The exact cause of AFM has not been determined. But in the study published in Nature, scientists discovered immune reactions to two types of enterovirus in 70% of fluid samples from children with AFM. These reactions appeared in only 6% of samples from a control group of children with neurological conditions other than AFM.
Specifically, the study identified antibodies for enterovirus strains D68 and A71.
Enterovirus D68 (EV-D68) caused a nationwide outbreak from Aug. 2014 to Jan. 2015, according to the CDC. During this outbreak, the virus sickened 1,153 people in 49 states and the District of Columbia.
What Is Acute Flaccid Myelitis?
Acute flaccid myelitis is an extremely rare condition of the nervous system that causes the muscles and reflexes of the body to weaken, the CDC says. It may be spread to humans by mosquitoes, but people cannot spread AFM.
AFM symptoms include a sudden onset of arm or leg weakness and loss of muscle tone and reflexes, according to the CDC. Other symptoms can include facial droop, eyelid droop, difficulty moving the eyes, facial weakness, slurred speech, or problems with swallowing. The most serious potential symptom is respiratory failure.
Lab tests are required to diagnose AFM. The CDC says the rare condition occurs in less than one in a million people in the United States every year.
The agency says scientists have proposed a variety of causes of AFM, including viruses, but also environmental toxins and genetic disorders.
What Is Enterovirus?
Enterovirus infections are extremely common. They belong to the family of RNA viruses, according to Charles Patrick Davis, MD, PhD. He said most people infected with enteroviruses have mild symptoms or none at all. Why some of these cases develop into AFM is unknown.
Unlike AFM itself, enterovirus infections are highly contagious, Dr. Davis said. Even if they do not develop AFM, people infected with enterovirus may nonetheless experience significant health symptoms:
- Common cold: nasal discharge, cough, mild fever, mild malaise
- Hypoxia (low oxygen in the blood): shortness of breath, wheezing, coughing, rapid breathing, skin coloration change (bluish to cherry red), rapid heart rate
- Aseptic meningitis: most common among infants and children; may also occur with a rash (on face, neck, and extremities), fever, painful headache, stiff neck, body aches, sensitivity to light, nausea and vomiting, irritability
- Conjunctivitis (hemorrhagic): eye pain, bleeding seen in the whites of the eyes, photophobia (avoidance of light due to discomfort)
- Myopericarditis: shortness of breath, chest pain, fever, weakness
- Herpangina: small flat sores on the oral mucosa (tonsils and soft palate) that may produce blisters and ulcerate
- Pleurodynia: intermittent chest pain usually over the lower part of the rib cage; some individuals may have a plural friction rub that can be heard when the doctor examines the chest with a stethoscope
- Hand, foot, and mouth disease (HFMD): small nodules and blisters that are tender and appear gray that occur on the hands, feet, and in the oral cavity
- Encephalitis: Symptoms range from lethargy and drowsiness to personality changes, seizures, and coma.