Patients suffering from the disease quickly and permanently become paralyzed in one leg or arm, and others have lost use of up to all four extremities. Some patients have respiratory symptoms before the paralysis begins, said Dr. Keith Van Haren, a Lucile Packard Children's Hospital pediatric neurologist.
"We suspect it is a virus," but doctors have not yet confirmed its presence in all of the patients, he said.
Van Haren and Dr. Emmanuelle Waubant, professor of neurology at the University of California San Francisco, are researching the cases and have found a virus, enterovirus-68, in the nasal swabs of two patients, but that sample is too small to draw conclusions, Waubant said. Enterovirus-68 is in the same family as the polio virus.
The polio vaccine does not protect against enterovirus-68 and there is no evidence that the vaccine causes the disease. Doctors stressed the disease is rare. It is occasionally seen in the Bay Area, but the presence of five cases in the past 18 months is unusual, Van Haren said.
Other enteroviruses can cause similar symptoms. Another strain, enterovirus-71, has been implicated in similar cases of acute flaccid paralysis in Southeast Asia and Australia, but that strain is not known here, Van Haren said. The cases, which began in September 2012, have ranged in location from Monterey County to the North Bay, with others in southern California. There are no confirmed cases outside California.
Most of those stricken are ages 2 to 16 but the disease has affected some adults, Van Haren said.
In some cases, the paralysis is preceded by a respiratory infection. In other cases, sudden muscle weakness rapidly progresses to flaccid paralysis, where the limb hangs and cannot move.
"All of the children have permanent weakness," Van Haren said. "So far, we've seen modest to very little recovery."
But parents should not panic if their child drops a toy. The weakness will be much more apparent and sudden. Any weakness that lasts for a few hours should be immediately looked at by a physician, the doctors said.
But in most cases, the virus won't progress to paralysis, they said.
"We think it's a very small number of patients infected with this virus who will have the neurological condition," Waubant said.
One case investigated at Lucile Packard involved a Berkeley girl, Sofia Jarvis, who is now 4 years old. In November 2012, Sofia, then 2, suffered from a respiratory infection and severe wheezing. Her parents took her to the doctor, and she was treated with Albuterol, an inhaler medicine that opens airways, her mother, Jessica Tomei, said. On the way home, Sofia started vomiting.
She was admitted to the hospital with breathing distress, Doctors thought she had asthma, her mother said. After four days, she returned home. The next day, she returned to her pediatrician for a follow-up appointment, as the doctor did not rule out pneumonia.
After the visit, Sofia reached into the treasure box in the family's waiting room.
"I saw her left hand in mid-grasp stop working," Tomei said. "Over three days, she was not using her left arm."
Sofia's parents, Tomei and father Jeff Jarvis, said they spoke publicly to alert other parents about what happened to their daughter.
"I know we are so lucky that she is here, and she is going to do amazing things," Tomei said.
Sofia calls her dangling arm "Lefty." It's a way to keep the arm integrated with the rest of her body as she tries to regain some movement, Tomei said.
A lively girl with wavy red hair, the disease has not affected her mentally, her mother said. She loves to dance, attends a Montessori preschool and is still academically advanced for her age. But she must learn alternative ways to dress herself and tie her shoes, Tomei said. She is currently physical and occupational therapy.
Van Haren and Waubant will present their findings at the American Academy of Neurology's annual meeting, held in Philadelphia, Penn., April 26 to May 3. The California Department of Public Health is also tracking the cases.