On the Horizon: an introduction

Earth from spaceOver the next few weeks and months, we’ll be publishing a collection of articles about emerging diseases in our On the Horizon series. In this first post, we spoke to David Heymann, Professor of Infectious Disease Epidemiology at the London School of Hygiene and Tropical Medicine, about the risks and reasons that these diseases emerge.

In December 2015, the World Health Organization (WHO) held a workshop in Geneva attended by microbiologists, public health experts, medics and mathematicians, among others. The aim of this meeting was to come up with a list – one that prioritised the emerging diseases that were most likely to cause large-scale outbreaks in the future. Of course, predicting which diseases may become problematic is difficult – just how serious the current Zika outbreak would become was unclear when this meeting was taking place.

This current list contains eight diseases, some you’ve heard of – like Ebola – and others that you may not have – Nipah virus, for example. Over the next few weeks, we’ll be publishing a series of articles about some of these emerging diseases, which can affect humans, animals or plants.

Prioritising these diseases is part of the WHO’s R&D Blueprint, which aims to speed up the development of treatments to prepare the world for future outbreaks, many of which have limited treatment options and disproportionally affect those in low- and middle-income countries. In addition to illness or death, these diseases carry a heavy economic burden, both for individuals and countries as a whole. For example, the World Bank estimates that the recent Ebola outbreak resulted in $2.8 billion worth of economic losses to Guinea, Liberia and Sierra Leone.

Risk

Whether you’re thinking about a bacterium infecting olive trees in Italy, or a virus passed from bats to humans in Bangladesh, emerging diseases have one thing in common: they’re complicated. For an outbreak to unfold, a series of seemingly disparate events need to occur in tandem. These could include increasing temperatures enlarging the habitat of biting insects, deforestation leading humans to come into closer contact with animals, or even the global trade of ornamental coffee plants.

This year, the European Centre for Disease Prevention and Control (ECDC) showed that the top five drivers for infectious disease events in Europe from 2008–2013 were travel and tourism, food and water quality, natural environment, global trade, and climate. The work also suggested that a combination of two or more drivers were responsible for a disease event.

If multiple drivers provide the foundations for an outbreak, then removing them will prevent one occurring. But how do you decide which one? As Professor Heymann explains: “It is necessary to review all the risk factors that are related to an outbreak, and figure out which ones can be mitigated, which can be delayed, and which can be prevented from occurring. Only then can you begin to deal with an emerging infection.”

Some of these risk factors appear easier to control than others, though none are without their problems. Take for example Rift Valley fever (RVF), a mosquito-borne viral disease that is endemic in ruminant animals in much of East Africa and can be lethal to livestock and occasionally spreads to humans.

One of the drivers for the emergence of infection in humans is climate change, with altered rainy seasons providing mosquitos with increased opportunity to breed and transmit the infection from animal to animal, and from animals to humans. Could tackling climate change be a fruitful way to reduce the risk of RVF? Probably not, given that humanity’s track record on tackling this issue could be described as patchy at best.

What about vaccination of ruminant animals to prevent their infection? Three vaccines are approved to protect animals against RVF, so why not introduce a mass vaccination programme? Sadly, vaccinations have their own problems – one can cause abortion in ruminants, which may prevent farmers from wanting to inoculate their animals, while another requires frequent booster shots, which can be difficult to administer in areas where farmers may be nomadic. Also, these vaccines are at times in short supply because of a variable market.

Another option to reduce the risk of RVF transmission is vector control, but this would be difficult to undertake on sufficient scale; likewise, preventing animal movement or trade would be difficult to enforce and would cause significant economic hardships.

And these are just a few examples from a single disease, the prevention of which will require a massively coordinated effort involving everyone, from heads of state to subsistence farmers. To solve this problem, everyone has to be on the same side, at the same time.

Funding

Regardless of whether you’re attempting to mitigate, prevent or stop risk factors, significant funds are required.

Recently, the World Bank announced the ‘Pandemic Emergency Financing Facility’ (PEF), an insurance system that will quickly make funds available to low-income countries and international agencies during the early stages of an emerging disease outbreak.

The rationale here is that an early injection of cash will prevent an outbreak event growing into something unmanageable. They cite the Ebola outbreak as an example, suggesting that if the PEF had existed in early 2014, $100 million could have been quickly spent to bring the outbreak under control. Instead, they estimate that the international community spent a staggering $7 billion to tackle the outbreak in West Africa.

But if insurance can be considered a reactive way to respond to an outbreak, can existing funds be used more effectively to prevent outbreaks from happening in the first place?

As David explains: “First, countries must understand that [these diseases] are something they need to prioritise. An international fund can pour vast sums of money into a country, but if a government is not engaged in the need to prevent outbreaks by tackling the risk factors at the source, it won’t be spent properly. It’s not a matter of money alone, it’s a matter of government engagement as well.

“There’s also the matter of governments deciding what their priorities are. They might not, for example, identify RVF – which has the potential to cause small but lethal outbreaks among humans – as a priority, because the priority for them may be AIDS or malaria, both of which are endemic and kill many children and adults each year. It’s a process, not just ‘here’s the money, do the job’ – it just doesn’t work like that.”

Challenges

While the modern world, with its increased globalisation, urbanisation and altered climate provides a new set of problems for disease prevention, it also offers a new set of potential solutions. Services like ProMed are allowing researchers and public health workers to rapidly alert others across the world to diseases events as they occur. Modern genomics and data sharing platforms allow researchers to share data and collaborate faster than ever before.

However, the ability to share this information so quickly brings its own challenges, particularly surrounding the traditional peer-review publication model and the delay between experiment and publication. In response to the Zika outbreak, a group of influential science funders and publishers agreed to make all content related to the virus free to access and rapidly available, while Chatham House are working with the Gates Foundation to set up a framework for best practice for sharing public health data in the future.

The future

We seem to hear about new outbreaks with increasing regularity – but is this a reflection of what’s really happening, or simply due to better surveillance and increased media coverage?

Either way, the need for collaboration and transparency is paramount if we are to prevent localised outbreaks becoming more serious. Previous examples – such as the outbreak of SARS in 2003 – have shown that failure of governments or public health officials to alert the global community can make a bad situation much worse and lead to preventable fatalities.

However, David suggests that prevention is better than cure:

“What we, as a global community must do, is to think less about rapid detection and response – which are necessary as a safety net – and more about prevention at the source. We have to change the paradigm from rapid detection and response to understanding the basic reasons that diseases emerge, and develop the public health capacity to prevent them from occurring, or if they do occur, to rapidly detect and respond.”

Benjamin Thompson

Our next On the Horizon article will look at efforts to control rat populations in Sierra Leone as a means of controlling Lassa fever.

Image credit: NASA Goddard Space Flight Center on Flickr under CC BY 2.0
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