Viruses that jump from animals to humans, known as zoonoses, have existed for centuries, but experts say outbreaks of dangerous new diseases with the potential to become pandemics are on the rise. Indeed, they have become four times as frequent in the past half-century.
Since the 1970s, it is estimated at least three dozen infectious diseases have emerged from human interference with animals, including Sars, Mers, Ebola, bird flu, swine flu and the Zika virus. As far back as 2007 the World Health Organisation warned that infectious diseases were emerging at a rate that had not been seen before.
The spread of the viruses is put down to a deadly combination of wildlife trafficking and consumption, increasing human encroachment into wildlife habitats as more people live in densely populated areas – and air travel, which enables pathogens to take hold globally.
Three years ago, an article published by the US National Centre for Biotechnology Information stated, presciently: “The Aids and influenza pandemics have claimed and will continue to claim millions of lives. The recent Sars and Ebola epidemics have threatened populations across borders. The emergence of Mers may well be warning signals of a nascent pandemic threat.”
Zoonotic diseases are complex, and it’s sometimes impossible to say a virus has disappeared, because it might have many different strains, and might mutate and lie dormant. This is a timeline of the main zoonotic diseases to have hit us since the start of the 20th century:
The 1918 flu pandemic: This was the most severe pandemic in modern times, killing at least 50 million people in two years. It is widely believed that the virus originated in birds because it shared genetic mutations with the bird flu virus later found in Asia, and could have transferred to horses in the trenches of the first world war before spreading to humans. This is disputed, with one study suggesting it came from mammals.
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