With the appearance of a polio outbreak recently, I wanted to clear up some misinformation (from anti-vaxxers) regarding non-polio enterovirus linked to an outbreak of children’s respiratory disease. There is no relationship between the polio outbreak and the outbreak of non-polio enterovirus, and there is certainly no relationship between either and vaccines.
For this article, I’ll focus on the non-polio enterovirus. There is a lot to this situation, so stay tuned for some science.
What is a non-polio enterovirus?
Enteroviruses are a genus of several RNA viruses that are associated with numerous diseases that afflict humans and other mammals. As of today, researchers have identified 84 different serotypes of human enteroviruses, although there is some variability in antigens within each of the different serotypes.
Early in the research on these viruses, they were given separate names, such as polioviruses, Coxsackie A viruses, Coxsackie B viruses, and echoviruses. Today, the viruses, as they are identified, are given names in a system of consecutive numbers. Enterovirus 68 (known as EV68, EV-D68, or HEV68) is the 68th on the list of these viruses.
Although many people claim that enteroviruses are only transmitted from the stool of an infected person (hence the “entero” portion of the name of the virus), they also can be found in respiratory secretions.
Probably, the most famous enterovirus is the poliovirus which is responsible for poliomyelitis. Poliovirus is an enterovirus, but not all enteroviruses cause polio.
There are 81 non-polio and 3 polio enteroviruses that can cause disease in humans. Of the 81 non-polio types, there are 22 Coxsackie A viruses, 6 Coxsackie B viruses, 28 echoviruses, and 25 other enteroviruses. Several of these viruses, such as poliovirus, are transmitted through the oral-fecal route, but others can be transmitted through oral-oral routes like simple sneezing.
According to the CDC, there have been many non-polio enterovirus outbreaks across the world recently:
- Coxsackievirus A16 is the most common cause of hand, foot, and mouth disease (HFMD) in the United States.
- Coxsackievirus A6 was the most commonly reported type of enterovirus in this country from 2009 to 2013, mostly due to a large outbreak in 2012 of severe hand, foot, and mouth disease. Some of the infected people developed symptoms that were more severe than usual.
- Coxsackievirus A24 and enterovirus 70 have been associated with outbreaks of conjunctivitis.
- Echoviruses 13, 18, and 30 have caused outbreaks of viral meningitis in the United States.
- Enterovirus 71 has caused large outbreaks of HFMD worldwide, especially in children in Asia. Some infections from this virus have been associated with severe neurologic diseases, such as brainstem encephalitis.
- Enterovirus D68 outbreaks have been documented in 2014, 2016, and 2018, causing respiratory illness in the United States
So, enteroviruses are quite common and have been associated with numerous outbreaks across the world. However, for this article, we are going to focus on enterovirus D68 or EV-D68.
Enterovirus D68
I first became aware of EV-D68 when I read a 2014 report from the CDC which described results from testing of 23 children in California who had presented with polio-like syndrome or acute flaccid myelitis. The syndrome includes muscle weakness or paralysis along with an infection of the grey matter of the spinal cord. In general, these are similar to the symptoms of paralytic polio, though many other viruses can present with the same symptoms (see note 1).
EV-D68 almost always causes respiratory illnesses, which can vary from mild to severe. However, the symptoms can range from almost asymptomatic to flu-like to polio-like. Generally, the initial symptoms are like the common cold, which includes a runny nose, sore throat, cough, and fever. As the infection progresses, more serious symptoms may arise up to and including flaccid paralysis.
The majority of people who are exposed to EV-D68 may not realize that they’ve contracted the disease. In healthy adults, the disease is mostly asymptomatic, and they may not even know that they had contracted the virus. However, EV-D68 is disproportionately debilitating to very young children. This article focuses on the effects on children.
Current situation
Physicians have reported an increase in hospitalizations of children across the country presenting with severe respiratory illnesses in August 2022. US healthcare providers reported an increase in children hospitalized for severe respiratory illnesses who also tested positive for rhinovirus (RV) or enterovirus (EV). Upon further testing, more of those cases tested positive for enterovirus D68, which is a non-polio enterovirus linked to uncommon neurologic complications.
