The Wuhan strain
The coronavirus has now spread from China to at least 25 countries. How worried should we be?
Where did the virus come from?
Originally, probably from a bat-infested cave in rural China; bats serve as reservoirs for many dangerous diseases (see box). The Wuhan virus is a coronavirus, of a type previously unknown: hence, its name, 2019-nCoV (2019 novel coronavirus). Rapid genetic sequencing has shown that it shares 96% of the genome of a coronavirus derived from bats. It is almost certain that the epidemic among humans began at the Huanan “wet market” in the city of Wuhan. Half of the initial victims were linked to this market, where an array of live wild animals were on sale for food and medicinal purposes. Although bats are eaten in some parts of China, in this case, the virus probably passed through another wild creature – possibly a snake, a porcupine or a bamboo rat, but more likely, a rabbit or a bird.
What exactly are coronaviruses?
A group of viruses discovered in the 1950s, which cause disease in mammals and birds. They get their name because they have viral spikes on their surface which resemble a crown, or corona. They are one of the main causes of upper respiratory infections in humans, usually in the form of the common cold, but sometimes in far more dangerous forms, such as severe acute respiratory syndrome (Sars), which broke out in China in 2003, and Middle East respiratory syndrome (Mers), first seen in Saudi Arabia in 2013. Both are closely related to 2019-nCoV, and also originated in bats, though both reached humans via, respectively, civet cats and camels (Mers is known as “camel flu”). These viruses become particularly dangerous when they mutate so they can spread from human to human. The body has no natural immunity to novel viruses; there are also no vaccines, and no specific treatments.
What does 2019-nCoV do to the body?
A study in The Lancet of the clinical effects of 99 hospitalised patients (i.e. severe cases) in Wuhan showed that around 80% had a fever and a cough; 30% had shortness of breath. Threequarters had bilateral pneumonia, a severe inflammation in both lungs. The attack on the lungs is what does the damage: 17% of patients developed acute respiratory distress syndrome, and 11% of the 99 died as a result of multiple organ failure. The virus seems to particularly affect older men with existing medical conditions. Although it’s hard to be sure yet, the overall death rate – including patients who aren’t hospitalised – appears to be relatively low, at around 2%: Sars has a fatality rate of 9.6%; Mers of around 34% (seasonal flu is about 0.13%, Spanish flu was 10-20%, Ebola is 50%). But the fatality rate is only one of the factors which dictate how bad the outbreak will be.
What are the other factors?
Crucially, how contagious it is. Scientists judge this by how many people, on average, each infected person passes it on to – its reproduction number. Early estimates suggest that 2019-nCoV’s number is similar to that of Sars – between 1.5 and 2.5 – and that it is spread in a similar way, mainly via respiratory droplets produced when an infected person coughs or sneezes. However, it has already infected a much larger number than Sars, probably because – unlike Sars, a brutal disease – it’s often hard to spot: most sufferers have mild cold-like symptoms. It has a long incubation period, of up to 14 days, which has increased the geographical spread. Chinese officials had believed that people could even spread the virus before they had symptoms, but recent research suggests that this is not the case.
How can the virus be stopped?
Research on a vaccine was under way within hours of the Chinese authorities sharing the genetic code round the world. In the wake of the Ebola virus, the Coalition for Epidemic Preparedness Innovations (Cepi) was set up to accelerate vaccine production, and it is funding three separate vaccines. Even so, this will take at least six months. In the meantime, the main hope lies in identifying infected individuals and isolating them before they infect others, along with “contact tracing”: finding everyone they might have infected. This is how the Sars epidemic of 2002-3 was stopped. However, despite China’s imposition of effective quarantine on Wuhan, the disease appears still to be spreading, perhaps because the city of 11 million people is so well connected: it is one of China’s four key railway hubs, with a large international airport.
Why is China vulnerable to such viruses?
Because of the size and density of its population, and their close contact with animals harbouring viruses. At least 60% of emerging infectious diseases reported around the world are zoonotic: they are communicated to humans by animals, and the frequency of such transmissions has been increasing fast. China’s wet markets provide a particularly ripe opportunity for such “viral exchange”, but it’s part of a global pattern.
What is that global pattern?
The modern world is well designed to spread such viruses. Populations are expanding and exploiting wild ecosystems which harbour animals carrying unknown viruses – recent examples include Ebola, Zika, HIV and Nipah. Intensive farming also provides opportunities for viruses such as swine flu to develop. Trade takes these into densely populated areas, which are ideally designed for incubation and linked to other populated areas. Luckily, medicine and global public health planning have taken great strides over the past decade. Health officials (and journalists) are often accused of fearmongering, and the odds are that the coronavirus, like Sars and swine flu, will be contained. But we just don’t know. Viruses mutate: whether it’s 2019-nCoV or the next one, there is a very real threat of a pandemic virus emerging with a devastating mix of virulence and infectiousness.