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As $4 and other $4 ravage the world and the $4 looms, it's hard to assess which risks for humanity are really the scariest right now.
But one of the biggest threats out there is one of the oldest: infectious disease, which can emerge naturally or be human-made, as in a case of bioterrorism.
As Bill and Melinda Gates wrote in their recently $4, disease - both infectious and chronic - is the biggest public health threat the world faces in the next decade. And although Gates said on a press call that "you can be pretty hopeful there'll be big progress" on chronic disease, we are still unprepared to deal with the infectious variety.
Gates has repeatedly stated that he sees a pandemic as the greatest immediate threat to humanity on the planet.
"Whether it occurs by a quirk of nature or at the hand of a terrorist, epidemiologists say a fast-moving airborne pathogen could kill more than 30 million people in less than a year," Gates $4 for Business Insider earlier this year. "And they say there is a reasonable probability the world will experience such an outbreak in the next 10-15 years."
Gates is right about the gravity of that threat, according to experts in the field.
George Poste is an ex officio member of the $4, a group created to assess the state of biodefense in the US,.
"We are coming up on the centenary of the 1918 influenza pandemic," he told Business Insider. "We've been fortunately spared anything on that scale for the past 100 years, but it is inevitable that a pandemic strain of equal virulence will emerge."
The 1918 pandemic $4 around the globe, making it one of the deadliest events in human history.
David Rakestraw, a program manager overseeing chemical, biological and explosives security at Lawrence Livermore National Laboratory, and Tom Slezak, the laboratory's associate program leader for bioinformatics, also agree with Gates.
"Both natural and intentional biological threats pose significant threats and merit our nation's attention to mitigate their impact," they told Business Insider in an email.
It's possible that a major outbreak could be intentionally created as the result of a biological weapon, but Poste thinks a serious bioterrorism attack is unlikely due to the complexity of pulling something like that off.
It's very likely, however, that a highly dangerous disease would naturally emerge - and the consequences of that pandemic would be just as severe.
Regardless of how a disease starts to spread, preparedness efforts for pandemics are the same, according to Poste. And the recent outbreaks of Zika and Ebola have highlighted the need for more heightened disease surveillance capabilities. We're still getting a handle on the $4 - and it seems like the mosquito-borne disease may be even more severe than we thought.
Experts have long advocated for better ways to recognize emerging threats before they become epidemics or pandemics. Poste also said we need to improve rapid diagnostic tests and get better at developing new therapeutics and vaccines - something Gates highlighted as a weakness in the "Goalkeepers" report as well.
Until that happens, that threat remains far more real than many of us realize.