Where are the ticks? Solving the mystery of a tickborne relapsing fever outbreak at a youth camp.
The Flagstaff Unified School District (FUSD) has operated Camp Colton as a youth camp since 1971. Each year FUSD provides weeklong residential outdoor learning experiences at the camp to about 1,000 local sixth graders on a rotational basis, beginning shortly after the start of school. The camp is located about eight miles north of Flagstaff, Arizona, at 7,000 feet above sea level, and is surrounded by one of the largest Ponderosa Pine forests in the world (Friends of Camp Colton, 2014).
On a Sunday evening in August 2014, the Coconino County Public Health Services District in Flagstaff, Arizona, was notified by a local hospital that four high school students had been admitted exhibiting symptoms of high fever, chills, and body aches. One of the students was considered to be in serious condition.
Prior to the onset of their symptoms, the students had been staying in an old log cabin at Camp Colton, which is located at the base of the San Francisco Peaks (see photo on page 9). The students were performing public service by cleaning and refurbishing the cabin in preparation for the seasonal opening of the youth camp.
The symptoms displayed by the students mimicked a number of enzootic diseases encountered in the northern region, including hantavirus and plague. Initially, the suspect disease was thought to be hantavirus, since two such cases had recently occurred in and around Flagstaff, one of which was fatal. Moreover, prior to becoming ill the students participated in cleaning activities that exposed them to rodent feces and dust. The initial blood results ruled out hantavirus and identified spirochetes, tickborne relapsing fever (TBRF), which is treatable with antibiotics, as the cause of illness. The camp was closed immediately and an environmental investigation was scheduled for the following day.
Tickborne Relapsing Fever (TBRF)
TBRF is endemic in many parts of Coconino County. The disease-causing agent is a bacterial genus called Borrelia. The most common species that may cause human disease is B. hermsii (Heymann, 2008). TBRF is transmitted from the bite of an infected soft body tick (family Argasidae) of the genus Ornithodoros. Soft ticks, unlike hard ticks, do not stay attached to their host. A soft tick feeds on the host at night and returns to the host nest after feeding. Soft ticks will feed on humans when their rodent host dies (Centers for Disease Control and Prevention [CDC], 2012). The incubation period for TBRF in humans is usually 2-18 days with an average of seven days (Heymann, 2008). TBRF is characterized by relapsing episodes of fever accompanied by a variety of other symptoms, with each fever episode ending with a "crisis" that includes a chill phase and a flush phase (CDC, 2012).
History of TBRF Outbreaks in Coconino County
Prior to this outbreak, the last outbreak of TBRF in Coconino County occurred in August 2009 in a cabin located about 19 miles north of Flagstaff in the national forest. One confirmed case and three probable cases occurred. All cases stayed in the cabin. In response to the outbreak, the cabin, which the Forest Service rents to the public, was closed and treated for ticks and fleas, with all cracks and crevices permanently sealed. Although it is known that soft ticks are the only vector for TBRF, no soft ticks were found or trapped.
Earlier outbreaks were recorded at the North Rim of the Grand Canyon: one in 1990 with 17 confirmed cases and the other in 1973 involving 62 cases. No data exist, however, about whether ticks were recovered. Typically, soft ticks are found in rodent nesting material (Wheeler, 1942). The failure to find ticks in this outbreak as well as in the cases cited previously has hindered efforts at developing appropriate mitigation strategies. In order to prevent TBRF, the habits of soft ticks must be established. The central issue confronting environmental health professionals is, "Where are the ticks?"
The health district interviewed 26 of the 45 students and staff who stayed at the Camp Colton cabin August 1 through August 3, 2014. Spirochetes were confirmed in initial blood samples screened by the acting hospital and B. hermsii was confirmed in blood samples by the Centers for Disease Control and Prevention. Approximately 41 students and staff slept inside the cabin. Of the 41 who slept inside the cabin, six were confirmed and five were probable cases of TBRF (Figure 1). All confirmed and probable cases fully recovered from TBRF.
Concurrent with the epidemiological investigation, the health district coordinated an investigation of the camp and surrounding area. Dr. Nathan Nieto with Northern Arizona University, who is a TBRF expert, was invited on the investigation to collect samples for analysis.
During the environmental investigation, all aspects of the camp were inspected. Evidence of rodents and nesting materials was found in the two open lofts of the main cabin where the students slept as well as throughout the first floor around the kitchen where the staff slept and in the basement area (see photos on page 10, top). During the investigation the camp director indicated that a pest control company was hired to remove rodents from the cabin about a month before students arrived, but the cabin had not been treated for ectoparasites such as fleas and ticks.
Live rodent traps (Sherman traps) were set inside and outside the main cabin by Dr. Nieto (see photo on page 10, bottom). Two chipmunks, two mice, and two voles were caught. One chipmunk (Eutmanias dorsalis) and one deer mouse (Peromyscus maniculatus) tested positive for TBRF Dr. Nieto also collected rodent nesting material that was sieved for ticks, but no ticks were found. As in previous investigations, this was a concern because without finding the ticks the vector of this disease could not be verified. Once again the investigators were left wondering, "Where are the ticks?"
