Blinded by bodycount

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David Arthur John Tyrell, British virologist, and the first to culture coronavirus in vitro. Portrait by Oliver Hoeller

The coronavirus pandemic illustrates the fallacy of obsessing over mortality rates.

With diseases – whether infectious or non-infectious – we tend to obsess over bodycount. How many people are dying from the condition? What is the societal impact in terms of lives lost? How can we reduce the mortality rate?

Consequently, diseases that kill a lot of people – cancer, AIDS, malaria, TB, cardiovascular disease, diabetes – have tended to get the greatest attention, in terms of both publicity and research funding. Scientists who work on diseases that don’t kill a lot of people have usually had a harder time getting grants or visibility for their work, because it just doesn’t seem as important.

The coronavirus pandemic is showing how misleading such a fixation can be. A disease doesn’t have to kill millions of people – in fact, as the pandemic is showing, it doesn’t even have to kill hundreds of thousands of people (yet) – in order to have an effect on billions of people. A number of public figures, some in positions of considerable political power, have pooh-poohed the impact of the virus precisely because the mortality rate seems to be around the 1% mark. But the damage is being done not just by the mortality rate, but by the hospitalisation rate and the demand for intensive care – it’s the overloaded healthcare system.

It’s also revealed how a disease with a relatively low mortality rate – at least, compared to things like rabies, Ebola, and anthrax – can have an outsize economic effect. The behavioural countermeasures required to bring down the infection rate and buy time for the healthcare systems to absorb the impact of the contagion are resulting in global economic paralysis. Those countermeasures are 100% necessary, but are already resulting in widespread unemployment, bankruptcy, and a demand for bailouts. 

These insights are nothing new for researchers working on less prominent human afflictions such as the Neglected Tropical Diseases (NTDs). The NTDs are a group of twenty infections that disproportionately affect the global poor, and are highly prevalent in developing countries. The causative agents range from parasites such as trypanosomes, Leishmania, and schistosomes, to other organisms such as helminths, bacteria, and viruses.

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Source: Centers for Disease Control and Prevention

The NTDs get neglected not just because the majority of the people affected are too poor to pay for treatment, but also because many of the conditions are primarily debilitating rather than lethal. But the low bodycount doesn’t mean that they’re not having an impact.

The concept of disability-adjusted life years (DALYs) is an analytical tool intended to provide some kind of quantitative measure of this nonlethal impact. DALYs are calculated by summing not just the years of life lost through premature death, but also the years spent living with disease or disability. Consequently, DALYs encapsulate the often devastating effect of chronic infections that ruin people’s lives without necessarily robbing them of life itself. DALYs have been falling globally in recent years, but are still disproportionately associated with the lowest-earning social demographics.

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It’s intuitive too that sick and debilitated people are less economically productive. This is another insidious and easily overlooked aspect of diseases with low bodycounts. Affected people are either less productive or unable to work at all, meaning that the economic impact of infections can far outweigh their mortality rates.

Similarly, the anthropocentric perspective on disease means that the diseases of animals are easily disregarded in favour of things that affect people. But animal diseases can be a bigger problem economically than their human counterparts: sleeping sickness is on its way out as a human disease, but the animal affliction is still responsible for around 2.5 billion US dollars in lost agricultural productivity every single year in sub-Saharan Africa.  

And often, all it takes for one of these supposedly unimportant diseases to come roaring back is a relaxation in control measures. Sleeping sickness cases surged to some of their highest levels ever in the political instability that followed a lot of independence movements in Africa, and leishmaniasis is similarly seeing a dramatic increase in incidence in Syria and neighbouring areas – right now – as a result of conflict.

There will be many lessons to learn from the coronavirus pandemic, but one of them, surely, is that bodycount isn’t everything when it comes to assigning importance.

 

Disclosure: TIR writer Brooke Morriswood works on Trypanosoma brucei, the causative agent of human and animal African trypanosomiasis (sleeping sickness and nagana, respectively).

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