Polio, vaccination and disease eradication

Use our cuddly poliovirus to learn how we can prevent and eradicate diseases!
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Cuddly poliovirus

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There are a few key concepts you can talk about with polio, depending on how keen the children are and their level of understanding:
• The virology of poliovirus; how it replicates etc.
• How poliovirus causes disease
• Vaccination
• Disease eradication

The Virology
This is quite hard to explain without getting bogged down in detail. For most children, I’d restrict it to explaining that polio is a virus, so it needs to hijack our cells to make more of itself.
Polio is a virus which can cause a disease called poliomyelitis. Viruses are incredibly small particles (virions) containing the genetic instructions needed to make more virions. To infect a cell, the virus sticks to the cell surface then injects its RNA (the genetic instructions) into the cell (if we’re being precise, the whole virion is internalised by receptor-mediated endocytosis before the genome enters the cytoplasm, but we can probably skip this).
The host cell is then ‘tricked’ into producing thousands of new virions; the RNA has the instructions to make the viral proteins and also acts as a template to produce more genomes. Eventually, the cell bursts, releasing up to 10,000 new virions into its environment, ready to infect more cells.

How polio causes disease
Polio spreads by the faeco-oral route; ie poo contaminating drinking water. That’s why it’s often seen in areas with poor sanitation (eg. poor sewage disposal, no water treatment). It’s also the reason that young children are more likely to get infected, since they tend to have lower standards of hygiene!
The vast majority of people infected get a fairly harmless infection in the gut or get vague ‘flu-like’ symptoms.
Polio becomes a problem if it infects cells called motor neurones in our spinal cord. We need these cells to control our muscles, so if lots of them are killed then the muscles become paralysed (becuase information can't get from the brain to muscles to tel them what to do). The resulting disease is paralytic poliomyelitis, which is what most people think of when you mention polio. Interestingly, infecting the cells in the central nervous system does not help the virus transmit to other hosts (it is 'accidental' infection - the virus would benefit more from infecting cells which can allow replication and transmission to new cells, so infection of these motor neurons is a waste of its resources)

What effects can paralysis have? It depends on where is affected. Obviously, if the legs are affected the patient won’t be able to walk. Even worse is bulbar poliomyelitis, where the muscles we use to breath can become paralysed.
There isn’t a cure for polio. All we can do is support the patient to keep them alive. If their breathing muscles become paralysed then they need mechanical ventilation, meaning that a machine is used to do the work for them. Famously, in the 1950s this took the form of negative pressure ventilation, aka the iron lung

Polio affected thousands of people in the Western world in the 1950s. But ask the children how many people they’ve met who’ve had polio. The answer should (hopefully!) be none. Why? Because there’s a vaccine to prevent it!
Normally our bodies fight infections using our immune systems. Our immune system ‘learns’ how to fight an infection when it’s exposed to the pathogen, so it fights it more effectively the second time around. That’s why we normally only get chickenpox once, even though it’s a really infectious disease. Vaccines are a way to teach our immune system to fight a disease.
Different vaccines work in different ways; some use a dead pathogen or part of a pathogen, while others use a live one that’s been deliberately weakened so that it’s no longer able to cause disease, but still similar enough to the dangerous one that our immune system learns to fight that one too.
In the case of polio, there are actually vaccines that work both ways; the live vaccine is more ‘realistic’ so it produces more effective immunity, but there’s a risk that the ‘safe’ strain can mutate back into a ‘dangerous’ one. In the UK we use the dead vaccine, since you’re highly unlikely to be exposed to polio anyway, but in areas where polio is still common we use the live one, since the benefit outweighs the risk.

Disease eradication
The polio vaccine is important because it might be possible one day to use it to eradicate polio completely. In fact, we’re tantalisingly close to doing so!
Have they heard of any other diseases that have been completely eradicated? There’s only one human disease: smallpox. For the vets, there’s also rinderpest - infected cows, buffalo, deer, giraffes etc)
Polio has certain special features which are needed for a disease to be eradicated:
• It doesn’t change so much over time that the vaccine stops working. Contrast with flu, where we need a new vaccine very year, and even that isn’t guaranteed to work!
• It doesn’t infect animals. Animal viruses which also infect humans are basically impossible to eradicate, since it just needs one person to be infected by an animal and we’re back to square one. Sadly, this applies in the case of Ebola.
We’ve come incredibly close to eradicating polio in recent years, and it’s now largely confined to Nigeria, tribal regions of Pakistan and Afghanistan. However, these areas are all highly politically unstable and health workers have been targeted by violence, so it remains to be seen whether the final push will be successful.

Risk Assessment
Date risk assesment last checked: 
Sun, 20/01/2019
Risk assesment checked by: 
Matt Worssam
Date risk assesment double checked: 
Mon, 21/01/2019
Risk assesment double-checked by: 
Risk Assessment: 
Hazard Risk Likelihood Severity Overall Mitigation Likelihood Severity Overall
Cuddly poliovirus Trip hazard if dropped 2 2 4 Keep all props in contained area. If toy is dropped, pick up as soon as is safe.
Put away the toy before leaving the experiment unattended.
In case of injury, call first aider.
2 1 2