Catherine Wilbourne
Bio 1615
Article Paper
November 9, 2014
Outbreak of Tick-Borne Relapsing Fever at the Grand Canyon
The most common occurrences of tick-borne relapsing fever occur in people
who have had recent stays in cabins in which rodents have recently nested. It is a
form of Borrelia hermsii. These outbreaks were highly reported in areas and cabin in
which rodents were prevalent. The illness itself is an acute illness in which infected
peoples experience such symptoms as fever, sweats and headaches. Usually those
infected experience a period of remission where their symptoms are not present
however with this particular strain their ends up being a relapse.
An initial outbreak of the virus was reported in the year 1973 at an area
along the north rim of the Grand Canyon; there were sixty-two reported cases. The
reason scientists have started looking back into the outbreak is because recently
there have been a handful of new cases reported. The goal of scientists was to look
at the initial outbreak and examine the cabins that had been rodent-proofed after
the first outbreak and compare them to the recent spread of infection and the cabins
that were not rodent proofed after the 1973 outbreak. This allowed scientists to
take a look at the effectiveness of the preventative measures taken and the recent
spread of disease.
After the outbreak in 1973 scientist began to conduct research into the
spread of the disease, they first gave park visitors and employees questionnaires
regarding their symptoms and the onset of symptoms as well as the timeline of their
visits. This allowed them to rule out people experiencing symptoms of anything
other than TBRF and pinpoint the time and place. When they could, scientists also
gathered serum samples from patrons showing symptoms, for antibody tests. This
led to the conclusion that there had been a legitimate outbreak and they were able
to trace the disease back to rodents living in the cabins at the camp.
There were two groups of cabins, a northwest group and a southwest group
and they were separated by a road. After 1973 the southwest group was rodent
proofed. This included removing thousands of lbs. of nesting and other materials as
well as structural updates to the buildings to prevent rodent access. This allowed for
a comparison to be made between the two groups after two cases of TBRF were
reported in 1990 from visitors who had stayed at the lodge. These two cases were
traced back to the northwest group of cabins, the group that had not been initially
rodent-proofed. So scientists began to assess the effectiveness of the precautionary
measures taken.
The expectation was that the cabins that were not rodent-proofed were the
cause of further infection and that rodent proofing the southwest group prevented
further infection in employees and visitors that stayed in those cabins. To start off,
questionnaires were sent out to nearly 7,000 visitors and 200 employees regarding
their stay and their symptoms. Of those, only about half of the visitors and seventyfive percent of employees responded. 93 visitors and two employees reported
symptoms, further interviews were conducted and it was found that 2 confirmed
cases and 13 probable cases were recorded (Paul, Maupin, Scott-Wright, Craven &
Dennis, 2002). ELISA form of serological testing, used for diagnostic testing, uses
antibodies and color changes to identify certain substances (Serology, 2014) was
used on serum samples from employees and visitors to determine actual cases.
Scientists were able to use this information to gather a baseline for infected vs. noninfected persons and in which group of cabins there were recent outbreaks.
Environmental surveys on the cabins showed that specific cabins associated
with TBRF allowed for ample access to rodents, especially in the northwest group
that had not been treated after the outbreak in 1973. Overall, there was insufficient
evidence and problems with gathering information for the study due to language
barriers, low numbers of responses, time-lapse prior to obtaining specimens as well
as the recollection of events by patrons, making it nearly impossible to link the
outbreaks directly to the rodents. However, the number of cases did significantly
drop once rodent proofing methods were implemented. This would imply that there
is some sort of connection, but there is not significant evidence to incriminate the
rodents.
References
Paul, W. S., Maupin, G., Scott-Wright, O., Craven, R. B., & Dennis, D. T. (2002).
Outbreak of tick-borne relapsing fever at the north rim of the grand canyon:
Evidence for effectiveness of preventative measures. 71-75.
Serology. (2014, October 24). http://en.wikipedia.org/wiki/Serology Retrieved
November 11, 2014.