The disease cannot be said to be very dangerous, but it is severe.49

Note the similarities between Lewis's description of Clark's Three Forks fever and McBride's chronicle of "mountain fever."

Physicians in the late 18oos began characterizing various mountain fevers with and without rash. After a tick vector was identified, the disease with rash was named Spotted Fever of the Rocky Mountains and the fever without rash was called American Mountain Tick-fever.50 With publication in 1940 of a clinical description of a number of patients from Colorado ill with this disease, the malady became known as Colorado tick fever. The epidemiologic factors coupled with the clinical description of symptoms in the records of Lewis and Clark provide a picture of Clark's Three Forks illness as remarkably similar to modern-day Colorado tick fever.

Time and again Lewis affirmed Jefferson's wisdom in making him expedition leader. Jefferson's charge to Lewis to document his observations in the fields of geography, navigation, ethnology, natural history, and geology was amply fulfilled. Always keen observers and diligent writers, Captains Lewis and Clark added new scientific knowledge in all these realms. What has gone underappreciated is their addition of a new disease entity to the field of medicine. However unwittingly, they recorded in summer 1805 the first clinical description of a mountain fever in the Rockies, and Clark's Three Forks fever will likely stand as the first clinical description of Colorado tick fever.

Whether it was Lewis or Clark who treated the afflictions or injuries of the men, Sacagawea, her baby, or the natives who later in the expedition eagerly sought their medical care, the captain-physicians generously dispensed their medical stores, their concern, and their attention. Clark's Three Forks fever is a unique chapter in this epic story. It illuminates the precarious conditions of health and the resourceful practice of medicine in what to the captains was a wilderness. Clark's illness was severe but self limited. Had he become infected with any of the other causative organisms of a disabling or fatal "mountain fever," Captain Lewis might not have been able to save him.

The role of the expedition's principal physician shifted from Lewis to Clark in September after they reached the Pacific drainage. Clark then became the primary captain-physician and the "favorite physician" among the natives they visited. He treated his patients with intuitive skill and compassion. Was it Lewis's melancholia that thrust Clark into this role, or could having lain so ill at Three Forks have catalyzed his innate medical proficiency? We may never know, but in evolving from patient to "favorite physician," Clark's experiences surely show that a transformation occurred after the Three Forks.

RONALD V. LOGE, a Dillon, Montana, internist, is a graduate of the University of Montana (B.S., 1971, and M.S., 1972) and the University of Oklahoma (M.D., 1976). He is a member of the Lewis and Clark Trail Heritage Foundation. He has written previously about medicine as practiced on the Lewis and Clark Expedition and has been a popular speaker on the topic.

1. William Clark journal, codex G, p. 28, American Philosophical Society. Philadelphia, Pennsylvania (hereafter APS).

2. Gary E. Moulton, ed., The journals of the Lewis and Clark Expedition, April 17 1805 3uly 27 1805, 12 vols.(Lincoln, 1987), 4:435.

3. In addition to sources listed in notes 4 and 6, information about the medical aspects of the Lewis and Clark Expedition can be found in Eldon Chuinard, Only One Man Died: The Medical Aspects of the Lewis and Clark Expedition (Glendale, Calif., 1979), 301-4; Howard J. Beard, "The Medical Observations and Practice of Lewis and Clark," Scientific Monthly, 20 (May 1925), 506-26; Cindy Fent, "Some Medical Aspects of the Lewis and Clark Expedition," North Dakota History, 53 (Winter 1986), 24-28; Olaf Larsell, "Some Medical Aspects of the Lewis and Clark Expedition (1804-1806)," Surgery, Gynecology, and Obstetrics, 85 (November 1947); Doane Robinson,

"Some Medical Adventures of Lewis and Clark,'' South Dakota Historical Collection, 12 (1924), 52-66; and Donald D. Snoddy, ed., "Medical Aspects of the Lewis and Clark Expedition," Nebraska History, 51 (Summer 1970).

