But its devastating legacy lives on in the mysterious affliction known as post-polio syndrome, in which the debilitating and paralytic effects of the quixotic virus return after decades of latency.

Next week, a group of top researchers will reveal what is known and what questions remain in a symposium at Scripps Memorial Hospital in La Jolla. The free event, open to the public, is aimed at polio survivors and their families, local physicians and health-care workers.

From a purely statistical standpoint, polio - which most often struck children - did not seem so menacing. In 90 percent of those contracting polio, the virus merely caused flu-like symptoms, if noticed at all. About 10 percent of those infected suffered high fever, meningitis (inflammation of membranes surrounding the brain and spinal cord) and severe neck and back pain.

But in about 1 in 100, the virus attacked nerves within the spine that send messages to muscles, resulting in partial or complete paralysis. With bulbar polio, the virus got into the brain stem. Muscles needed for vital functions such as breathing and swallowing became paralyzed, sometimes causing death. After months or years of physical therapy, many paralytic polio victims regained all or most of their motor function. These individuals commonly went on to active lives and careers.

But since the late 1800s, it has been known that polio survivors could develop new muscle weakness many years after contracting the disease. Those likely to be affected often had physically demanding jobs, suggesting overuse of muscles or susceptibility to some new spino-muscular affliction, like Lou Gehrig's Disease.

In the 1980s, 30 to 40 years after the main polio epidemics in the United States, the numbers of survivors complaining of renewed muscle weakness, fatigue, breathing difficulties and other such signs skyrocketed. By then, however, the majority of physicians had no experience with polio because it had been eradicated decades earlier. Diagnosing post-polio syndrome is difficult in any case - there is no test for it; the diagnosis is a process of elimination.

Cause questioned

Studies have identified 600,000 polio survivors in this country, but nobody knows how many suffer from post-polio syndrome, whose cause is not clear. The polio virus infects about 95 percent of motor neurons in the spinal cord and many nerve cells in the brain. Motor neurons, which control muscle movement, are connected to the muscles by long tentacles called axons, which carry signals commanding muscles to contract. Once infected, the cells either defeat the virus or die.

New axon sprouts are formed by the motor neurons that survive. Because of these new axon sprouts, surviving motor neurons that once controlled 1,000 muscle cells might now control 5,000 or 10,000 muscle cells. These powerhouse neurons allowed many polio victims to overcome paralysis. But what happens over time?

The leading hypothesis is these overburdened motor neurons degenerate, leading to a breakdown between the signal from the brain and the response of the muscle.

Sam Pfaff, assistant professor of developmental neurobiology at The Salk Institute, is trying to figure out at the molecular level how neurons are created and develop, and how neuronal signals move through the body. Besides post-polio syndrome, Pfaff's research could aid victims of spinal injuries, Lou Gehrig's disease, Parkinson's disease, multiple sclerosis and other neurological disorders. Pfaff's talk at the La Jolla symposium is titled, "Using Secrets of Embryonic Development to Treat Disease."

Another question facing post-polio researchers is the nature of the virus itself. Do polio and related viruses lay dormant in the body for many years and then re-awaken? If so, what causes their renewal? What effect might this have on disease?

Dr. J. Lindsay Whitton, a medical doctor and professor of neuropharmacology at Scripp's Research Institute, will explore virus behavior in his talk, "Persistent Virus Infection and Post-Polio Syndrome."

On the treatment side, rehabilitation techniques developed recently can stabilize or even reverse the effects of post-polio syndrome. Dr. Susan Perlman, associate clinical professor of neurology and director of the Post-Polio Clinic at UCLA, will speak on "Recent Advances in Treating Post-Polio Syndrome."

Dr. Anne Gawne, a medical doctor and specialist in physical medicine and rehabilitation, has treated post-polio patients for more than 10 years, both at National Rehabilitation Hospital and Roosevelt Institute at Warm Springs, Ga. Gawne, who has written many articles and book chapters on the subject, will discuss, "Exercise Including Aquatic Therapy" at the symposium.

Copyright 2002 Union-Tribune Publishing Co.