While it’s impossible to calculate the odds of a disease wiping out humanity (Are they better or worse than an asteroid hitting earth? What about a robot uprising?), this staple subject of both page and screen contains a kernel of truth. There are diseases out there in the world that pose a substantial risk to humankind. There are diseases that have attacked us already, killing millions upon millions. What follows are five diseases that, given the perfect, deadly mutation and the right push could lay siege to humanity.
And at the the end of this list there’s a kind of bonus: a disease that once would have been listed here, which ravaged humankind, killing upwards of 300 million people in the 20th century alone. But decades ago humanity struck back, eradicating it from the face of the earth.
It’s believed that flu pandemics have occurred throughout human history, when especially nasty strains of influenza virus spread globally. The deadliest of these waves that we know about was the 1918 “Spanish” flu outbreak that according to flu.gov infected between 20 and 40 percent of the worldwide population and killed approximately 50 million people. With its high mutation rate and ability to spread easily, the flu virus remains a constant risk to humanity. Just as recently as 2009, the H1N1 strain of flu is believed to have killed hundreds of thousands of people.
While the flu shot is not perfect – this year’s version was less effective for the elderly for reasons that are unclear – the CDC recommends that everyone over the age of six months old get a flu shot.
One of humanity’s best weapons against infectious disease could ultimately be the cause of a major threat to us: Superbugs. Superbugs are bacteria that have become resistant to antibiotic drugs. Recently, Sally Davies, the U.K.’s chief medical officer, described the danger posed by antibiotic-resistant bacteria as “apocalyptic.”
“There are few public health issues of potentially greater importance for society than antibiotic resistance,” Davies told the UK newspaper The Guardian.
The types of bacteria that have become untreatable by antibiotics range from strains of staphylococcus, a common bacteria that usually causes minor skin infections, if anything, to the sexually-transmitted disease gonorrhea. And experts warn that there are not enough new antibiotics coming to market for humanity to keep up in this evolutionary arms race.
The good news is that Ebola appears to be a blood-borne pathogen, making it significantly more difficult to transmit than air-borne diseases like the flu. The bad news is that the virus’s “natural reservoir” – the animals it calls host when it’s not cutting down humans – is unknown (scientists reportedly think the likeliest candidate is bats).
This respiratory disease caused by the SARS coronavirus came to the public’s attention in 2003, with a concerted public awareness campaign conducted by health organizations around the world. The name stands for Severe Acute Respiratory Syndrome, and the disease demonstrated, according to the Mayo Clinic, “how quickly infection can spread in a highly mobile and interconnected world.”
The 2003 outbreak spread to more than two-dozen countries, infecting about 8000 people worldwide, according to the CDC. The disease killed approximately 10 percent of the people infected, according to Harvard Magazine, and, because its symptoms mimicked that of the cold of flu, experts worried it would spread undetected. Ultimately, the spread of the disease was curbed by an aggressive public health campaign, but, worryingly, a different coronovirus has emerged in recent months, and has caused six confirmed fatalities.
The disease comes in three types, depending on how one catches it, according to the CDC. It can infect the skin, the gastrointestinal tract, or, in its most deadly form, the lungs. About half the cases of inhaled anthrax result in death.
The success story on this list – as far as humanity is concerned, anyway – smallpox is the only disease that has been driven extinct due to a concerted effort by humankind (although the guinea worm could be next). This killer of millions was known throughout much of human history – and is believed to have been responsible for one-third of all cases of blindness until its eradication. It was vanquished in 1980 through a vaccination campaign headed by WHO. Smallpox caused severe rash, sores and fever and killed nearly a third of those who contracted it before it was wiped out.
Perhaps there’s reason to be (cautiously) optimistic. But there are a couple of samples stashed away for government research.