The Plague of Justinian began in 541 AD and ended the following year. During that time, it claimed 50 million lives and killed up to 40% of people living in the Byzantine capital of Constantinople. Meanwhile, smallpox may have killed as many as half a billion people in just the 20th century and according to the United States Library of Medicine, tuberculosis was causing 900 deaths per 100,000 inhabitants each year in the 18th century

Clearly, the past was rife with epidemics that make COVID look mild. Since then, medical advances have helped protect us from the diseases that claimed millions of our ancestors. The plague and tuberculosis are both treatable. Smallpox has even been eradicated. However, this doesn’t mean that the shocking death toll caused by infectious diseases in the past is behind us. The COVID19 pandemic has killed millions of people around the world, reminding us that viruses can still cause mass death and bring whole countries to a standstill. Even more concerningly, COVID is unlikely to be an isolated event. If we aren’t careful, we could find ourselves in a future as deadly and disease-ridden as our past.

Firstly, human encroachment on animal habitats dramatically increases the risk of future pandemics. Estimates suggest that 60% of the diseases (including COVID19, ebola, and HIV) that affect us are zoonoses, or pathogens, that originated in other animals. Closer and more frequent contact between species increases the chances of this process happening. Habitat destruction creates the perfect conditions for zoonoses to emerge, not only because it sometimes involves humans entering previously wild areas, but also because it can displace animals into settled areas nearby. An example of this dynamic can be illustrated by the first Nipah outbreak in 1998/99. Large areas of forest were cleared using slash and burn techniques in Indonesia, leading to smog so thick that it hindered photosynthesis. This contributed to trees not fruiting, driving bats to Malaysian farms in search of food. As a result, the Nipah virus crossed from bats to pigs and then from pigs to farmers. Although it rarely causes symptoms in bats, Nipah virus can lead to severe encephalitis in humans and has a mortality rate between 40% and 75%, leading to hundreds of deaths in the 1999 outbreak.

It could be argued that even the emergence of new zoonotic diseases wouldn’t be enough to plunge us into an age of pandemics. After all, medicine has advanced significantly since the Plague of Justinian and other devastating health crises in Antiquity. We understand that microorganisms cause diseases. We have vaccines and antibiotics to combat viruses and bacteria. However, it’s important to remember that developing effective medical responses to new pathogens takes time. For example, vaccine development takes 5-10 years on average. Although medical advances can eventually curb a pandemic, this could easily take a decade or longer. In the case of Nipah virus, there still isn’t a vaccine or a cure even after more than twenty years. In the absence of modern medical treatments, we have to resort to ancient techniques like supportive care and isolation whenever we’re faced with a new disease.  

Furthermore, encountering new pathogens isn’t the only threat we face. Political opposition to vaccination around the world risks bringing back diseases we thought we’d defeated. For example, the Taliban banned vaccine drives that had been part of an attempt to eliminate polio in protest of US military operations. Nor is anti-vax sentiment limited to low-income, authoritarian countries. According to a 2011 poll, 18% of Americans were convinced that the MMR (measles, mumps, and rubella) vaccine causes autism. Even more concerningly, 16% of respondents said they knew somebody who had refused to vaccinate their child due to fears about vaccines. Unsurprisingly, measles outbreaks in the US have been linked to unvaccinated clusters. 

However, despite how common doubt about the safety of vaccines is in the US, the country has maintained a 92% vaccination rate. Given that the minimum threshold for achieving herd immunity for measles requires 92-94% of the population to be immunised, it can be concluded that the anti-vax movement has not had serious or widespread consequences. The situation is different when anti-vaxxers are not a vocal minority and are instead in power, such as the Taliban in Afghanistan. However, even in cases like that, there is still the potential to bring vaccination rates back up through negotiation, diplomacy, and (if helpful) external pressure. In 2021, the Taliban agreed to a WHO vaccination campaign and rekindled hopes that polio could be eradicated at last. 

Unfortunately, some diseases could be making a resurgence through other means. Several species of bacteria are slowly evolving a resistance to the antibiotics used to treat them. This trend can clearly be seen with tuberculosis. Multidrug-resistant tuberculosis (MDR-TB) cannot be treated with isoniazid or rifampicin. Instead, second-line treatments which can be thousands of times more expensive and can have severe side effects like hearing loss, kidney problems and psychosis must be used. The prognosis for patients with MDR-TB is often grim. Despite years of gruelling treatment, only 56% of them will be cured. The situation may only get worse as TB continues to evolve. Already present are strains of TB which are extensively drug resistant (known as XDR-TB). These not only don’t respond to isoniazid and rifampicin, but are also resistant to some forms of second-line treatment, further complicating treatment and lowering the patient’s chances. According to the WHO, treatment for XDR-TB is only successful in 34% of cases. In the worst-case scenario, we could find ourselves living in a world where antibiotics rarely work.

However, that eventuality is completely preventable. Resistance in bacteria is mostly due to misuse and overuse of antibiotics. For example, stopping treatment early can lead to the formation of resistant strains as the antibiotics may not have killed all the bacteria yet. Those that survived are likely to have higher resistance to the drug used than the others, as will their offspring. Over repeated mistakes with treatment and successive generations, the bacteria are increasingly able to survive treatment. As a result, it’s important to use antibiotics properly and only when necessary. Sadly, this is rarely the case in practice. 30% of antibiotics prescribed in 2015 in outpatient settings were unnecessary, while a survey of WHO countries found that 32% of people were not aware that they should finish the prescribed antibiotic regimen even if they were feeling better. Of course, these problems can be easily resolved through information campaigns and training for medical professionals. 

We are heading towards a future of mass disease. As we destroy animal habitats we will increasingly see devastating epidemics and witness pandemics claim millions of lives. We will also see more people die from resistant strains of the bacteria that have always plagued us. However, there is still time to reverse the course. By limiting habitat destruction, we can drastically reduce the dangers of zoonotic diseases spreading out of control and claiming even more lives in the future. Although there’s little we can do about the resistant strains of bacteria we currently have, we can reduce the chances of more emerging in the future by prescribing and using antibiotics responsibly. Medicine has progressed dramatically since antiquity. We mustn’t let our carelessness reduce the incredible gains we’ve made.

Featured image by: cromaconceptovisual / pixabay

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