Lyme disease may not harm kids' brains.

Borrelia burgdorferi, the bacterium that causes Lyme disease, penetrates some people's brain tissue, where it can remain dormant for many years before causing cognitive disorders. That's one reason patients and physicians fear the illness.

In the first prospective study to look specifically for cognitive effects of Lyme disease in children, however, researchers came up empty-handed. None of the 41 youngsters examined suffered neuropsychological problems as a result of the infection, Wayne V. Adams and his colleagues at the Alfred I. duPont Institute in Wilmington, Del., report in the August PEDIATRICS. In 1993, the Centers for Disease Control and Prevention received almost 2,000 reports of Lyme disease in U.S. children.

In the study, the bacteria caused central nervous system disorders -- such as Bell's palsy -- in nine patients but no apparent cognitive ills.

However, the researchers administered neurological and cognitive tests only an average of 2 years after the patients became sick, and symptoms may take longer to develop, they acknowledge. As a result, the team continues to study the children. Also, these findings may not apply to anyone who did not receive treatment or received it too late.

In addition to the tests given to the participants, age 6 to 17, the researchers also compared the children's pre- and postdisease standardized achievement test scores.

Commenting on the study, pediatrician Ilona S. Szer of Children's Hospital and Health Center in San Diego cautions that "only in about 20 years can we be sure" that the bacteria left the children's brains unharmed. B. burgdorferi usually takes many years to cause noticeable damage, she argues.

Szer does find some comfort in the new results, however. The researchers employed very sensitive tests that should have picked up subtle changes that could precede obvious cognitive disturbances, she says.

In 1991, Szer and her colleagues reported on 36 children diagnosed with Lyme disease between 1972 and 1981 who had not received treatment until at least 4 years after symptoms began. By the late 1980s, only the two participants diagnosed with bacteria in their spinal fluid had cognitive difficulties, she says.

Studies reporting that infection with the Lyme disease bacterium leads to mental ills in treated and untreated adults aren't conclusive, Adams and his colleagues say. The studies' methodologies were sometimes weak, and researchers often selected patients with neuropsychological complaints.

Scientists have fingered a new carrier of b. burgdorferi: dogs. A new study demonstrates that a deer tick feeding on an infected canine will pick up the bacterium, Thomas N. Mather of the University of Rhode Island in Kingston and his colleagues report in the July 15 JOURNAL OF THE AMERICAN VETERINARY MEDICAL ASSOCIATION. The ticks can then infect humans, although the dogs themselves cannot. Not all dogs develop symptoms, Mather adds.