The illness first attacks the nerve cells in the spinal cord that carry messages to muscles in the legs and arms. It shuts down the signals in these motor neurons, causing the muscles to wither. ALS, also known as Lou Gehrig's disease, typically results in respiratory failure. Death usually occurs 2 to 5 years after symptoms begin. The viral particles showed up in spinal tissue from only 1 of 29 people who died of other neurological diseases.
Echoviruses belong to the enterovirus family.
This group includes the polio virus, which also kills motor neurons. The disease damages neurons so badly that they are hard to identify in postmortem tissue. Judging from their size and shape, the cells containing fragments of echovirus RNA in the new study were clearly neurons, says study coauthor Martina M. Berger, a microbiologist currently at the University of California, Irvine. She adds, however, that it's impossible to be certain the cells were motor neurons. Berger and her colleagues detected the viral particles in the tissue by using a chain reaction that copies small portions of viral RNA millions of times.