In just a couple of months the new coronavirus that emerged from the Chinese city of Wuhan has spread around the world, sparking a race to find treatments and vaccines against it.
The human race is locked in a battle against something five million times smaller than us. The novel coronavirus that has emerged from the Wuhan in China has gone from an unknown enemy to feared worldwide, in a matter of months.
As it continues to spread around the world, bringing panic with it, scientists are striving to develop ways of fighting this previously unknown threat. Sophisticated computer modelling is being used to track and predict its transmission, while virologists are attempting to engineer a vaccine. Others are seeking drug treatments that can help those who fall ill with the infection.
But this is not the first coronavirus scientists have encountered, and defeating them is harder than you might think. Even after decades of trying, coronaviruses are formidable foes.
Some of the most common and challenging diseases are caused by coronaviruses. One of the viruses that causes the common cold is a coronavirus, and we have yet to find an effective vaccine or cure for it despite years of work. Both the deadly Severe Acute Respiratory Syndrome (Sars) and Middle East Respiratory Syndrome (Mers) outbreaks were also caused by coronaviruses.
They all belong to a large group of viruses that can infect both humans and animals and can occasionally jump the species barrier. Mers, for example, was first reported in 2012 when a young boy was infected after close contact with a camel. Since then, there have been many reported cases of people being infected by camels.
The new coronavirus, which has been provisionally named 2019-nCoV, appears to be a young virus that may have emerged sometime in early December, according to attempts to trace its origins. Based on analysis of its genetic code, 2019-nCOV was initially thought to have jumped to humans from bats. The human virus has been found to share many genetic similarities to two coronaviruses in bats, but others have suggested it may have come from snakes, although this idea has been widely dismissed by virologists.
Most recently, endangered pangolins, whose scales are heavily used in Chinese traditional medicine, are being proposed as a likely conduit for the virus. Some researchers have proposed that a bat coronavirus may have combined with another coronavirus in pangolins to produce the strain now infecting humans.
But while the first cases likely occurred in people who had close contact with infected animals, it seems that most new cases from this 2019-nCoV are being passed human to human. “We believe it came from a local market, and that market is now closed,” says Christl Donnelly, a statistical epidemiologist working at Imperial College London and Oxford University. “So, it certainly is being maintained by human transmission.”
Coronaviruses typically target the upper respiratory tract, causing a range of illnesses which can potentially include pneumonia. But there is growing evidence they can move further down the body, and also affect the central nervous system, causing long-term neurological damage.
The name coronavirus itself derives from the Latin for crown, because they are sphere-shaped but covered in spikes, which resembles a crown.
Contained within this prickly shell is a string of single-stranded genetic code called RNA. As they spread from host to host, this RNA code can become easily jumbled, allowing coronaviruses to mutate quickly. This increases the chances of them gaining the ability to switch species as well as alter other characteristics, such as how infectious they are and the severity of illness they cause. It is also why so many new kinds of coronaviruses keep cropping up. It’s also why they are so hard to fight – it’s hard to hit a constantly changing target with vaccines and drugs.
In order to get a reliable model of how the disease spreads, Donnelly says, there are a few things we need to know about the virus. First, how long someone might be infected by it before developing symptoms. This is called the incubation period. Second, we need to know how long someone with the virus remains infectious for, and in cases where patients do not recover, how quickly the virus can cause death. “That helps us estimate the case fatality rate,” says Donnelly.
Another important factor is the reproduction number, which is how many other people someone with the disease will infect. Donnelly and her colleagues have estimated the new coronavirus to have a reproduction number of about 2.6. “If that number is greater than one, then you expect there to be an outbreak,” she says.
There can be great variation in the number of people a patient might infect. One patient with the new coronavirus, for example, infected 14 health care workers. These individuals are classed as “super spreaders”, and are responsible for a disproportionate share of the spread of the disease. This is because in a cough or sneeze they shed far larger numbers of the virus particles than other patients, increasing the chance they will infect someone else.
This presents a particular challenge when trying to contain an outbreak. A super spreader can enable diseases to spread faster. Both the Sars and Mers outbreaks were complicated by the role of super spreaders.
But identifying exactly who a super spreader is can be difficult. Who becomes a super spreader is both a combination of their own biology, the virus itself and the environment they are in. Some people’s immune systems allow them to carry the virus with few or mild symptoms. This means they will often move around and even travel long distances with the virus. Others, however, can suffer the opposite – heavy symptoms that cause them to sneeze and cough a lot, and so spread the disease more to those around them.
General precautions such as wearing face masks, hand-washing and stringent quarantine procedures can help to limit the spread.
New technology is also making it easier to diagnose specific viruses in the first place, which will help efforts to not only contain the outbreak, but also make it easier to understand how it spreads. Around the world, scientists are trying to develop new rapid diagnostic tools that can be used. The US Center for Disease Control and Prevention (CDC) has released a DNA based diagnostic kit for the new virus that can produce results in around four hours, but needs expensive laboratory equipment to work. Researchers at the University of California, San Francisco, and a number of biotechnology companies are reportedly working on faster approaches that do not require specialised equipment.
Even if it can be diagnosed quickly, finding an effective treatment for a virus like this is famously difficult.
The main way of treating a viral infection is to find small molecules that prevent the virus from replicating inside our cells. These “antivirals” interfere with the virus’s ability to enter our cells, disrupts its ability to hijack our cellular machinery to replicate, or prevents it from escaping infected cells.