A rare disease that preys upon the spinal cord, resulting in muscular weakness and paralysis, has spread across the United States. The CDC has confirmed two cases of acute flaccid myelitis, or AFM, in New York City and six in New Jersey, with 116 total cases diagnosed across 31 states in 2018. According to CNN, 10 more cases have been added to the running tally in the past week alone.

AFM—billed as "polio-like" because of its deleterious effect on the nervous system—has been on the rise since 2014, peaking in the fall and mystifying researchers. AFM typically develops in the wake of an enterovirus (think: respiratory issues, fever), most often in children. But while most kids come out the other end perfectly fine, some begin to exhibit weakened muscles and reflexes about three to 10 days after the cold-like symptoms subside. AFM may also result in facial slackening and drooping eyelids, as well as difficulty speaking, swallowing, and even breathing.

AFM can come from poliovirus, but investigators have eliminated that suspect: Testing 440 patients' spinal fluid since 2014, they've found evidence of pathogens (none of them polio-related) in only four samples. The CDC does not yet know what's causing this disease, but of the 400-plus cases identified so far, over 90 percent have occurred in children.

In addition to the 116 confirmed diagnoses, 170 possible AFM cases are currently under investigation. AFM has tended to proliferate between August and October each year, correlating with the onset of cold and flu season, and spiking every two years since 2014 (so, 2014, 2016, and this year).

Neither New York nor New Jersey rank among the states with the highest number of AFM diagnoses—Colorado and Texas lead the pack, with 15 and 14 documented cases respectively—but the CDC urges parents and guardians of kids exhibiting symptoms to report to a doctor ASAP: The agency asks medical professionals' help in collecting information for their investigation. It has also convened a task force to get to the bottom of this mystery disease, and as CDC Director Robert Redfield, M.D., put it in a statement, "to actively detect, more effectively treat, and ultimately prevent AFM and its consequences."