Disease Emergence...

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by Arno Karlen

Anchor Books, a Division of Random House, Inc., 2000

According to a recent CDC report, reported cases of Lyme disease (LD) in the U.S. have more than doubled over the last 25 years. Now officially the most common vector-borne disease in the U.S, the estimated 20,000 new cases each year are still only the tip of the iceberg.

Public health statistics may look impressive, but often are more of a best-guess snapshot than a definitive last word: Data out are only as good as data in, and gathering good data on LD is particularly fraught. Most cases go unreported (10 to 15 unreported cases for every one recorded - some say even more). Further complicating matters, the antibody-based test required for reporting is prone to false negatives. 

Also, LD is a “notifiable” disease, meaning that all cases should be reported to the CDC, but it is a voluntary system. Lab costs are borne by individual states, but many states don’t have adequate funding. Some states, where LD is known to be endemic, have decided there is little to be gained in practical terms from testing, so instead shift limited dollars to public awareness programs. In states where LD has not historically been a significant threat, a loopy logic takes hold: “There is no LD is the state because there has never been a case reported, so there is no need to test because there is no LD in the state.”

Adding yet another wrinkle are the tens of millions un- and under-insured Americans who are unlikely to see a doctor for something as seemingly trivial as a tick bite or joint pain - at least until the disease develops into its more difficult-to-diagnose-and-treat chronic form.

Nothing about LD is simple. As Arno Karlen meticulously documents in his fascinating book, “Biography of a Germ,” Borellia burdorferi (Bb), the bacterium behind a truly staggering range of symptoms (“wandering” rash, arthritis, meningitis, heart arrythmia, Bell’s palsy, and a variety-pack of neurological conditions clinically identical to several psychiatric disorders), is a remarkably versatile and hardy life-form.

For starters, it is a shape-shifter. Although most commonly thought of as a spirochete with a springy cork-screw silouette, Bb can also appear as a filament, a cyst, a granule, or as a hooked “elbow” rod. These “L” forms (named after the Lister Institute where they where discovered) not only help Bb hide out in body tissue, safe from the circulatory reach of macrophages and antibodies, they also make it difficult for antibiotic drugs to attack the structure of the bacterium’s cell wall. When stressed, Bb bacteria simply change form, tossing out anything requiring too much maintenance, including cell walls. But even in its stripped-down-to-the-bare-essentials incarnation as a mere granule, Bb can still infect.

Equally astonishing:  the variety of ways the germ can reproduce. There is, of the course, binary fission, where genes duplicate, a cell divides, and one becomes two. But Bb can also develop cyst-like structures from which fully formed spirochetes emerge. If that’s not alien enough for you, it can also grow branchlike filaments like plant that break off and turn into new spirochetes.

The weirdness doesn’t stop there. Like all vector-borne pathogens, Bb must negotiate life in a variety of radically different environments— inside ticks, mammals, and even birds—and it does so with disconcerting ease, armed with shifting surface proteins designed to confound any immune system it meets.

By the time Bb (actually, at least 4,000 Bb’s, which is what it takes to infect a human) make the final passage from tick to human, these tiny, sturdy, master-of-disguise travelers will have passed one or two winters in the bodies of dormant ticks and traveled miles of wooded trails in the bodies of white-footed mice, or rabbits or raccoons. They may have flown long distances either inside a migrating bird, or inside a tick clamped tightly to a migrating bird. At every turn, they have defied the odds, not only triumphing over host’ defenses, but also in their many hosts very survival. A cat that eats a mouse also eats whatever is in the mouse...

Remarkably, Bb manages all this with exactly one chromosome and fewer than 1,500 genes.

Karlen, always the conscientious biographer, follows his subject through every improbable plot twist and turn, from the oddly heroic intricacies of deer tick sex, to the decades-long effort to identify the pathogen, an effort riddled with missed opportunities and blinded by conventional wisdom: “The long lack of follow-up to (earlier) insights merits an entry in the annals of medical myopia.”

Still, there is some good news:

1) Bb cannot survive in mosquitoes

You can get all sorts of other nasty diseases from mosquitoes, so it’s still a good idea to use a repellent.

2) Due to basic tick mechanics, it takes several hours—Karlen suggests 24—for a tick to transmit enough Bb to infect a human.

