Why does our health depend on biodiversity?

As climate change and biodiversity loss intensify, so will pandemics

Since 1970, the world’s population has doubled. The impacts on the earth’s climate and ecosystems, which humans share with other species as well as population-regulating pathogens, are undeniable. As we destroy habitats to make room for human population growth our contacts with wildlife – and their pathogens – also increase. Does this mean more pandemics in the future?  According to Professor Killeen, “the short answer is yes; we should expect more pandemics.” He is quick to add, however, that “this problem has been going on for quite some time.” By way of example, he points to the emergence of HIV. “Simian immunodeficiency virus (SIV), the primate version of HIV, has been regularly infecting individual humans in Central and Eastern Africa for hundreds of years. But it’s only really in the second half of the 20th century that it became established as a human disease, through human-to-human transmission,” resulting in a series of outbreaks. For Prof Killeen, the key takeaway from this and similar examples is that “once things start to happen, they are going to happen regularly. That’s going to be the case for a lot of new pathogens, like Covid-19.”

Crisis as a wake-up call and opportunity for global solidarity

For many people on the planet, Covid-19 is their first close encounter with a pandemic, although, as Prof. Killeen says, such pandemics are not new and “have been somebody else’s problem until now.” And though the global reach of this virus – which Prof. Killeen notes “has really reached out and touched all of us” – has not been seen in a century, several pathogenic outbreaks have occurred over the last decade, including SARS1, MERS, and Ebola. All became global pandemics after being contained regionally. A pandemic of this scale, he says, “challenges our humanity and the way we perceive what’s important.” It’s important to settle national issues now, “because we have a global challenge to undertake.” International solidarity is even more difficult when borders must be closed, but achieving the latter requires global cooperation. And that’s not all. “We need to preserve biodiversity in a manner that minimizes the risk of new pathogens emerging into humans. We need to adapt veterinary quarantine measures to human diseases. We need to control human pathogens at borders, and we need to be particularly careful of invasive species.” For many of us, this is a wake-up call to an issue that’s been “brewing for a long time.”

What we can learn from emerging countries

Working in Tanzania and other parts of Africa, Prof. Killeen learned “the value of simply just not giving up.” In nationwide malaria control programs and HIV programs across Africa, entire populations have mobilized to contain deadly disease outbreaks, including cholera. As Prof. Killeen recalls, the cholera outbreak involved “closing all restaurants and informal food outlets and bans on serving food outdoors.” He says the Nigerians “saved the world from Ebola back in 2014 when they traced over 500 people across Lagos, a huge metropolis and travel hub.” Is there a lesson? “All kind of things are possible. It’s easy to look at the empty half of the glass but we really need to focus on the full half and look at all the great successes in public health.” There are many, particularly in some of the poorest countries, where people are used to hardship and emergencies. “Let’s put it this way,” says Prof. Killeen. “This is not my first lockdown, but it’s by far the most comfortable one. There’s a lot to learn, particularly from low- and middle-income countries.”

How this pandemic differs from others and why a global lockdown was necessary

​Prof. Killeen has set aside his work on malaria to focus on coronavirus pathogen transmission modelling. He says many coronavirus challenges resemble those seen in the malaria field. For one thing, “an awful lot of people who have the disease either don’t know it or it’s mild enough that they shrug it off.” With epidemics like Ebola, where people get very sick, epidemiological surveillance is effective. But when most cases are mild or asymptomatic, “they tend not to be picked up and even if you put in place a very active surveillance system, these mild symptoms overlap with other very common pathogens.” Due to the variable, non-specific nature of this pathology, tracing only symptomatic cases means that “basically you have to test everyone with any symptom of anything.” Consequently, the usual battery of interventions – testing, treating, contact tracing – is not effective and, as with malaria, “the approaches we take must be preventative, presumptive, and preemptive. We have to stop the epidemic before it starts and deal with the clusters before they arise.” This is why a global lockdown was necessary: “If you can’t tell who’s infected, you need to ask everybody to protect themselves and the people around them, the same way we ask everybody to use a bed net to protect themselves and their neighbors against malaria.” Ultimately, this means adjusting to a new normal – not going shopping even though you feel fine, not rubbing your eyes, etc. – which poses a conceptual challenge but also saves lives.

Learn more about Gerard Killeen.