A mysterious illness that has caused polio-like paralysis in at least 20 California children -- including half a dozen or so in the greater Bay Area -- does not appear to be widespread or pose a significant threat to other families.
In fact, doctors can’t yet say for sure that all of the cases are even the same disease. But doctors and public health officials who are eager to find the source of the illness said there may be other patients who have not yet been identified.
The illness is not polio. All of the children identified so far had been vaccinated, and none of them tested positive for the virus that causes polio. But, like polio, their illness causes sudden paralysis in at least one limb, and so far the children have recovered very little strength or motor function since they first became sick.
The first signs of the illness emerged in late 2012 in patients who were treated at Stanford and UCSF. Those cases and three others were described in a report released Monday, but doctors have found at least 15 other patients.
The most likely cause of illness is a virus, doctors say. They noted that there are no signs that the virus is in wide circulation and they do not expect to see a surge in similar cases. Nonetheless, there may be more cases out there, and public health officials want doctors to be looking out for children who experience sudden paralysis without an obvious cause.
’’We don’t have the impression that there’s any real threat. We don’t see an escalation of cases,” said Dr. Emmanuelle Waubant, a UCSF neurologist who helped write the report describing the first few cases of the mystery illness.
There are far more questions than answers around the illness. Investigators found a rare virus called enterovirus-68 in the nasal passages of two of five children whose illness has been thoroughly studied, but they couldn’t find evidence of that virus in the other three patients.
There are several dozen strains of enterovirus -- including the strain that causes polio, plus a strain that has been associated with polio-like illness in Asia and Australia.
Enteroviruses aren’t rare, but they also aren’t usually very serious. For example, up to 90 percent of unvaccinated people who are infected with the polio virus will experience no symptoms. Less than 1 percent of them will suffer paralysis from polio, and up to 10 percent of those patients die when the paralysis reaches the muscles that help them breathe.
Polio was common in the United States until 1955, when the vaccine was made available. It’s been eradicated in the United States since the 1970s, and because of global immunization efforts, the disease is widespread in only three countries now.
But every few years outbreaks of polio-like illness appear in pockets around the world, including the United States.
Among the new cases in California, “there is no clustering whatsoever,” said Dr. Keith Van Haren, a pediatric neurologist at Stanford’s Packard Children’s Hospital who studied the first cases with Waubant.
None of the children he’s looked at so far have had any contact with one another, he said. If a virus is indeed the cause, it is likely able to spread from person to person, but the paralysis “is a very rare manifestation” of disease, he said.
It’s been difficult to isolate the cause of their illness because most of the children aren’t seeing specialists until weeks, if not months, after their symptoms began. In several of the cases, the children first had what seemed like a minor respiratory illness -- a basic cold -- that became more serious. Then, the children lost control of a limb.
’’Vikash had a sore throat, a fever, and he seemed to get over it. But a couple of days later he complained that his shoulder hurt, and all of a sudden he couldn’t move his left arm,” said San Jose resident Nirupa Muruhathasan, whose son, now 10, got sick in September 2012.
The entire family, including Vikash’s brother, was sick at the same time, but Vikash is the only one who suffered paralysis. His mother said physical therapy has helped, and Vikash, who’s left-handed, has regained some fine motor skills and is able to write and grip things with that hand. But the arm is still very weak and he has trouble lifting or moving it.
’’I just want to be hopeful and keep trying,” Muruhathasan said. “Kids are very resilient, and they don’t have enough history or data for this illness to predict what will happen three or four years down the road.”
Vikash eventually was tested for enterovirus-68, but that was months after he’d been sick and no trace of the virus was found, his mother said. By the time he saw Waubant at UCSF, Vikash had been diagnosed with, and received treatment for, an autoimmune disease, but his doctors no longer believe that was the cause of his paralysis.
Because most modern doctors have never seen a case of polio, or even polio-like illness, most of the children initially were diagnosed with other conditions that can cause paralysis. Many were treated with steroids or other therapies that can make testing for a virus difficult.
Waubant and Van Haren hope that by making public the cases they’ve seen so far, they can alert doctors to look for patients early in the disease progression. That may improve treatment, and it could help scientists discover or confirm what’s causing the illness.
“We’re doing our best not to alarm people,” Waubant said. “What we’re trying to do is work with everyone in the community to identify patients early in the course of the disease.”