Using antibiotics for two to four weeks is enough totreat Lyme disease and there is no compelling evidence that longer treatments help, U.S. neurologists said Wednesday in releasing new guidelines.

Lyme disease is an infectious disease caused by tick-borne bacteria. The first sign is often a circular rash surrounding the spot where a tick bit you, which may be followed by symptoms like headache, fatigue and chills.

The Public Health Agency of Canadaestimates about 10 per cent of blacklegged ticks in an infected area carry the Borrelia burgdorferibacteria that cause Lyme disease. In the past few years, Lyme disease has spread to much of Ontario, southern British Columbia, New Brunswick, Newfoundland and Labrador, and Nova Scotia.

Left untreated, the disease can progress to a second phase that lasts several months.Symptoms may includemigraine, weakness, multiple skin rashes, painful or stiff joints, abnormal heartbeat and extreme fatigue.

The nervous system is affected in about 10 to 15 per cent of infected patients, according to the American Academy of Neurology.

"While other guidelines exist to help diagnose and treat general Lyme disease, there continues to be considerable controversy and uncertainty about the best approach to treating neuroborreliosis, in which Lyme disease involves the nervous system," said Dr. John Halperin, lead author of the new guidelines.

The authors analyzedscientific studiesto prepare the guidelines, which appear in the journal Neurology, the academy's official journal.

While some doctors recommend weeks or even months of antibiotics to prevent long-term complications, "there is no compelling evidence that prolonged treatment with antibiotics has any beneficial effect in post-Lyme syndrome," the guidelines said.

Rather, the nervous system infectionresponds well to two to four weeks of antibiotics such as penicillin, ceftriaxone, cefotaxime and doxycycline in both children and adults.

Long-term use of antibiotics does not improve outcomes for people with chronic symptoms, does not improve overall quality of life, memory or depression, the group said.

Long-term side-effects of antibiotic use may include diarrhea, blood stream infections, and blood clots.