Causes of AFM

  • We think viruses, including enteroviruses, play a role in causing AFM.
  • All the stool specimens from AFM patients that we received tested negative for poliovirus.

Possible Causes of AFM

Our five years of surveillance data have contributed important evidence to support the role of viruses, including enteroviruses, in AFM.

Most patients had respiratory illness or fever

  • More than 90% of patients with AFM had a mild respiratory illness or fever consistent with a viral infection before they developed AFM.
  • Respiratory illnesses and fever from viral infections such as from enteroviruses are common, especially in children, and most people recover. Enteroviruses can also cause neurologic illness, such as meningitis, encephalitis, and acute flaccid limb weakness, but these are rare.
  • We don’t know why a small number of people with enterovirus infection develop AFM, while most others recover.
  • We are continuing to investigate possible ways that people develop AFM including:
    • Direct virus infection of the motor neurons (nerves that make the muscles move)
    • Indirect infection where a virus may lead to an inflammatory or immune response directed toward motor neurons
    • Host genetic factors in which certain children may be more susceptible than others

Increase in cases between August and November

  • Most patients had onset of AFM between August and November, with increases in AFM cases every other year starting in 2014.
  • Many viruses, including enteroviruses, commonly circulate between August and November, at the same time that AFM outbreaks have occurred. CDC is working with national partners to understand the annual circulation of enteroviruses, including EV-D68, and their association with AFM.
  • The 2014 AFM outbreak coincided with a national outbreak of severe respiratory illness caused by EV-D68. EV-D68 outbreaks have also been detected in 2016 and 2018.

Detecting the causes of AFM

CDC has tested many different specimens from AFM patients for a wide range of pathogens (germs) that can cause AFM.

  • We have detected coxsackievirus A16, EV-A71, and EV-D68 in the spinal fluid of a small number of patients with AFM, which points to the cause of their AFM. For all other patients, no pathogen (germ) has been detected in spinal fluid to confirm a cause.
  • Studies have shown that AFM patients had antibodies specific for enteroviruses in their spinal fluid more often than persons without AFM. Having antibodies for enterovirus means that a person was previously infected with the virus.
  • All the stool specimens from AFM patients that we received tested negative for poliovirus.

Often, despite extensive testing of AFM patients, no pathogens are found in the spinal fluid. This may be because the body has cleared the pathogen, or it is hiding in tissues that make it difficult to detect. Another possibility is that the pathogen triggers an immune response in the body that causes damage to the spinal cord.