4. Clark's fever at Three Forks has been overlooked in most writing on the expedition's medical aspects, including Paul Outright, Lewis and Clark: Pioneering Naturalists (Urbana, Ill., 1969); and Paul Outright, "I Gave Him Barks and Saltpeter," American Heritage, 15 (December 1963), 58-61, 94-101. Heretofore the only speculation about an infectious etiology of Clark's illness appeared in Ronald V. Loge, "`Two dazes of barks and opium': Lewis and Clark as Physicians," 59 Pharos (Summer 1996), 26-31.

5. Elliot Coues, ed., The History of the Expedition under the Command of Lewis and Clark, 4 vols. (New York, 1893), 2:471; Olin D. Wheeler, The Trail of Lewis and Clark, 1804-1806, 2 vols. (New York, 1904), 1:366.

6. Stephen E. Ambrose, Undaunted Courage (New York, 1996), 261; Chuinard, Only One Man Died. 303 repeated in Moulton, ed., Journals, 4:433 n. 9J; Will W. Drake, "The Medical and Surgical Practice of the Lewis and Clark Expedition," journal of the History ofMedicine, 14 (July 1959), 273-97 [reprinted as ``Lewis and Clark, Westering Physicians," Montana the Magazine of Western History, 21 (Autumn 1971), 2-17]; L. L. Stanley. "Medicine and Surgery of the Lewis and Clark Expedition," Medical Journal and Record, 127 (1928) 364; James P. Rondo, Lewis and Clark among the Indians (Lincoln, 1984), 138.

7. "I believe . . . the inexperienced and presumptuous band of medical tyros let loose upon the world, destroys more of human life in one year, than all the Robinhoods, Cartouches, and Macheaths do in a century." Thomas Jefferson to Dr. Caspar Wistar, June 21, 1807, reprinted in Chuinard, Only One Man Died, 415-17.

8. Richard Dillon, Meriwether Lewis (New York, 1965), 11.

9. Donald Jackson, ed., Letters of the Lewis and Clark Expedition (Urbana, III., 1962), 18.

10. Ibid.

11. Ibid., 54-55. Two copies of these rules for Lewis were made.

Rush sent one copy to Jefferson after Lewis's visits: the other copy is in Benjamin Rush, Commonplace Book, p. 268, APS. These rules were standard maxims found in Rush's writings since 1777.

12. Based on Rush's list, William Clark prepared a similar but expanded list of "Inquiries relitive to the Indians of Louisiana," including nineteen questions related to physical history and medicine. Jackson, ed., Letters, 157-61.

13. Jackson, ed., Letters, 62-64.

14. Ibid., 80-81.

15. This valuable supply was nearly lost on May 14, 1805, when a sudden squall capsized the pirogue bearing many instruments, tools, and medicine. Had it not been far the alertness of Private Peter Cruzatte and Sacagawea, who recovered many items, the expedition would have sustained a serious loss. Moulton, ed., journals, 4:154.

16. Calomel, mercurous chloride, exerted a cathartic effect by direct irritation of the bowels. From the early sixteenth to the early twentieth century, it also was used extensively to treat syphilis. Jalap is a medicinal extract from the root of Exoganium purges, a Mexican morning glory, which also has a strong cathartic effect.

17. Well trained to observe, identify, collect, and preserve plant specimens, Lewis added extensively to new scientific knowledge and sent back sixty plant specimens from the Mandan villages for President Jefferson and the American Philosophical Society, including an unidentified plant highly prized by the Mandan and Hidatsa tribes "as an efficatious remidy in cases of bite of the rattle snake or Mad dog."Jackson, ed., Letters, 235. Outright believed this to be narrowleafed purple coneflower (Echinacea angustifolia). Outright, Pioneering Naturalists, 122.

