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Image by Arek Socha from Pixabay

How to Eradicate a Disease

We eradicated smallpox in 1980. What’s next?

In 1980 small pox was declared officially eradicated worldwide. In 2015, strain 2 of the polio virus was eliminated and this past October, strain 3 of the polio virus was also declared eradicated by the World Health Organization. That leaves only strain 1 of the polio virus left to deal with to completely eradicate polio in our modern world.

It was 1949. “I was playing with other children at a lawn party and developed such a terrible headache we had to go home. When I woke up the next morning, my legs were so weak I couldn’t stand on them and I could barely lift my arms. It took all day for the doctor to visit the house and examine me, and that night I was taken to the Englewood Hospital in Bridgeport and put in an iron lung.”For the rest of Judith Beatty's tragic and compelling story of her survival and life with polio, see this post.

Thankfully, in most of today’s countries, this no longer happens and even when polio is contracted, we certainly don’t put patients in an iron lung anymore!

How did we accomplish these feats of eradication and what do we need to do to eradicate many other infectious diseases? It turns out that there are 5 conditions that need to be satisfied in order to eradicate a disease:

  1. You need to be able to halt its transmission.
  2. The disease symptoms need to be unique and not able to be confused with some other disease.
  3. The disease must be able to be tracked effectively. It cannot infect someone who then becomes a carrier and shows no symptoms.
  4. We need to have a highly effective vaccine that completely clears the disease, even in people who have already contracted it.
  5. We need to be afraid of the disease. Fear is the most effective force to generate the political will and support necessary to make an effective and cooperative global effort that can successfully eliminate the disease.
Interesting note: There is a bit of confusion around the terms eradication and elimination.  Eradication is "the reduction of an infectious disease's prevalence in the global host population to zero."  Elimination is "either the reduction of an infectious disease's prevalence in a regional population to zero, or the reduction of the global prevalence to a negligible amount."

The eradication of smallpox is the classic example of the successful application of these 5 conditions.

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Photo from National Museum of Health and Medicine on flickr of a man with a smallpox rash.

Firstly, it only affects people. It doesn’t infect animals so once we eliminated it in people we were finished.

It satisfies conditions 2 and 3 because the rash that a smallpox infection causes is unique and won’t be confused with other diseases. And anyone who is infected develops the rash so there are no asymptomatic carriers.

Fourth, the smallpox vaccine is completely effective. You can even administer it to someone who was infected almost a week earlier and it will stop the disease dead in its tracks.

Lastly, people were very afraid of it. Even if you happened to survive the infection, you would be scarred for life. This created the kind of political pressure needed to make governments work together to make sure their citizens didn’t get smallpox anymore.

So where are we with the eradication of other infectious diseases? Let’s look a bit more at polio.

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Photo of children with polio from the RIBI flickr site

About 95% of people infected with polio are asymptomatic or display initial symptoms that are often quite generic — fever and headache are fairly common.

This means tracking the disease involves more complex surveillance methods. In this case, environmental samples are collected and tested and vaccines are administered until no more environmental samples or people in an area show positive test results for the polio virus. It’s slow and tedious but it can be effective and is how strains 2 and 3 were eliminated and how we hope to finally eliminate strain 1 to finish the task. Of particular interest is the fact that all the polio strain 1 still active in the wild is contained within Afghanistan and Pakistan. Eradication is targeted for sometime around 2023.

So what other diseases are likely to be eliminated in the foreseeable future? Wikipedia lists the 13 most likely candidates including Guinea Worm, Rubella, Measles, Malaria, and Rabies.

There are major efforts to eliminate all of these and more and several of them have already been mostly eradicated, with just small pockets left to deal with.

Here’s a current list of 9 diseases eliminated from the United States and the dates that the last endemic case was observed.

Given that there are over a thousand pathogens that still infect people, we obviously have a long way to go to eliminate disease on this planet.

But that doesn’t mean we shouldn’t congratulate ourselves on what we have accomplished this far. We have concentrated efforts on the most prevalent diseases that killed or permanently maimed millions of people worldwide every year and had great success.

With the advent of exciting new ways of using DNA sequencing and other new methods to identify and survey pathogens, we can hope for even greater and faster progress on these fronts.

As is so often the case, while the technology and opportunities exist for eradication, the public and political will and commitment do not.

Sad but true.

Until next time,


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