GPs called to help track down dangerous polio-like viruses

Doug Hendrie

11/11/2020 2:55:48 PM

Is polio over? Not yet, with polio-like enteroviruses on the rise and vaccine-derived poliovirus seeing a resurgence overseas.

Illustration of acute flaccid myelitis
The D68 strain of NPEV poses risks due to its links to acute flaccid myelitis (AFM).

GPs have been called to be on the lookout for new non-polio enteroviruses (NPEV) that can cause acute flaccid paralysis, or even death.
Four children died in a 2013 outbreak of the A71 enterovirus strain in Sydney, which can circulate in mild form and cause hand, foot and mouth disease. More than 100 others had severe neurological issues.  
Meanwhile, a worldwide rise in cases of circulating vaccine-derived poliovirus has led to researchers calling for a continued focus on maintaining Australia’s high rates of polio vaccination.
Researchers are concerned about the A71 and the D68 strains of NPEV, in particular, both of which can manifest in mild forms as the hand, foot and mouth disease that commonly affects young children.
The D68 poses risks due to its links to a newly recognised condition, acute flaccid myelitis (AFM), with a recent Communicable Diseases Intelligence bulletin warning of ‘growing evidence of a causal link between AFM and outbreaks of non-polio enterovirus species, in particular enterovirus D68’.
New research in the Journal of Paediatrics and Child Health calls for increased awareness and vigilance for these NPEV due to the challenges to identification and the risks to public health.  
The research suggests doctors should request stool samples in suspected cases of acute flaccid paralysis (AFP) and inform the Paediatric Active Enhanced Disease Surveillance Network and the Australian Paediatric Surveillance Unit.
The samples are necessary to differentiate enterovirus-linked AFP from those linked to the more common Guillain-Barre syndrome. 
Research co-author and paediatric infectious diseases physician Dr Phillip Britton told newsGP the new enteroviruses are cropping up through poliovirus surveillance programs.
‘These two strains, A71 and D68, have caused problems in North America and East Asia over the last 15 years,’ he said. ‘That’s why reporting cases of polio-like illness in children is really important. Sending specimens as early as possible to reference labs to test for these is often overlooked. 
‘From a GP perspective, it might come to your attention from hand, foot and mouth, fever and rash in young children. If there was a cluster in your area, sending a swab to reference labs to find out what viruses are around could be worthwhile.’ 
Dr Britton says NPEV can lead to permanent injuries.
‘There are several from the 2013 outbreak left with permanent spinal cord injury with long-term sequelae of paralysis, and several who had similar long-term consequences from the D68,’ he said.
‘It can be quite a devastating illness, and very much like polio in the ’50s and ’60s.’
In better news, the NPEV strains do not appear to be as infectious as poliovirus, which led to mass outbreaks throughout the 20th century.
‘Polio is more explosive and more widespread,’ Dr Britton said.
‘I don’t want to suggest this is as big a problem, but we certainly need to monitor [NPEV strains], as they have the potential to become a big problem.’
While the viruses have been known to science for decades, the NPEV strains now causing concern are constantly evolving.
‘One thing about these enteroviruses is they’re very error-prone in how they replicate, with a real ability to recombine parts of their genetic makeup with other viruses,’ Dr Britton said. ‘That’s one of the real concerns – they’re much more like the flu virus, which is constantly changing and different.’
This mutability means that while the poliovirus vaccine has been remarkably successful, producing a vaccine for NPEV strains is much harder, according to Dr Britton.
China has been leading the push to a vaccine for the A71 strain, which has been responsible for more than 120,000 severe cases and more than 3300 deaths between 2008 and 2015. 
‘China has had the biggest problem with this virus. But no one knows how stable these vaccines are over time. For the D68, there is no vaccine,’ Dr Britton said.

Afghanistan is one of the only places in the world in which wild polio is still found. (Image: AAP)

Polio re-emerges in a new guise
The new concerns come even as poliovirus is on the ropes. The dreaded disease it could cause, poliomyelitis – which caused permanent paralysis in less than 1% of infections – led to one of the world’s most successful vaccination programs.
Two out of three wild poliovirus strains have been eradicated in the last five years, and all of Africa is now polio-free.
With wild polio now found only in Afghanistan and Pakistan, the world was anticipating the imminent eradication of the dangerous virus, in what would have been only the second virus – after smallpox – to ever be wiped out.
But as the current coronavirus pandemic shows, viruses pose a constant threat.
While poliovirus was brought down to its lowest ever levels in 2019, a recent resurgence of vaccine-derived poliovirus challenges the long hoped-for victory. There have been more than 460 cases of this form of polio worldwide this year – more than four times the number in 2019.
Polio experts say that, for every known case, there are about 2000 infections in the population, according to Nature.
The issue stems from the older poliovirus vaccines used across much of the world, which rely on weakened virus forms. These can, in rare circumstances, lead to a reversion to virulence.
‘It’s a catch-22 – the older polio vaccines are incredibly effective in controlling wild polio, but a very small proportion revert and can cause disease, especially in populations where vaccination rates are low,’ Dr Britton said.
‘In our region, Papua New Guinea and the Philippines have seen significant outbreaks of vaccine-derived poliovirus.’
While Australia uses inactivated polio vaccine, which cannot revert, people could be at risk if vaccination levels drop. 
‘Having high rates of this vaccine at a population level is still incredibly important to protect us from importation of poliovirus,’ Dr Britton said. ‘We’ve got 95% vaccination rates amongst children, the highest rate it’s ever been. We can’t lose focus on this incredibly important virus.
‘If the community at large understands how important these diseases are at a global level and in Australia, we can see that vaccination rate continue to rise.
‘I’m very aware GPs are at the front line of vaccinations and maintaining confidence in the community.’

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