Mikell Sheehan thought her seven-year-old daughter, Bailey, had a terrible cold. But eight days and eight doctor’s visits later, Bailey was paralyzed on her right side, in what would turn out to be one the first surges of a syndrome called acute flaccid myelitis (AFM) in 2014.
Since then, 500 children across the United States have fallen ill with the little-understood paralyzing disease, with upticks happening every other year. In 2018, 158 cases were diagnosed, the largest number to date.
Now, after the most recent surge, physicians across the US are working to understand what causes the paralysis before another potential outbreak in the late summer and early fall of 2019. But so far they have not come up with a definite answer.
“It was infuriating, you go to the doctor and you think you’re going to get answers and you’re going to get a treatment and it will get better,” said Mikell Sheehan. “The doctors were telling us they didn’t know what it was.”
Bailey is 11 now and receives 45 minutes of physical therapy daily, which was developed from regimens used in polio victims. She regained the ability to walk. Mikell called Bailey “one of the lucky kids”.
Children with AFM often start out with a cold, which develops into the rapid onset of weakness and paralysis in the face and limbs. In the most severe cases, children are placed on ventilators as weakness develops in muscles used to breathe.
There is no treatment to stop the onset of paralysis, and no way to prevent the disease. Even testing for what researchers believe is the most likely culprit is limited to a select set of specialized labs. The disease appears to be occurring seasonally across the US, in 36 states, in the late summer and early fall, in every-other-year cycles researchers are struggling to explain.
“AFM is spiking now, but before it was rare – very, very rare,” said Keith Van Haren, assistant professor of neurology and pediatrics at Stanford University in California. “Something changed in that time around 2012, and now we’re having it every year.”
A leading hypothesis about the surge in AFM is a recent uptick in infections by an enterovirus called EV-D68. Enteroviruses are part of a large class of small viruses, so named because they often live in people’s guts (entero). The CDC has identified more than 100 enteroviruses.
The viruses have some defining characteristics. They typically occur seasonally, in the later summer and early fall in temperate climates; they evolve significantly over time; and they usually cause mild infections with cold-like symptoms.
The best known enterovirus is polio, which also causes paralysis. Polio has been nearly eradicated worldwide. Just 22 cases were reported in 2017, according to the World Health Organization.
EV-D68 was first identified in California in 1962. Van Haren believes the recent outbreak of AFM is probably attributable to a new strain that developed as the virus evolved over time.
“The modern strains of EV-D68 have developed the capacity to infect a specific part of the nervous system, and that is the part of the nervous system that supplies muscle control to the muscles and nerves,” he said.
One of the earliest surges struck Colorado in 2014.
“A previously uncommon virus – enterovirus D68 – was the cause of the respiratory cases we were seeing during that season,” said Kevin Messacar, professor of pediatrics and infectious diseases at Children’s Hospital Colorado. “Our entire hospital was full [with] many kids with and without asthma who were presenting with the symptoms of asthma.
“It was in the middle of that we found a number of children presenting with weakness in the arms and legs and with very unusual imaging of their spinal cords,” said Messacar. Children are typically tested for AFM with MRI or other imaging and reflex tests.
Other countries have also seen surges in EV-D68 infections. One leading researcher said the phenomenon was most pronounced in the US but that EV-D68 was circulating worldwide and often undiagnosed.
“We do know the virus has been following a similar pattern in Europe,” said Bert Niesters, a professor of medical microbiology at the University of Groningen in the Netherlands. “It was there in 2014, there in 2016, and there is some early evidence that it has been circulating again in 2018.”
There is still variability in the causes of AFM. In 2018, Messacar discovered nine cases of AFM were linked to a second enterovirus, called A71, which is best known for causing hand, foot, and mouth disease outbreaks in Asia.
“There are cases that are probably not attributable to EV-D68. We know that’s the case,” Van Haren said. Still, he said, EV-D68 was the most likely culprit in most cases, and one he believed the CDC had been slow to address as the debate over the exact cause of AFM plays out.
“If we wait until everyone is sure, and it’s 100% certain, you’ve waited too long,” Van Haren said.
Nancy Messonnier, director of the center for immunization and respiratory diseases at the US Centers for Disease Control and Prevention, said the agency was “trying to systematically pursue all those lines of reasoning”. Should researchers pursue EV-D68 only, finding ways to prevent and treat infection might remain “less than satisfying”, she said.
Studies are looking to characterize AFM’s specific symptoms, find whether there is genetic vulnerability to the disease, and see whether the virus can be found in fluids such as blood or spinal fluids.
“We’re trying to be broad-minded in our hypotheses,” said Messonnier. She called the connection to EV-D68 a “leading hypothesis – it’s not the only hypothesis”.