THE VIRUS DETECTIVES

WORD BEGAN TO SPREAD LATE on 10 January this year. A file containing only a few hundred lines of genetic code had just appeared on a public database run by the National Institutes of Health in the US. It had been uploaded by a small team of researchers in China. Within hours, virologists were collectively poring over these few meagre kilobytes of data with wary curiosity. What they saw worried them deeply.

Several days earlier, troubling news had emerged from Wuhan, in central China – an outbreak of several cases of viral pneumonia linked to a local seafood market. The world media, ever primed for news of an emerging bird flu, took some notice. But with raging bushfires in Australia, a presidential impeachment in the US and Brexit competing for the world’s attention, the mystery virus only garnered modest interest.

For those who know viruses, however, something wasn’t quite right. By early January, official reports announced no evidence of significant human-to-human transmission. Yet, by 1 January there were already 40 confirmed patients, and 59 by the 9th. Even in the confines of a crowded marketplace, this seemed high for all the cases to have emerged from contact with the same animal. Then there were the symptoms: a fierce fever coupled with the onset of a persistent dry cough and breathlessness, and rapid progression to pneumonia. Bacteria were ruled out – it wasn’t a new superbug. Influenza was also eliminated – this wasn’t bird flu. Soon, staff in Wuhan’s major hospitals were trying to raise the alarm: this illness looked a lot like SARS.

In 2003, Severe Acute Respiratory Syndrome spread through China’s Guangdong Province. By the time it had run its course it had reached 26 countries and infected more than 8000 people; 774 had died.

The SARS virus (SARS-CoV) was a coronavirus, which most likely crossed the species barrier from bats. Coronaviruses are common in the animal kingdom, but historically they haven’t caused humans much bother. In fact, until 2003 only four strains were circulating in the human population; all tended to cause only mild common-cold symptoms. But in many of those infected, SARS-CoV caused severe disease, including extensive damage to lungs and other organs. In 2012 another corona-virus – Middle East Respiratory Syndrome (MERS) – made the leap from camels to humans. MERS was less contagious than SARS but far more lethal. Of only a few thousand cases, almost four out of every 10 patients have died.

So when the SARS-like pneumonia appeared in Wuhan, Chinese scientists worked quickly to isolate the virus and sequence its genome. Soon they had it. It was indeed a coronavirus.

The genome sequence was made public, and immediately genetic sleuths began to scrutinise it with their well-honed algorithms, comparing it to known coronaviruses, searching for mutations. The