According to a CDC Health Alert Network advisory announced on 9 September 2022, these illnesses may be linked to the non-polio enterovirus, EV-D68.
Furthermore, this enterovirus may also be linked to a rare neurologic condition, non-polio acute flaccid myelitis, or AFM. The condition affects an area of the spinal cord called gray matter. This can cause the muscles and reflexes in the body to become weak. This is similar to polio, but it is not caused by the poliovirus.
As of Aug. 30, the CDC has not received any reports of AFM cases. “However, increases in EV-D68 respiratory illnesses have typically preceded cases of AFM, indicating that increased vigilance for AFM in the coming weeks will be essential,” the agency stated.
Relationship to vaccines
There is none, but I guess I need to support my claim with scientific evidence.
In a recent study published in the respected journal Eurosurveillance, a journal that specifically focuses on infectious diseases and epidemiology, Australian researchers focused on this 2014 outbreak of acute flaccid myelitis. EV68 is a rare virus, and initially, it was never considered to cause polio-like syndrome.
The researchers drew on 20 published studies that had focused on the polio-like syndrome outbreak and EV68. Using the Bradford Hill criteria, the researchers quantitatively analyzed each of the points that establish causality, the authors concluded that:
In summary, the application of the Bradford Hill criteria suggests that EV-D68 causes AFM. AFM has not previously been associated with EV-D68, and a mouse model shows that the original Fermon strain does not cause AFM, whereas the 2014 outbreak strain does. It appears that the incidence of this infection and the clade-specific epidemiology have changed. Phylogeographic epidemiology will further our understanding of the temporal and spatial spread of increasingly neurovirulent clades and improve risk analysis. Further investigation into this relationship is important because of the severity of AFM, ongoing outbreaks of AFM and because there is currently no treatment for AFM related to EV-D68, and no vaccine to prevent infection.
That’s a lot of solid evidence that EV68 probably was the infectious agent that caused the outbreak of polio-like syndrome, acute flaccid myelitis. And we have pretty solid evidence that it was not polio or vaccine-derived poliovirus (VDPV), a very rare virus caused by the mutation or recombination of the attenuated viruses used in the oral polio vaccine (OPV).
Nevertheless, the anti-vaccine crowd tries to claim that the polio vaccine created EV-D68, which led to the acute flaccid myelitis outbreak. As I wrote above, EV-D68 is related to polioviruses – they are in the same genus, Enterovirus. But, saying that EV68 is the same as poliovirus is scientifically incorrect, by a long way.
It is nearly impossible to determine when the common ancestor of the poliovirus and EV68 diverged during the evolution of enteroviruses, but they are so different that EV-D68 RNA cannot recombine with poliovirus RNA. They have completely different protein coats which means when EV-D68 meets up with poliovirus, they’re as different as a dog and cat – they’re both furry and all, but they would rather not have much to do with each other.
VDPV is extremely rare, and generally, it is only a concern in populations that have low levels of vaccination against polio. In populations with high levels of polio vaccination, people would be immune to the VDPV, since its antigens are the same as wild-type poliovirus.
It is important to note that the AFM outbreak occurred mostly in countries, like the USA and Canada, where the typical vaccine used is the injectable polio vaccine (IPV) which uses inactivated poliovirus and cannot replicate or mutate.
In other words, if you’re trying to blame the polio-like syndrome outbreak on the polio vaccine, at least in most of the world which uses IPV, those claims are implausible if not impossible.
Notes
- There appear to be several interchangeable medical terms for the same disease. For this article, I will stick with either polio-like syndrome (some people call it a polio-like illness) or acute flaccid myelitis, even though they aren’t completely interchangeable. In addition, acute flaccid paralysis with anterior myelitis has been used to describe polio-like syndrome, although acute flaccid myelitis is now the most common term.
Citations
- Dyda A, Stelzer-Braid S, Adam D, Chughtai AA, MacIntyre CR. The association between acute flaccid myelitis (AFM) and Enterovirus D68 (EV-D68) – what is the evidence for causation? Euro Surveill. 2018;23(3):pii=17-00310. doi: 10.2807/1560-7917.ES.2018.23.3.17-00310.
