AFM cases not polio-like, says CDC

Acute flaccid myelitis (AFM), being referred to as a ‘polio-like condition’, has been tested negative for the polio virus, said the Centers for Disease Control and Prevention (CDC) of the United States.

Around 590 cases of AFM have been reported in the US between August 2014 and October 2019. Every two years, since 2014, the number of cases rose. This year, 22 cases have been reported with no deaths. In 2018 too no death was attributed to the disease, but after six months of onset of the disease, two patients died.

AFM is a neurological illness. As ‘flaccid’ suggests, it is a weakness or paralysis of the limbs. In case of myelitis, there’s inflammation of the spinal cord. 

“Acute flaccid myelitis (AFM) is a rare but serious condition. It affects the nervous system, specifically the area of the spinal cord called gray matter, which causes the muscles and reflexes in the body to become weak,” according to the CDC.

The symptoms of AFM, particularly, weakening of limbs, are similar to polio.

Cause unknown

While the exact hasn’t been identified, the CDC believes that some virus may be the behind it. “We think viruses, including enteroviruses, likely play a role in AFM. We don’t know why a small number of people develop AFM, while most others recover,” states the CDC.

Since 2014, more than 90 per cent of patients with AFM have 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.

These cases peak during August-October. “Many viruses commonly circulate between August and October, including enteroviruses (EV) and will be temporally associated with AFM. The CDC is working with national partners to understand the annual circulation of enteroviruses, including EV-D68, and what association it may have with AFM,” said the US health protection agency.

The large number of AFM cases identified in 2014 coincided with a national outbreak of a severe respiratory illness caused by D68 strain of enterovirus (EV-D68).

The EV-D68 storyline showed many similarities with poliovirus a century ago, stimulating discussion whether EV-D68 could be ascertaining itself as the “new polio”, found a paper  Enterovirus D68 — The New Polio? published in Frontiers in Microbiology  journal.

Polio virus is also one kind of enterovirus, but the CDC has repeatedly said tests have confirmed that none of the AFM cases found from 2014 were positive for poliovirus. Also, the US was declared polio free in 1979.

Fresh research

Of the 305 children who were reported to have been struck by the disease in 43 states between 2015 and 2017, 193 were confirmed and 25 were probable, according to a paper on incidence of AFM in the US that will be published in the November issue of Pediatrics. Of confirmed patients, 61 per cent were male, white race (53 per cent), and non-Hispanic ethnicity (35 per cent), with a median age of six years.

The average annual incidence was 0.71 per million paediatric population.  In 45 per cent cases, three or four limbs were affected, while the rest had one or two affected. This paper too said the onset of limb weakness peaked between August and November, as CDC data suggested. 

Though EVs are likely to be the cause but important knowledge gaps exist, read the paper. “We conclude that symptoms of a viral syndrome within the week before limb weakness, detection of viral pathogens from sterile and nonsterile sites from almost half of patients, and seasonality of AFM incidence, particularly during the 2016 peak year, strongly suggest a viral etiology, including EVs,” according to the AFM paper.

“Although a temporal association between EV-D68 and AFM has been reported, additional evidence is still needed to more clearly establish a causal association. Additional studies are needed to assess risk factors, establish causality and develop a more comprehensive understanding of the mechanisms that lead to AFM,” it added.

India and AFM

While in the US, the incidence rate of AFM is 0.71 per million, in India it was 120 per million population in 2010 (the paper says it is 12 per 100,000 population), according to a paper authored by paediatrician Jacob Puliyel and others, published last year.

The authors had suggested that the incidence of non-polio AFM had increased over a period of years after India was declared polio free. They had attributed it to increased number of polio rounds.

The particular polio vaccine had five times more the live virus than the ones used earlier. This was a live vaccine, which, the authors said, were settling in the gut and causing non-polio AFM.

“Whether it is polio or not, the children are affected with paralysis. The complications are no less even if it is non-polio and they can’t be taken lightly,” Puliyel told Down To Earth.

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