Published 4:48 PM EDT Oct 19, 2018
Scientists are studying whether the rare but paralyzing illness that has afflicted scores of children this year is linked to a respiratory virus that circulates in late summer and early fall.
The Centers for Disease Control and Prevention this week reported 386 cases of acute flaccid myelitis since August 2014. The illness mainly strikes children.
Cases are exceedingly rare; fewer than one in a million children are affected. But for a small number of children, the results are devastating.
It can paralyze a child's arms and legs. Some who are stricken need ventilators to breathe. It can also cause muscle weakness, slurred speech and difficulty moving eyes and swallowing.
CDC officials have not identified what causes acute flaccid myelitis, or AFM. Although described as a polio-like illness, each confirmed case has tested negative for polio virus.
A strain of a respiratory virus called enterovirus has been detected in several cases, but federal health officials say they don't have enough evidence to conclude a single culprit is responsible for AFM.
They're also investigating whether genetic or environmental factors are involved, and how the body responds to the disease.
"This is a mystery so far and we haven’t solved it yet," said Nancy Messonnier, director of the CDC's National Center for Immunization and Respiratory Diseases.
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The illness peaks every other year from late summer through early fall. Public health officials began tracking it in 2014 with 120 cases in 34 states. There were fewer than two dozen cases in 2015, but the illness surged again in 2016, with 149 cases in 39 states.
So far this year, 62 cases are confirmed in 22 states and another 65 suspected cases are being investigated, according to the CDC.
Priya Duggal, a genetic researcher at the Johns Hopkins Bloomberg School of Public Health in Baltimore, is studying the illness.
"It seems to be cyclical – it's every two years," she said. "It’s pretty tragic to see these families and to talk to these parents and realize how much their lives have been upended."
Duggal's study of about 60 families compares the genetic profile of children and adults in families stricken with the illness. In some families, parents and siblings recovered quickly from minor cold-like symptoms while one child was paralyzed.
Duggal is looking for genetic clues to why some children are susceptible to the more severe effects of the disease.
Some researchers believe the illness may be linked to a strain of enterovirus called D68, which circulated widely in 2014 among children who went to hospitals with trouble breathing. The respiratory virus is spread through coughing, sneezing and unwashed hands.
Children's Hospital Colorado noticed that a subset of children infected with D68 outbreak in 2014 developed muscle weakness.
Since then, the hospital has been tracking both the D68 virus and acute flaccid myelitis.
"We have seen an every-other-year pattern in late summer to early fall of a surge in cases in acute flaccid myelitis," said Kevin Messacar, a pediatric infectious disease specialist at the hospital in Aurora. "It directly correlates with the time D68 has been circulating at our institution and reported by colleagues in other parts of the country."
Messacar suspects the number of cases is likely higher than the confirmed total. Health professionals are not required to notify authorities when they encounter a case; all reporting is voluntary.
To be confirmed as AFM, cases must meet a strict definition: Signs of a weak or flaccid limb confirmed by MRI images of a patient's spine.
If D68 continues to circulate every other year, Messacar said, public health authorities might need to develop a vaccine.
The worst cases "are unmistakable," Messacar said. "They are paralyzed children that are not moving and they don't get better."
Several states have reported cases of AFM this year. The Maryland Department of Health has confirmed six cases; the Minnesota Department of Health has confirmed seven, all in children under 10.
Jayne Griffith, an epidemiologist at the Minnesota Department of Health, said the afflicted typically develop the disease following a respiratory or stomach illness.
Griffith said it's often difficult to test for the virus in a timely manner because hospital lab tests are not sensitive enough to identify the disease.
"That specimen needs to go to a state lab for further" testing, she said. "There is a little bit of a lag time."
The CDC said several AFM cases showed the D68 strain as well as another enterovirus strain, A71. Other common cold viruses, such as the rhinovirus, also have been detected in some cases.
Mark Pallansch is director of the CDC's Division of Viral Diseases. He said disease investigators are being methodical to avoid overlooking any potential cause.
Among areas that need further investigation, Pallansch said, are how the body's immune system responds to the disease, and whether environmental toxins may play a role.
"We are keeping a very broad approach," Pallansch said. "Unless we have definitive data, we don’t want to rule out potential causes for this disease. We are tending to be inclusive until we have good evidence to exclude."