After the investigation was completed the health district environmental assessment was written and provided to the camp director. The environmental assessment included a list of items that needed to be corrected prior to reopening. Items on the list included treatment for ectoparasites by a state licensed pest control company and sealing penetrations, holes, cracks, and crevices throughout the inside of the old log cabin. The basement located under the old cabin was cluttered, which provided harborage for rodents and was therefore added to the remediation list of areas to be cleaned out. The dry food store room for the kitchen also needed to be cleaned and organized, with all boxed and plastic wrapped food items to be stored in rodent-resistant containers.
Solving the Mystery
To this point investigators had searched for ticks based on the conventional assumption that they would be found in rodent's nesting material. As in previous outbreaks no ticks were found. Then the search was extended to areas of the cabin where ticks would not typically be found. Expanding the search protocols yielded unexpected results. Black tarry spots were found along the window frames in both the upstairs and downstairs windows (see photo on page 11, left). Closer examination revealed these spots to be digested blood deposited by ticks. Further examination revealed a few remaining ticks that were hiding in cracks along the windows, and both live and dead specimens were found behind pictures near the windows, which are located in close proximity to the sleeping areas (see photo on page 11, right).
Finding soft body ticks harboring in window frames and in cracks and crevices of walls is unusual. Typically soft body ticks are found in rodent nesting material where they have easy access to their hosts for blood meals. In this case, however, it appears that the ticks changed their habits in order to gain access to both rodent and human hosts, enabling the ticks to make seasonal transitions. During off-season months, hosts consisted of rodents and during the months the camp operated, the primary hosts were humans. To accommodate this dramatic change of hosts over the course of a year, it appears the ticks adopted behaviors typically encountered in bed bugs.
The camp was reopened after the cabin was retreated in the areas where the ticks were found and after both the cabin and basement had been completely cleaned, removing all unnecessary articles and sealing cracks and crevices. As an added precaution, staff and students slept in newly constructed structures located away from the log cabin.
Following the tick hiding place discoveries made at Camp Colton, health district investigators revisited the Forest Service cabin, which was the site at the 2009 TBRF outbreak. Back at the Forest Service cabin, black tarry spots were found on the surfaces of the windowsills adjacent to the sleeping areas. The Forest Service closed the cabin and treated the identified areas for soft ticks. This investigation provided new information into the feeding habits of ticks, helping solve the mystery. Now that it is known where the ticks are, this information will be applied for future TBRF outbreaks.
Marlene Gaither, REHS, MPH, ME
Coconino County Public Health
Nathan Nieto, PhD
Biological Sciences Department
Northern Arizona University
Coconino County Public Health
Acknowledgements: Marie Peoples, PhD, chief health officer, Coconino County Public Health Services District; Randy Phillips, division manager, Coconino County Public Health Services District; Trish Lees, public information officer, Coconino County Public Health Services District; Eric Bohn, environmental specialist 1, Coconino County Public Health Services District; David Engelthaler, PhD, general manager, TGen Translational Genomics Research Institute; LCDR Jefferson Jones, MPH, MD, U.S. Public Health Service, Epidemic Intelligence Service officer, Centers for Disease Control and Prevention, Arizona Department of Health Services, Maricopa County Department of Public Health.
Corresponding Author: Marlene Gaither, Environmental Health Program Manager, Coconino County Public Health Services District, 2625 North King Street, Flagstaff, AZ 86004. E-mail: email@example.com.
Centers for Disease Control and Prevention. (2012). Tickborne relapsing fever. Retrieved from http://www.cdc.gov/relapsing-fever/
Friends of Camp Colton. (2014). Camp Colton. Retrieved from http://friendsofcampcolton.org/camp/
Heymann, D. (2008). Control of communicable diseases manual (19th ed., p. 511). Washington, DC: American Public Health Association.
Wheeler, C. (1942). A contribution to the biology of Ornithodoros hermsi Wheeler, Herms, and Meyer. The Journal of Parasitology, 29(1), 33-41.
FIGURE 1 Epidemiologic Curve: Tickborne Relapsing Fever Outbreak, August 2014 Date Confirmed Probable 8/3 1 8/4 1 8/5 8/6 2 1 8/7 1 8/8 1 8/9 1 1 8/10 1 8/11 1 Note: Table made from bar graph.
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|Title Annotation:||ADVANCEMENT OF THE SCIENCE: SPECIAL REPORT|
|Author:||Gaither, Marlene; Schumacher, Mare; Nieto, Nathan; Murray, Jennifer Corrigan Hugh; Maurer, Matt|
|Publication:||Journal of Environmental Health|
|Article Type:||Cover story|
|Date:||Apr 1, 2016|
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