May 17 2017

The Threat of Tick-Borne Disease to Cyclists, Campers, Hikers, and Paddlers by Tamia Nelson

Global warming and mass tourism are breaking down barriers to the spread of formerly rare diseases born by ticks. If you’re a bacterium, a protozoan pathogen, or a virus, this is good news. But if you’re a cyclist, camper, hiker, or paddler, it’s not so great. Is the spread of tick-borne disease a tick(ing) time bomb?


To make a long story short, in early spring last year I picked up a hitchhiker when on a short hike through deer country. Here she is in situ:

Sister Traveler in Situ

It’s not a great photo, so I’ve outlined her body in the accompanying black-and-white shot to make her easier to see. She’s wasn’t much bigger than the head of a straight pin. The bruise left by her excavations was three times as large as she was. And yes, she was a “she,” a female deer tick (Ixodes scapularis). The proportions of the scutum (the dark dorsal “shield” visible in the photos below) give the game away.

A Parting of the Ways

As you can see, we parted company before she could drink her fill. Her comparatively svelte figure tells you that. Now here’s a closer look at a second tick — Farwell plucked this one from his thigh a couple of years back — displaying the belly of the beast:

A Ventral View

The saw-like hypostome, visible in the upper right of the photo, is the tick’s sheet anchor, and because Farwell’s clumsy surgery left the shielding palps behind — he dug them out of his flesh later — you can get a particularly good view of his wee tormenter’s barbed holdfast. That toothy hypostome also explains why removing a tick can be a rather, er, ticklish job. The sawteeth serve the same purpose as the barbs on a harpoon. But so deft is the little beast that her initial thrust is painless. At least it was in my case.

I scrubbed the skin around the wound with isopropanol, and the next day I headed off to urgent care for a prophylactic dose of doxycycline. I had more luck than I deserved. A Lyme titer run on blood drawn five weeks later was negative. It seems that Nemesis was content to let me off with a warning. This time.

ARE YOU FEELING LUCKY?

Or would you rather take steps to avoid trouble in the first place? I bet I know the answer. And you’d be right to prefer prevention to cure.

Previously unaffected regions of the States and adjacent Canadian provinces are no longer a safe haven from Lyme disease and other tick-borne infections. The northern latitudes are warming up fast, and the ebb and flow of global tourism ensures that no infectious disease can remain confined to one location for very long.

Moreover, Lyme disease is far from the most serious tick-borne malady. Rocky Mountain spotted fever has already spread well beyond the bounds suggested by the name, and the Powassan virus — first reported in Powassan, Ontario, this virus can cause a deadly tick-borne encephalitis — is already established in tick populations throughout eastern Canada and the northeastern and midwestern United States. The upshot? We’ll be hearing a lot more about ticks in the years to come. So …

THE CLOCK IS TICKING

Suddenly ticks were big news. As the world slowly warms up, tick-borne diseases are being seen in places they haven’t been noticed before. Lyme disease-infected deer ticks were virtually unknown in New York’s Adirondack Mountains in 2005. Now they’re commonplace. Their steady northward advance continues, too. In short, we can’t run, and we can’t hide. (Unless we want to live life in a La-Z-Boy, and even then, we’d need to keep a close eye on Fido. Is he Breaking Bad?)

Still, you’re safe while ON and IN the water. Ticks aren’t aquatic. And neither are we. So whenever you need to meet nature’s call by parking your bike, leaving your boat, or stepping off trail to “water the bushes,” chances are good that ticks are waiting to welcome you. Camping in the wild? It’s dinner time for ticks!

TICKS ARE HARDY AND HARD TO SPOT

The six-legged larvae are smaller than a poppy seed. The eight-legged nymphs aren’t much bigger. Adults aren’t exactly megafauna.

