Study Results: Tick-borne Disease Risk to Appalachian Trail Hikers, Karl Ford, Ph.D.

[earthford]

One of the major hazards of hiking the AT is exposure to tick-borne disease. While thru-hiking the AT in 2013, I conducted tick research for the National Park Service to determine the extent of tick exposure in shelters and camping areas relative to trail hiking.

Various diseases are transmitted by ticks present on the AT, including Lyme disease. About 33,000 cases of Lyme disease were reported in the US in 2011, with high incidence in the New England and mid-Atlantic eastern states of PA, MD, NJ, NY, CT, MA, VT, NH, and ME through which the AT traverses. The disease is transmitted via the deer tick Ixodes scapularis which occurs in deciduous forests of the Appalachians and other areas. Each year over 3-4 million people hike the Appalachian Trail where they risk contact with infected ticks. Lyme disease not only causes a flu-like illness, but can cause poorly understood longer-term debilitating chronic Lyme disease syndrome in up to 20-50% of the cases. Lyme disease is a significant health risk to uninformed and ill-prepared hikers (and many are uninformed and ill-prepared). Babesiosis and human anaplasmosis are two other pathogens associated with deer ticks.

Other tick-borne pathogens are also known to occur along the AT. The lone star tick Ambylomma americanum and the American dog tick Dermacentor variabilis are also vectors of ehrlichiosis and spotted fever rickettsia diseases. A. americanum can also cause a red meat allergy. These ticks are more prevalent is the southern states and tend to be found more in herbaceous areas.

There are approximately 286 primitive three-sided camping shelters on the AT. The shelters are often infested with mice and other rodents, reservoirs for the Lyme disease bacterium B. burgdorferi. Because so many hikers congregate and sleep in the shelters and because of the mice infestations, I wanted to know whether shelters and tenting areas present any greater risk of contacting ticksthan hiking the Trail.

With NPS approval, I sampled forty-two shelter areas along the entire AT in a south to north transect using a stratified random sample. At each selected shelter, the procedure was to tick-flag three study groups: (1) the approximately 10 m² of shelter floors, (2) a 100 m² polygon surrounding the shelter; (3) as a control, 500 x 0.5 m linear swath of trail. The second group assessed risk to those camping in tents and tarps. I used a 0.5m² white cloth hand flag to sweep surfaces and vegetation to collect ticks. I shipped the ticks to the U.S. Army Public Health Laboratory in Aberdeen MD for species identification and pathogen detection.



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Flagging for ticks Bug-net Pants Tick Nymph Attached


I collected thirty-three adult and nymphal ticks, of which 20 were A. americanum, 10 were D. variabilis, and 3 were I. scapularis. Pathogens detected by the laboratory include: rickettsiae and erlicichiae in one D. variabilis, and Borrelia burgdorferi in an adult Ixodes scapularis. Despite efforts, no ticks were collected from GA, NC, TN, MD, NY, CT, VT, NH and ME. While sampling occurred from mid-April until late August,, ticks were only collected between May 29 and July 21; other dates failed to collect ticks. Eighty-eight percent of ticks (29) were collected from the Trail, while only 6% (2) were collected from shelters and 6% (2) were collected from tenting areas.

Ticks were generally not found in shelters despite sampling 42 shelters. Of the two shelter ticks, one was actually found dead inside a shelter and may have been carried in from hikers; the second was found on shelter steps. Ticks were also generally not found in tenting areas. Many shelter areas have little understory vegetation or leaf litter to support questing ticks due to trampling or trimming/mowing by volunteers. Relative exposure can be estimated from the tick collections. From the data in this study, Trail tick exposure was 14.5 times both shelters and tenting areas, despite the fact that the overnight hikers spend over half of their day in the shelter areas.

All of the ticks collected were in the higher risk states for deer ticks, e.g. northern VA, PA, NJ, MA. While no ticks were collected in MD, NY, and CT, these states are high risk also. Average elevations in these states tend to be much lower than the Trail average of 2,500’ hence are more suitable tick habitat.

The number of ticks collected in this study is relatively small. The lack of collections in the spring is probably due to the early season and high elevations of the AT in GA, NC and TN. Much of the vegetation had not leafed out in GA, NC and TN and night-time temperatures were near freezing in April and early May. Several residents told me that the tick populations were low in 2013 compared to other years.

Similar to the southern states, the elevation of the AT, combined with the more northern latitudes and sub-alpine coniferous forest and alpine areas may explain why no tick collections were made in the northern states of CT, MA, VT, NH and ME. No ticks were collected above 2,720’ nor in sub-alpine or alpine areas. About half of the overall Trail exceeds that elevation, often in sub-alpine or alpine environments which occur frequently in VT, NH, and ME. The coniferous sub-alpine and alpine environments of the AT vary in elevation with latitude and are poor tick habitat.

Tick exposure can be managed by regular trail, field, powerline, and shelter area trimming and by sweeping shelters out prior to sleeping. Most importantly, hikers can proactively reduce their risk by wearing permethrin-treated clothing and equipment, use of 20-30% DEET in exposed skin, staying on the Trail and avoiding hiking off-trail, such as in collecting firewood. A daily tick check is very important but hard to accomplish on the Trail. Juvenile (nymph) stages are so small they are often not noticed except by careful skin checks. I wore treated bug-net pants and treated shirt and hat and had zero ticks on my body.

Most hikers I met on the Trail had ticks attached and several had been treated for Lyme disease because they did not follow these precautions. More tick awareness posters in general for the higher risk states of northern VA through CT are recommended. Hikers should be able to identify deer ticks, know symptoms of Lyme disease and seek treatment immediately if any symptoms of Lyme disease appear. It is possible to safely hike the trail if these precautions are followed.

A scientific paper is in preparation for a scientific journal. Questions can be sent to me at [email protected].

[1234]

Thanks for doing the study. Nice to know. I have found ticks to be found mostly where animal populations are higher, mostly deer and squirrels. (wild) Animal populations are not high around shelters. I live in a rural area with a high population of ticks and pull one or 2 off every day in spring when I walk to feed the chickens. I have not had lyme but my wife had it once.

[stranger]

It's also funny how many people think ticks carry Lyme...MICE carry lyme, then ticks bite mice, then us...

[ladydi]

I think you may be arguing semantics...? Of course the ticks carry the spirochete which causes Lyme. There are now more tick borne illnesses than first thought. Somewhere I had an interesting article about how the spirochete can change to a cyst and hide in interstitial tissue then emerge later to cause more damage. The article went on to suggest that many other diseases diagnosed may actually be a form of Lyme. You may be able to check it out should you be so inclined.

[ChuckT]

The results are somewhat surprising! More ticks on the foot-path then in or around the shelters.

Here in Fla. I believe that most ticks are picked up from the grass and other plants that overhang the footpath and have been warned that pine straw is another rich enviornment for tick population.

The sum of the above may be to use the established shelters instead of spreading out and away from pre-used sites?

Cvt

[Paul the Brit]

If you haven't watched Under Our Skin it's worth a watch: http://topdocumentaryfilms.com/under-our-skin/