The Eradication Game

In the game of viral infections versus humans, viruses have been winning for a few thousand years. However with massive advances in research and global health policy, we are starting to take the upper hand.

Written by: Helena Winstone

Art by: Yang Xin


An important 40th birthday

2017 marks 40 years since the last documented natural case of smallpox and 2020 will mark 40 years since its official eradication by the WHO. Following the successful elimination of a disease which caused between 300–500 million deaths in the 20th century alone, the WHO has chosen polio as the next virus to eradicate from the planet: and with polio now only endemic in two countries, its elimination is in sight. So with our understanding of viral infections exploding like herpesvirus DNA out of its capsid (which has the force of popping a champagne cork if you want a fun fact for down the pub), will we see a burst of eradicated viruses in the next 40 years? And if so, where should the line be drawn?

 

A case of beginner’s luck?

So, after our initial success of abolishing one of the world’s most lethal viruses half a century ago, why is polio proving more difficult to eliminate? Until its eradication, smallpox was one of the most feared diseases in the world, killing 1 out of every 4 people infected and leaving survivors with lifelong scars. However, smallpox’s blatant visual severity was one of the key factors to its eradication. The obvious symptoms of smallpox infection meant quarantine of patients was fast and effective in preventing spread of the disease. Additionally, one vaccine against smallpox conferred long-lasting immunity and as the virus only infected humans,  there were no other animal reservoirs it could emerge from. Polio, on the other hand, incurs significantly more difficulties. 90% of people infected with polio are asymptomatic, meaning they can transmit the disease to many other people before an outbreak is identified. This also poses issues for maintaining polio’s eradication status after the last documented cases,  as the virus could in fact still be present asymptomatically and re-emerge. Furthermore, unlike smallpox, one vaccine is not enough to generate lifelong immunity to polio, so multiple vaccinations are needed. This is not always possible in countries and areas that are most vulnerable to polio due to accessibility problems caused by migrating and extremely rural populations.

 

Are other eradications in sight?

A world free of polio is in sight, as only two countries are still endemic for polio and two of the three types of polio have not been documented as a natural case for over 10 years. According to the WHO, once polio is eradicated, measles will be the next focus. Measles is an incredibly infectious disease, which resulted in nearly 90,000 deaths worldwide in 2016. It is estimated at least 93% of a population would need to be vaccinated in order to prevent measles transmission (key to eradication), but last year only an 85% vaccination coverage was achieved worldwide. However, vaccinations against measles are increasing, and it is entirely possible that in 40 years time measles may also be eliminated.

 

Where do you draw the line?

Several of the viruses responsible for high disease prevalence and death rates, such as hepatitis C, the leading cause of liver cancer, are expensive to treat (meaning this isn’t always possible in the places that need it most), and are difficult to design vaccines for due to their structure and rapidly changing genetics. However, assuming that we will reach a point where we can eradicate these illnesses in the future, where do we draw the line of which infections should be eliminated? For example, how beneficial would it actually be to eradicate the common cold, herpesvirus 1 (cause of cold sores and asymptomatically carried in over two-thirds of the population) and chickenpox? Some immunologists would argue that this would do more harm than good. The challenge that our immune systems regularly receive from these less severe infections are crucial in order to keep them primed for dealing with more dangerous pathogens. Additionally, keeping the immune system busy with minor challenges is also a key factor in preventing it from going into overdrive, leading to autoimmune disease. If we removed these viruses, it’s possible that the allergy and autoimmune epidemic we are currently facing would rise even further. There is also the question of whether there would be any other unforeseen consequences of removing  agents that we have evolved with over thousands of years. Approximately 8% of our genome is estimated to be from viruses that have integrated and then become defective, and we have inherited some incredibly useful genes this way. Syncytin, for example, the gene responsible for placenta formation in pregnancy, is virus derived.

Although eliminating viruses that cause severe diseases is key for relieving significant health burdens, removing the smaller fry might do more harm than good – office workers, the dream of getting through the winter without catching Susan’s cold might just be a pipe dream after all.

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