W A S H I N G T O N, July 5, 2001 -- It's been a cool wet spring in the Northeast, but as the weather improves, more and more people are heading out to the woods and fields, and more and more of them are worried about Lyme disease.

According to the Centers for Disease Control, this nasty by-product of the bite of the deer tick is America's fastest-growing vector-borne disease, one carried by birds, animals or insects. Much of the impact has been concentrated in the areas of New York and Connecticut north and east of New York City.

No one doubts that Lyme disease is serious business &151; painful and debilitating — but there is serious debate about how long Lyme disease can last. Some long-established physicians are facing discipline from their state medical board for what they and some of their patients call effective treatment.

The accepted medical opinion is that Lyme disease never lasts beyond 30 days. Among those most eager to accept this definition are America's health insurers, in order to limit their liabilities. In one letter cited in tonight's report, one major health insurance company promises to seek discipline against doctors who diagnose and treat "chronic" Lyme disease. No matter that many patients insist the lingering illness, which can be both physically and psychologically disabling, is continuous with their originally diagnosed Lyme disease; no matter that the constellations of symptoms of both 30-day and "long-term" Lyme disease certainly overlap — most medical texts insist the late-lasting symptoms are the product of something else and not Lyme disease.

Sharpening the dispute is the treatment frequently prescribed for chronic Lyme disease: a lot of antibiotics for a long time. Many of these treatments can go on for years, completely contrary to one of the Ten Commandments of today's medical correctness: preserve the effectiveness of all antibiotics by using each of them sparingly.

Finally there is the matter of cost. Whether borne by the patient, the insurer or taxpayers, the bill for treating chronic Lyme disease can be enormous. Treatment can cost as much as $70,000 — "as much as a case of AIDS," notes one of the embattled doctors who believes in the long-term disease.

With those stakes, it is perhaps not surprising that this medical disagreement has gotten nasty. Working physicians are facing challenges to their credentials and careers for persisting in treatments the medical authorities think bogus, even if some patients insist they work.

Dave Marash is a correspondent for Nightline.