But tick nymphs, about the size of the period at the end of this sentence, are the ones most likely to infect humans, and have a talent for getting into areas where they are hard to spot, such as hair. Regular tick checks when camping, running, hiking or simply living in tick-infested areas are a must. Tick nymphs are most plentiful in the Spring.

3) Bb is not found in the tropics.

But closely-related borrelias are found just about everywhere else, including Russia, China, Europe, Australia, North Africa, Japan and, of course, North America.

4) Most people who are infected are able to fight off the infection, often without  showing any sign of clinical symptoms.

This is true of most diseases. Researchers have no idea why some people get sick while others don’t. There are plenty of variables from the overall health and genetic make-up of the human host and the particular strain of Bb involved (there are hundreds) to what shape Bb assumes and co-infections. The very same ticks that carry Bb can also transmit other pathogens, including Babesia, a protozoan that causes malaria-like symptoms. It is even possible to become infected with multiple strains of Bb from a single tick bite. The number of circulating strains also explains why people who have been infected once and developed antibodies for a particular strain can be infected again, and why it has been so difficult to develop and market a vaccine.

Toward the end of the book, Karlen shifts focus from the micro to the macro, charting Bb’s global spread and its emergence over the last few decades as a major threat to human health. For the last hundred years, almost as soon as there were “bacteriologlists” to look, scientists began gathering clues about Bb’s existence. By the 1940s, it had been linked to a distinctive “bull’s eye” rash, suspected of being tick-borne and a spirochete, and had even been successfully treated with antibiotics in Europe.

But illnesses in the Old World were not linked to illnesses cropping up in the U.S. Also, blinded by the conventional wisdom of the day, scientists searched for Bb in the wrong type of tick: soft-shelled instead hard-shelled ticks. Bb’s “discovery” in 1970s had more to do with a chance finding by a researcher studying another ticke-borne disease, Rocky Mountain Spotted Fever, than to any concerted scientific effort. 

When and how Bb found its way to Lyme, Connecticut is still a matter of some debate, though clearly it was after that glaciers retreated about 13,000 years ago. Whether Bb spread into North America in tandem with human settlers from Asia crossing the Bering land bridge, or more recently via ticks on rats, cats or sheep on ships from Europe, there is little doubt it has been part of the local scenery for quite a while.

Bb’s fortunes have changed along with its habitat. In the two centuries following the Mayflower’s arrival in New England in 1620, forests were felled for farmland, and deer hunted to local extinction. Bb and its tick hosts retreated into whatever wilderness pockets they could. As the land became less productive, settlers moved westward, forests grew once again. Then deer were shipped in from the Midwest and new landscape of fields, woods, scrub and villages emerged.

“…Deer populations started rebounding in the early twentieth century, but predators such as wolves, bears and big cats did not. The recuperating land also had a resurgence of birds and small mammals. In 1938, when half of Connecticut was forest again, the WPA guide to the state said that no place in America offered better rabbit hunting, and again there were raccoons, foxes, muskrats, mink and otter.”

It would be hard to imagine a place offering more opportunity for a Bb-carrying tick. By the 1970s, when the promise of a simpler life and fresher air brought suburban sprawl to the woods, Bb was well-established and ready to take advantage. 

Still, from Bb’s perspective, humans are a waste of time, an “incidental host,” a dead end. An infected human rarely transmits enough bacteria to infect a tick. Deer are much better for that.

Since the discovery of Lyme Disease, Bb – or one of its many close relatives – has been found almost everywhere where anyone has looked. Different tick species may be involved, but the basic m.o. is the same. Given the volume of modern trade and travel, and how easily, for example, ticks on a dog in a car can sprint across a continent, no place is completely safe. There are also local variants, including Borrelia lonestari, which is carried by the lonestar tick common throughout the South. (Although the CDC recognizes a Lyme-like disease can be caused by a lonestar tick bite, the evidence is still thin for whether lonstari or another pathogen is the culprit.)

It is also critical to remember that Lyme Disease isn’t only a problem for humans, but also for dogs, horses, cows, rats, and any new susceptible host that presents itself, including exotic pets. 

So check yourself and your pets for ticks, pull socks over pant legs when hiking, no matter how dorky it looks, spritz a little DEET and, if you live near woods, use gravel or wood chips to create “tick moats” around buildings (they hate to walk on the stuff).

Then -- and only then -- will you feel safe enough to read Biography of Germ.

-  j.a. ginsburg