Amid reports of a mysterious respiratory illness spreading among children in China, an expert explains how regularly unexplained outbreaks turn up.
It began one spring morning in 1993, when a Navajo family pulled into a service station in New Mexico and dialled 911. Their son, a 19-year-old marathon runner, had suddenly developed breathing problems. He was rushed to the local hospital by ambulance, where he died. The doctors were stumped – what could have killed someone so young and healthy?
It soon transpired that the marathon runner’s death was not an isolated incident. He had been on the way to his fiancée’s funeral, after she had succumbed to a similar respiratory illness just a few days earlier.
Each time reports of a mysterious new outbreak hit the headlines, there is no shortage of possible suspects. There are more viral particles on Earth than stars in the Universe, and 10 times more bacterial cells in our bodies than mammalian ones. In total, our planet is home to an estimated one trillion species of microorganisms. But only 1,513 types of bacteria, 219 viruses, 300 parasitic worms, 70 protozoa, and 200 fungi are currently known to cause disease in humans. The rest are waiting to be discovered.
How common are mystery outbreaks?
“There are clearly some outbreaks that are still mysteries,” says Stephen Morse, professor of epidemiology at Columbia University Irving Medical Center in New York.
In the case of the Navajo couple in 1993, the local medical investigator noticed that there had been other cases of this unexplained sickness in the preceding weeks. They had all occurred within the Native American community in the Four Corners region of the south-western US.
With more cases appearing each week, the race was on to catch the culprit. But it would be another two months before it was identified as hantavirus pulmonary syndrome, caused by a totally new kind of hantavirus – a group of viruses which usually infects rodents.