For the last week or so, the world has been watching with horror the Chinese city of Wuhan, the epicenter of a new viral disease outbreak. The catchily-named 2019-nCoV is a coronavirus, one of a very large family, but this particular version is very new (in fact, genetic research is suggesting that it might be only a few months old, having evolved by spontaneous mutation late in 2019). However, Coronaviruses themselves are nothing new – they are in fact ubiquitous, and most species of animals seem to have their own. So, what do we know about coronaviruses? Where did this one come from? And what’s the impact, especially on animals, likely to be?
What is a coronavirus?
A coronavirus is a relatively large viral particle, containing genetic information (essentially, the blueprints to build copies of itself) coded as RNA (ribonucleic acid). We therefore call it an “RNA-virus”.
Like all viruses, it isn’t strictly speaking alive. In fact, it’s probably best to think of it as a self-replicating machine. When the viral particle is passively breathed in, or ingested, by a potential host, protein strands on its outer casing “lock on” to proteins on the cells of the host animal (or person). If they’re able to bind effectively, then they can infect the cell.
Once inside the cell, the virus hijacks the cell’s own systems to make sure that its genetic material is replicated, and new protein cases are made. Once the cell has made many thousands or millions of new viral particles, it bursts, releasing those viruses to spread – either to new cells in the same host, or to new host animals.
However, like most viruses, coronaviruses are usually host-specific, and often target-specific. In other words, they only have the protein machinery to attack certain types of cells, in certain types of animals. Thus, we have Canine Coronaviruses (that affect dogs), Feline Coronaviruses (cats), Porcine Coronaviruses (pigs), and so on.
Why do there seem to be so many forms?
Simply put, because the virus really isn’t very good at replicating itself! Coronaviruses use RNA as their genetic material instead of DNA (like we do). This causes some complications in how they copy their genes (see here for details of how that works!), but more importantly, RNA is much more unstable than DNA. As a result, it mutates much more quickly than many other viruses. This means that each outbreak is slightly different, with the virus changing its structure more or less at random.
It also means that coronaviruses periodically mutate to become more infectious, or less so. However, the more infectious types tend to out-compete the less infectious ones, so over time, they tend to become more infectious, not less. Sometimes, too, they mutate to jump into a different species – and that’s probably what happened in Wuhan last year.
What do coronaviruses do?
It does of course depend! However, in general, coronaviruses attack either the respiratory tract or the gastrointestinal tract.
In domestic animals, we tend to think of them as being more gastrointestinal – Canine Coronavirus, Feline Coronavirus, Calf Coronavirus and Rabbit Coronavirus are all associated with, usually, mild and self-limiting diarrhoea. However, because they mutate so fast, constant reinfection is almost inevitable without excellent hygiene and quarantine procedures.
However, there are also a range of respiratory forms. In particular, respiratory coronaviruses are fairly commonly seen in pigs (Porcine Respiratory Coronavirus, PRCV) and cattle; and of course humans, including many strains of the common cold.
However, occasionally a form of coronavirus may mutate to become much more dangerous. This occurs sometimes in cats, leading to Feline Infectious Peritonitis. In dogs, there are reports of “mutant” highly pathogenic coronaviruses, and in humans, some of the novel coronaviruses have proved deadly, especially SARS and MERS.
So far, the 2019-nCoV (the Wuhan strain) appears less deadly than SARS, but much more dangerous than the common cold. The numbers suggest a mortality rate of 2.7% of confirmed cases; but there are worrying reports that the disease might be mutating.
Where did it come from?
Like most new or “emerging” diseases, the new coronavirus strain appears to be a zoonotic infection – in other words, a disease of animals that has jumped to humans. Of the major epidemics of the last 20 years, this was the source of SARS, MERS and Ebola – and now, it seems, the Wuhan coronavirus.
Part of the issue may be the traditional “Wet” or “Warm Meat Markets”, where livestock and wildlife of a huge range of species are gathered from a wide area, housed together and then slaughtered for fresh meat. This means that species that normally wouldn’t spend time together are forced into close proximity; also, potentially, in a highly stressed state. Now, generally speaking, stressed animals shed more viral particles than relaxed ones, so this isn’t a great mix! These environments are perfect petri dishes for viruses to evolve into forms that jump the species barrier.
In fact, there is some evidence that the 2019-nCoV strain has managed to jump species twice within its recent evolutionary history (so the last few months or maybe years). Researchers have suggested that it includes elements characteristic of both bat and snake coronaviruses.
Why is it spreading?
As you’d expect, humans have no natural immunity to a brand-new virus. So most, and probably all, of the population is immunologically naive – i.e. we have no antibodies against it.
We can express the rate of infection as the R0 value – the number of people each patient would be expected (on average) to infect. So far, estimates place this Wuhan virus at 2.6. For comparison, the pandemic flu in 1918 that swept the world at the end of the First World War had an R0 of about 2.0, making this disease significantly more infectious (although so far, fortunately, much less deadly).
Can it infect animals?
Bottom line – we don’t know! Usually, we’d say it’s pretty rare for a human virus to jump to animals (we call this an anthroponosis). However, this coronavirus has already jumped species at least once, probably twice, in a matter of months. As a result, the possibility does exist.
What is the end result going to be?
In all probability, the epidemic will “fizzle out”. Most epidemic diseases burn out because people isolate themselves from others, and the virus has nowhere to go. The Chinese government’s massive quarantine action should help this – and people’s natural fear of disease will be even more effective. On top of that, the vast majority of those who have been most seriously affected have had underlying health problems. Fortunately, this does not seem to be anything like as bad as, for example, Ebola or SARS.
So is it likely to lead to mass death and disaster?
No, probably not – there’s every chance that this time we’re going to be lucky. That said… infectious diseases like this are inherently unpredictable, so keep an eye on the news headlines.
But if we keep encroaching on wildlife, destroying their environment, and dragging stressed wildlife across countries before penning them with huge numbers of other species, before slaughtering and eating them fresh, it’s only a matter of time before something much nastier does emerge.
If you’re worried about your pet’s health, contact your vet for advice. If you’re worried that you might have been exposed to the new coronavirus, please seek urgent medical attention.