New test homes in on evasive Lyme disease.

New test homes in on evasive Lyme disease 

A powerful laboratory technique frequently used in basic research reliably identifies trace amounts of DNA from the spiral-shaped microorganism that causes Lyme disease, according to government scientists. The finding should help researchers develop a diagnostic test for this elusive disorder, and may help unlock the mechanism underlying the disease.

Lyme disease gets its name from the Connecticut town where researchers first investigated a cluster of adults and children who suffered periodic bouts of flu, arthritis and neurological problems. Physicians now recognize these as classic symptoms of Lyme disease, caused by Borrelia burgdorferi bacteria (SN: 3/25/89, p.184). Yet doctors still have trouble confirming the diagnosis. At present they must rely on blood tests to detect antibodies to B. burgdorferi -- an unreliable method because some infected people display few, if any, such antibodies.

Patricia A. Rosa and Tom G. Schwan of Rocky Mountain Laboratories in Hamilton, Mont. (part of the National Institute of Allergy and Infectious Diseases) used a technique called polymerase chain reaction (PCR) to develop a test so sensitive that it can detect B. burgdorferi DNA in a sample containing as few as five spirochetes. That sensitivity is important because many Lyme patients have very few spirochetes in their blood or tissues.

The team first identified a target DNA sequence present in B. burgdorferi and then devised two DNA segments that home in on and bind with the target DNA. Adding the enzyme polymerase, which copies the original DNA target, prompts a chain reaction that generates millions of copies of the target, revealing the presence of spirochetes even in samples containing trace amounts of genetic material.

The scientists report in the December JOURNAL OF INFECTIOUS DISEASES that the PCR test picks out DNA from slightly different strains of B. burgdorferi. The test reacted with 17 of 18 strains tested -- a significant finding because many people infected with a slightly unusual strain slip through current diagnostic tests, Rosa says. The PCR test proved highly specific, reacting only with material from B. burgdorferi and not with DNA taken from a close relative known as B. hermsii, which causes a disease called relapsing fever.

A number of researchers already are applying these results in a race to develop a commercial PCR test for Lyme disease. That effort will take at least six months, estimates W. John Martin of the University of Southern California Medical Center in Los Angeles.

Rosa and Schwan plan to use PCR to find out why some Lyme patients develop severe complications such as neurologic and heart problems. One theory suggests those problems result because the bacterium changes to a form the immune system cannot recognize. Another theory holds that the heart and nerve damage comes from an autoimmune process triggered after the immune system conquers the initial infection. PCR would show whether patients with late-stage Lyme disease still harbor any form of B. burgdorferi, Rosa says.