The past, present and future of disease

Sambhavi Sneha Kumar

23 November, 2021

Pathology is a field of concentrated research effort and subsequent progress as we strive to further our understanding of what causes disease. As we increase our knowledge of the basis of disease by learning from the past and studying the present, we further our capacity to reduce the global disease burden now and in the future, for example through public health initiatives. 

The ‘world’s biggest killer’ was revealed to be ischaemic heart disease by the World Health Organisation (WHO) in 2019, responsible for an estimated 9 million deaths in the year. Switching lanes to look at a rather different kind of disease, the COVID-19 pandemic recorded significantly fewer direct deaths compared to ischaemic heart disease in its most severe year, but it has still brought the world to its knees.  Arguably, what makes a disease ‘dangerous’ is not fully represented by a mortality rate. Other factors to consider may include our ability (or lack thereof) to provide treatment. For example, many degenerative and age-related pathologies such as Alzheimer’s disease (7th on WHO’s 2019 list) represent a greater threat in the face of the ageing populations of many countries, because our understanding of the cause is less concrete. Similarly, cancers can also be considered one of the most dangerous pathologies faced by humans. Despite the lower mortality rates compared to other diseases, there is such a vast quantity of research that may be yet to be done. 

One thing is evidently clear – the challenges posed to human health globally are extensive. Some can be linked to our increasing lifespans, others to lifestyle choices such as diet or smoking, and others – think pandemics – perhaps to increased travel capabilities. In fact, many common pathologies of the 21st century can be connected in some way to various technological advances that have arguably paved our way to our most significant developments as a species. But just how significantly have the diseases we face changed with time? 

 

“Many common pathologies of the 21st century can be connected in some way to various technological advances that have arguably paved our way to our most significant developments as a species”

 

In terms of pathogen exposure, the ‘microbial profile’ of our planet does, of course, change with time. Whilst we have only managed to completely eradicate two pathogen-caused diseases to date – smallpox and rinderpest – increased immunity to many diseases, acquired either naturally following infection or artificially after vaccination, means that many pathogens that may have historically ravaged populations are now a much less significant threat. 

Indeed, one of the most intriguing plot-holes that causes time travel in science fiction to come unstuck is the apparent universal immunity. In the ever-popular jump into the future, any heroic protagonist would find themselves overwhelmed with new pathogens for which they have no natural immunity, which would likely be fatal in the absence of any intervention. Equally, they would likely be carrying pathogens that could be deadly for the future society. Whilst this fictional idea is arguably rather removed from our everyday, more realistic concerns, it remains true that even for a single pathogen within the relatively short time of for example a year, in some cases sufficient antigenic change can be accumulated to render past immunity ineffective. This has implications for strategies to tackle these pathogens, as healthcare services attempt to prevent recurring disease outbreaks. Antigenic change of the influenza virus is a classic example: within a single lifetime, eligible individuals may receive multiple flu vaccinations – typically annually – to account for the continuous change in the virus’ surface antigens, occurring  randomly and perhaps subsequently conferring a survival advantage. Our ability to respond and react to new pathogens is continuing to improve (the rapid development of vaccinations for COVID-19 being a good example) but the battle to outrun them will likely remain difficult to win. 

Cardiovascular pathologies are a significant cause of death worldwide; their incidence has featured a recent increase over the last few generations. They accounted for multiple of the ten most common causes for death outlined by WHO in 2019. It is worth noting that our understanding of the epidemiology of cardiovascular disease over time is somewhat limited by our understanding of cardiovascular physiology. For example, whilst William Harvey’s famous description of the circulation is pinned to the year 1628, following work was slow. It is believed that the heart itself at a macroscopic organ level only became a specific object of study for disease in the nineteenth century. Many cardiovascular diseases can be viewed to an extent as a product of modern living, but our understanding of these pathologies did take time to develop, and indeed we have more yet to learn. 

However, there is no denying that some of the biggest challenges to good cardiovascular health – such as excessive tobacco usage – did see a significant rise in prevalence in the 20th century. This rise brought with it an increased number of deaths due to coronary heart disease, the so-called ‘epidemic of the 20th century’. However, after peaking in the mid-1960s, many countries were able to overturn this, largely through thorough and persistent public health initiatives. In Britain, the majority of the reduction in coronary heart disease mortality between 1981 and 2000 has been attributed to reductions in major risk factors (notably, smoking), though improved medical and surgical treatment strategies have also played a role. This is encouraging, simply because it demonstrates that once the mechanisms underlying certain pathologies and the associated risk factors are identified, steps can be taken at societal and individual levels to protect the health of both the former and the latter. 

Naturally, this leads us to consider pathologies for which the basis is not completely understood. Many of these diseases are relatively newly emerging as the products of increasing life expectancies and so initially prior data was limited, and identifying specific lifestyle factors or a pathogen may well be of limited utility. However, if the pathogenesis can be understood, treatment options can be proposed. For example, one of the hallmarks of Alzheimer’s Disease, is a severe loss of cholinergic neurones in the basal forebrain; treatment strategies acting on the cholinergic system to oppose this may show promise. 

Regardless of how advanced medical technology becomes and regardless of the extent to which good public health is advocated for, pathology will continue to challenge human health in some form. There is much that remains to be learnt about disease, and improved diagnosis and management will continue to play a role in our handling of it. 

 

Declare the past, diagnose the present, foretell the future- HIPPOCRATES

 

In the upcoming weeks, this blog for the Pathological Society Undergraduate Network will be speaking to a range of pathologists at the front of their fields. We will be exploring the latest research investigating the basis for some of the diseases mentioned in this article, and thinking about the future implications. Stay tuned!

 

Featured image: Tumisu, pixabay.com