DANGER IN THE BITTERROOT
VALLEY:
EARLY STRUGGLES WITH SPOTTED
FEVER
One of America’s most
idyllic spots, the Bitterroot Valley, nestled between two mountain ranges in
southwest Montana, seemed a healthy place. Lewis and Clark, passing through the
Valley, and native-American peoples living there did not
manifest unusual illness.
After the Civil War settlers moved in, felling thousands of trees in the western
side of the Valley to feed a burgeoning lumber industry. Scrub vegetation,
populated with small mammals, replaced the trees. By the 1880s scattered cases
of a “spotted fever” were reported, usually fatal, most coming from the west
side of the Valley, and most showing recent tick bites. Between 1895 and 1902 64
people died out of 88 with the disease.
 |
| Bitterroot Valley today (Wikipedia) |
In 1902 two
investigators from the University of Minnesota, Louis Wilson and William
Chowning, suggested the wood tick as a vector and found organisms in the blood
of victims they believed were a type of Pyroplasma, similar to that causing
Texas cattle fever, another tick-transmitted disease. The notion of insects
transmitting disease was popular. In the previous 25 years mosquito
transmission of filaria, malaria, and yellow fever, and tick transmission of
Texas cattle fever had all been discovered.
Getting rid of ticks,
though, by burning brush and killing animal hosts didn’t reduce the disease
incidence. Other
investigators cast doubt on the tick theory, adding confusion,
until the arrival of Howard Ricketts and William King. They were able in 1906 to
infect guinea pigs and to prove that ticks transmitted the disease. Ricketts
also thought he saw tiny microorganisms he believed were the disease agents but
could not culture them. Stymied by an interruption of funding, Ricketts left
for Mexico to study typhus (another spotted fever). He perished in Mexico,
tragically, from that very disease.
 |
| Howard Ricketts, martyr to typhus (Wikipedia) |
Ricketts had recommended
learning more about wood tick habits, enticing Robert Cooley, Montana State
entomologist, to step in. Cooley employed Willard King and Clarence Birdseye
(who later founded the frozen food industry), both field biologists, to collect
ticks and wild animals for study. The work was hazardous. Their lab was set up
in an old two-room log cabin in which one man had died of
spotted fever. The
yard, full of ticks, was burned, then sprayed with kerosene (a tick repellant),
and the team slept in tents around the cabin. As they worked collecting animals
and ticks they wore high shoes, with tight kerosene-soaked khaki leggings above
them, and doused their outer clothing with kerosene. They stripped and
inspected each other for ticks every two hours. Somehow they remained healthy.
 |
| Cabin and tent of Cooley's team, Bitterroot Valley (National Library of Medicine) |
The team demonstrated
a 2-year cycle from egg to adult tick and showed that adults fed primarily on
large domesticated animals. As a result dipping centers were set up to
“de-tick” farm and domestic animals. But, related to poor dipping agents and
bureaucratic infighting, the program foundered and spotted fever (now called
Rocky Mountain spotted fever) claimed more victims.
What about the
supposed causative agent, Pyroplasma? No one else could find it. S. Burt
Wolbach, a young Harvard pathologist, saw tiny intracellular organisms,
particularly in vascular endothelial cells, that he could not grow and which he
named Dermatocentroxenus rickettsii,
in honor of Ricketts (later renamed Rickettsia
rickettsii). They were a new type of organism that grew only in cells, the
details of which had to await further developments in technology.
In the era before
antibiotics the main strategy against infectious diseases was vaccination, and
so it was with the spotted fever.
Roscoe Spencer, a US Public Health Service
physician, and Ralph Parker, a Montana entomologist, working in an abandoned
two-story brick schoolhouse in Hamilton (in the Valley) in the 1920s,
discovered that injecting material into guinea pigs from ground-up infected
ticks, sterilized with formalin and phenol, could produce an imperfect but
substantial immunity. Spencer developed this into a commercial vaccine.
 |
| Roscoe Spencer (National Library of Medicine) |
Vaccine production
was a cumbersome process. Each year’s supply required collection of 30-40,000
adult ticks to feed on 4 to 6,000 rabbits and 20-30,000 guinea pigs. The adult
ticks were fed on rabbits, then collected for egg laying. The hatched larvae
were fed on newly infected rabbits, dropped off, and molted into nymphs. The nymphs
fed on more rabbits (400/rabbit), were
collected, dried with hair dryers, and
kept at 22 degrees C to molt into adults. The adults were stored at near freezing
levels for 6-12 months (to enhance vaccine efficiency), after which they were
warmed up and fed on guinea pigs. Swollen with blood, they were emulsified in a
Waring blender with formalin, phenol, and saline. Finally, after storage, further
dilution, and purification, the vaccine was ready, and was accepted by
residents.
 |
| Brick schoolhouse where original vaccine work was done (National Library of Medicine) |
The toll was heavy. In the process three
laboratory workers died of spotted fever. Others, including Spencer, Parker,
and a third all developed tularemia, a tick-born disease originally discovered
in Tulare County, California (they survived). Spencer, depressed, was
transferred back east. The head of the tick-rearing room resigned, and Parker
carried on as chief in a new, safer laboratory building.
The tick-based vaccine
continued to be produced by the Rocky Mountain laboratory until 1948 when it
was replaced by an egg yolk-derived vaccine and the advent of antibiotics. There
is no vaccine available today. The laboratory continues as a
Once considered a
localized disease, Rocky Mountain spotted fever has been found throughout much
of the U.S., primarily in the central eastern and mid-western states. Its
history could be said to have had a “rocky” beginning, with false starts and at
least three martyrs.
SOURCES:
Harden,
Victoria. Rocky Mountain Spotted Fever:
History of a Twentieth Century Disease. 1990; J Hopkins Univ. Press.
Price,
Ester. Fighting Spotted Fever in the
Rockies. 1948; Naegele Printing Co. Helena.
Ricketts,
H. “The Transmission of Rocky Mountain Spotted Fever by the bite of the Wood
Tick (Dermacentor occidentalis).
1906; JAMA 47: 358.
Spencer,
R and Parker, R. “Rocky Mountain Spotted Fever: Vaccination of Monkeys and Man.
1925; Public Health Reps 41: 2159-67.
Wolbach,
S B. “Studies on Rocky Mountain Spotted Fever”. 1919; J Med Research 41:3.