Life Stages of a Deer Tick

The nymphs and adults cling to vegetation with their rear legs, extending their clawed forelegs in what some lyrical boffin has labeled questing behavior. When a suitable host passes by — be he a mouse, a moose, or a man — the leggy tick grabs hold and hangs on. Which is why every prudent person takes precautions. In other words, Be Prepared! You’ll find some suggestions at the CDC website.

In a hurry? Then here’s the executive summary:

  1. Wear long pants and a long-sleeved shirt when afield. Light colors are best — they make it easier to spot a prospecting tick.
  2. Pull your socks up (over your pants legs), and wear a hat with a wide brim. If you want extra protection, you can get clothing impregnated with permethrin, a highly persistent synthetic pyrethroid that kills ticks and mosquitoes on contact. But it also kills fish and aquatic invertebrates, and it sickens cats.
  3. If you have less enthusiasm for total environmental warfare may wish to eschew permethrin in favor of repellents like DEET or picaridin, a newish alternative.
  4. At day’s end, inspect your body. Give special attention to hairline, ears, armpits, groin, and the cleft between your cheeks. If you’re not a contortionist, you’ll probably need to ask a family member or friend to help. Don’t be shy. Then head for the showers. And be sure to wash your hair.

WHAT IF YOU FIND A TICK?

Remove it. Fine-point forceps will do the job, or you can use a “tick spoon.” (I followed the advice described by the University of Maine Cooperative Extension.) Dispatch the tick in the campfire or retain it to show the doc. Owners of alcohol cookers like the Trangia have an advantage here: They have a ready supply of preservative.

Once you’ve dislodged your unwanted guest, it’s just a matter of waiting to learn if you’ve been infected with a tick-borne pathogen. This isn’t as straightforward as it sounds. While the bull’s-eye rash often seen in Lyme disease is now a staple of summer recreation stories in local papers, it’s absent in a large proportion of cases, and the early symptoms of the “malaria-like” babesiosis (an increasingly common co-infection) are subtle and easily missed. That said, if you can see a doc within 72 hours, you can get a prophylactic dose of doxycycline to forestall Lyme disease. But be warned: This will do nothing to protect against babesiosis or tick-borne encephalitis.

Of course, if you’re halfway through a Big Trip, you may be days (or even weeks) from sivilization. The best advice in this case? Get to a doc as soon as you can. Then do as she tells you.

AREN’T THERE VACCINES?

It would be good to know that effective vaccines were readily available. But the only Lyme disease vaccine licensed for human use in the United States was withdrawn from the market in 2002. (If you’re a dog, however, you’re in luck. You have your choice of three. It’s a dog’s life, right?) There are also vaccines against Eurasian tick-borne encephalitis available in Canada and Europe, but none is licensed in the United States, and the value of these vaccines against Powassan virus is unknown. That’s unfortunate, since Powassan encephalitis kills one in ten afflicted individuals — older people would appear to be at greatest risk — with half of the survivors suffering severe, permanent neurological injury.

This makes rather grim reading, I admit. Perhaps you think I’ve exaggerated the risk posed by tick-borne diseases. And perhaps I have. It’s hard to know. At its best, the epidemiological data we have is spotty and unreliable. For instance, it’s estimated that the number of cases of Lyme disease reported to the CDC is only ten percent of the true number. Which means that, for now, the only useful rule of thumb is what I’ve sometimes called the “Fletcher Principle”:

IF IN DOUBT, DOUBT

Consider this: Our knowledge of the distribution of tick-borne pathogens in North America is far from complete, and statistics about the incidence of many tick-borne diseases in humans are little better. And as I said, appropriate vaccines are either hard to come by or nonexistent. So we have no choice: If in doubt, doubt.

Does this mean we should tread fearfully whenever we step foot away from the clear, well-trod path? Good question. For my part, I’m not ready to don a hazmat coverall when I leave the house. But I’m a lot more careful than I used to be. The climate clock is ticking, and it ticks for all of us.

This article was adapted from one originally published on 7 June 2016 at Paddling.net.


Further Reading

 

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