Maximum likelihood phylogenetic trees of enterovirus species A, B, C, D and rhinovirus A, B, or C isolates from Latin America: The 5'UTR region is much more affected by recombination events than the VP4/VP2 coding sequence. Polio is in the enterovirus C species; enterovirus 71, a strain of enterovirus A, has been reported to cause rare neurological complications; the suspected cause of the 2014 cases is a strain of enterovirus D. Most enteroviruses and rhinoviruses cause only common cold symptoms. , the U.S. CDC regarded the cause of AFM as having "a variety of possible causes such as viruses, environmental toxins, and genetic disorders", listing poliovirus, nonpolio enteroviruses, West Nile virus, and adenoviruses among the potential causes. More than 90% of people with AFM reported having symptoms consistent with a mild viral infection before the onset of AFM. Much research has focused on the nonpolio enteroviruses 68 (EV-D68) and 71 (EV-A71), a common cause of hand, foot, and mouth disease in infants and young children, members of the enterovirus D and enterovirus A species, respectively, as suspected causes. Some evidence supports a causal role of EV-D68. Coxsackievirus A16 may also play a role in some cases. A 2014 Morbidity and Mortality Weekly Report report noted the difficulty of establishing causation by the virus. Avindra Nath, clinical director of the National Institute of Neurological Disorders and Stroke and president of the International Society for NeuroVirology, compared the situation to the prolonged investigations that led to confirmation of HIV as the cause of AIDS. In response to the suggestion that the enterovirus might be taking over the role of polio, Nath said that EV-D68 was far less virulent and spread much more slowly than polio, and that unlike in polio, only a few cases of paralysis were seen per thousand children infected. He also suggested that adults with respiratory diseases should also be evaluated for neurological deficits, and that infectious disease should be considered as a cause when patients presented with neurological symptoms. A subsequent report described 29 cases of EV-D68-associated AFM in Europe in 2016, noting, "these probably represent only the tip of the iceberg."
Acute flaccid myelitis
Vascular myelopathy
CMV polyradiculomyelopathy
Guillain–Barré syndrome
Subacute combined degeneration of spinal cord
Paraneoplastic cerebellar degeneration
Transverse myelitis
Amyotrophic lateral sclerosis