There is little evidence that Lewis or Clark gleaned significant understanding of Indian medical practices. Although Lewis sometimes noted the Indians' medical application of an herb, these nostrums were not integrated into his own supply. Wild ginger, "a strong stomatic stimelent"; yellowroot, a "sovereign remidy for a disorder this quarter called the soar eyes"; horsemint tea; and the use of sweat lodges are notable Indian treatments mentioned in the journals. The captains did, however, supplement conventional medicines with poultices made from wild onions, slippery elm, or "coues" (biscuitroot). Pine resin, bear oil, and beeswax found use in ointments.

18. Moulton, ed., Journals, 4:423.

19. Ibid., 4:405.

20. Ibid., 4:417.

21. Ibid., 4:427. Lewis's party was two days behind Clark's, so this journal entry had to have been written on July 27, after Lewis rejoined Clark and had been updated about the previous days' events, including Clark's infirmity.

22. Ibid., 4:432.

23. Ibid.

24. Private Whitehouse and Sergeants Ordway and Gass all expressed concern that Clark was very ill in their journals. These comments, significant because these men rarely referred to illnesses, probably reflected the concern of all corps members.

25. Moulton, ed., Journals, 4:436. Medical theory of the early nineteenth century held that "Bathing the feet in warm water often prevents a fever in its forming state." Dagobert D, Rune, ed., The Selected Writings of Benjamin Rush (New York, 1947), 231.

26. In his instructions to Lewis, Rush's recommendation for constipation (costive) was a purge brought on by two of his pills every four hours until the bowels operated freely. He had initially written instructions to take three or four pills but tempered his zeal by crossing out the higher dose and writing in "2 pills." Apparently, not even Dr. Rush was always sure of the proper dose of his pills. (Photo of his handwritten list provided by author.) Rush, Commonplace Book, June 11, 1803, APS.

27. For Sacagawea, who had been seriously ill earlier that summer, Clark had administered the standard treatment of repeated bleedings. Just four weeks earlier, Private Whitehouse became ill after drinking too much water when fatigued and overheated. Lewis did not hesitate to apply venesection to the private. Not having his lancet at hand at that moment, Lewis bled Whitehouse using a pen knife and was quite satisfied with the results.

28. Gary E. Moulton, ed., The Journals of the Lewis and Clark Expedition, The journals of Patrick Gass, 12 vols.(Lincoln, 1996), 10:119. See also Gary E. Moulton, ed., The Journals of the Lewis and Clark Expedition, July 28, 1805-Novemeber 1, 1805. 12 vols. (Lincoln, 1988), 5:7-9.

29. Biddle indicated residual fever on July 29: "Captain Clarke's fever has almost left him, but he still remains very languid and has general soreness in his limbs." Paul Allen, ed., History of the Expedition under the Command of Captains Lewis and Clark, 2 vols (Philadelphia, 1814), 1:326-31. When Biddle prepared his narrative of the Lewis and Clark journey, he consulted Clark to clarify descriptions and ferret out details. This consultation in the process of preparing the journals took place about 1810, four years after conclusion of the

expedition, In this first published comprehensive document, Clark's illness is not presented in the same light as in the journals. Biddle diminished the severity of the illness significantly.

30. Lewis said he Was pleased with the results of the purgative he employed the previous day for his diarrheal illness,

31. Neither Lewis nor Clark had mentioned this painful swelling during Clark's confinement at the Three Forks.

32. Private Joseph Whitehouse noted an encounter with a rattlesnake on July 11, 1805, near present-day Ulm, Montana, when he wrote that he "trod on a verry large rattle Snake. it bit my leggin on my legg I Shot it." Gary E. Moulton, ed., The Journals of the Lewis and Clark Expedition, The journals of Joseph Whitehouse May 14, 1804-April 2, 1806, 12 vols. (Lincoln, 1997), 11:223.

33. Moulton, ed.,_Journals, 5:47.

34. Ibid., 5:62-63; Rune, ed., Selected Writings, 234.

35. Rune, ed., Selected Writings, 234.

36. In 1880, the causative parasitic organisms, plasmodia, were first seen in a film of fresh blood under microscopic examination. In the 1890x, Ronald Ross, a British army surgeon in the Indian Medical Service, recognized developing plasmodia in mosquito guts. He received the Nobel Prize in 1902 for establishing the life cycle of plasmodia.

37. Gary E. Moulton, ed., The Journals of the Lewis and Clark Expedition, August 30, 1803-August 24, 1804, 12 vols. (Lincoln, 1986), 2:86.

38. Ibid.

39. Rune, ed., Selected Writings, 234.

40. Lewis and Clark documented using Rush's pills elsewhere in the journals. On March 7, 1805, a Mandan chief named Coal brought Clark a sick child to whom the captain administered the pills. On February 16, 1806, while at Fort Clatsop, the captains gave Rush's pills to Private Gibson as treatment for an "obstenate" fever. The notation was accompanied by an enthusiastic endorsement of Rush's medicine.

41. First quotation from Gary E. Moulton and James J. Holmberg, "`What We Are About': Recently Discovered Letters of William Clark Shed New Light on the Lewis and Clark Expedition," Filson Club History Quarterly, 65 (July 1991 ), 387-403; second quotation from James J. Holmberg, "The Lost Letters of William Clark," paper presented at the Lewis and Clark Trail Heritage Foundation Annual Meeting, Bismarck, North Dakota, August 4, 1999.

42. Lewis noted this second illness in his journal when he wrote on November 22, "at the expiration of this course saw some Heth hens or grows-one ofmy men went on shore and killed one, ofwhich we made some soup for my friend Capt. Clark who has been much indisposed since the l6th[.j" Moulton, ed.,Journals, 2:101. Chicken soup to treat illness enjoys a long history.

43. Quotation from James J. Holmberg, communication with the author, October 11, 1999. In a letter written on August 15, 1811, to Nicholas Biddle, Clark described his military experience, noting that after serving in the army in the 1790s, "I resigned and returned to a Farm in Kentucky on which I lived several years in bad health." Jackson, ed., Letters, 572. Lewis's invitation to be cocaptain and "to participate with me in it's fatiegues, it's dangers and it's honors" was answered by an eager and enthusiastic Clark, who must have felt that he was in excellent enough health to endure the expected hardships. Jackson, ed., Letters, 60.

44. On tick-borne diseases, see Lynette Doan-Wiggen, "Tickborne Diseases," Emergency Medicine Clinics of North America, 9 (May 1991), 303-25.

45. Rickettsia area class of small bacteria, transmitted to humans by ticks and fleas, that cause a variety of human diseases. On the impact of RMSF in Montana history, see Philip A. Kalisch, "Rocky Mountain Spotted Fever; The Sickness and the Triumph," Montana The Magazine of Western History, 23 (Spring 1973), 44-55.

46. At the Great Falls of the Missouri, Lewis described a mammal new to science, the thirteen-striped ground squirrel, a common tick host. See Moulton, ed., Journals, 4:367.

47. For a detailed description of the clinical aspects of CTF, see Hewitt G. Goodpasture et al., "Colorado Tick Fever: Clinical, Epidemiologic, and Laboratory Aspects of 228 Cases in Colorado in 1973-1974," Annals of Internal Medicine, 88 ( 1978), 303-10.

48. CTF data from Montana in 1981-1995 is courtesy of Todd Damrow, state epidemiologist, Montana Department of Public Health and Human Services, letter to author, November 13, 1996.

49. Quoted with permission from William S. McBride, June 18, 1850, in `Journal of an Overland Trip from Gooshen, Indiana to Salt

Lake City, March 31st June 26th, 1850," MS HM16959, Huntington Library, San Marino, California.

50. Noxon Toomey, "Mountain Fever and Spotted Fever of the Rocky Mountain-Clinical Studies," Annals of Internal Medicine, 5 (1931), 585-600; Noxon Toomey, "American Mountain Tick-Fever and Spotted Fever of the Rocky Mountains-Comparative Epidemiology," ibid., 601-12.

Claude Moore Health Sciences

Library. University of Virginia, and

Robert Fishman. M.D.

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