On January 30, the World Health Organisation declared the new coronavirus (COVID19) a public health emergency of international concern (PHEIC)
Four years ago, the World Health Organisation established a priority list of pathogens for which more research is urgently needed. All of them are viruses for which there are no vaccines or treatment and that have the potential to cause an epidemic with a considerable number of deaths. Two coronaviruses were already included in this Blueprint List of Priority Diseases: MERS and SARS. A couple of years later, the WHO added the already known Zika virus (due to its severe consequences on babies born to infected mothers) and the so-called “Disease X”, in referral to any new unknown virus that may cause an epidemic.
The prediction of a Disease X, that caused so much intrigue at the moment, seems to have been fulfilled sooner rather than later. A few days before closing 2019, several cases of a mysterious pneumonia were reported in Wuhan, China, all of them related with a market where a multitude of animals, many of them wild, are sold. After eliminating the usual suspects (influenza, MERS, SARS), the medical community realised it was dealing with a new virus belonging to the coronavirus family (to which MERS and SARS also belong). Initially called 2019-nCoV, it has been officially baptised as SARS-CoV-2 and the disease as COVID-19 (as reference to coronavirus disease and the year it was first identified).
The prediction of a Disease X, that caused so much intrigue at the moment, seems to have been fulfilled sooner rather than later
Over the last few weeks, the epidemic has evolved very quickly: over 75,000 confirmed cases by February 20 (most of them in China), and the virus has travelled by plane or cruise ship to more than 20 countries. Fortunately, our knowledge of the virus has also advanced at great steps, and the response (in China and globally) has been much quicker, efficient and transparent than that of SARS in 2002-2003. However, many questions remain, particularly regarding how easily transmissible is the virus (or its contagion rate), if it can be transmitted before infected people develop symptoms, and how dangerous it is (i.e. the case fatality rate). These factors will decide how the epidemic will evolve over the following weeks.
Will there be more diseases X, Y or Z?
The answer is an emphatic “Yes”. Someone once asked me “How come so many new viruses are appearing lately?”. The concept of “new” is very relative. The viruses included in the Blueprint list mentioned above are called emerging because they were identified only recently, after having caused disease in humans. However, these viruses have existed in nature for a very long time, in animal reservoirs.
A rough estimation based on a study in bats suggests that at least 320,000 viruses can infect mammals, and that all species of vertebrates together could host at least 3 million and a half different viruses. If we put together vertebrates, invertebrates, plants, lichens and algae, this number could rise to over 100 million. And this would be without counting the viruses that infect bacteria (bacteriophages). The Nature journal estimated that, if all viruses present on the planet (~1031) were aligned, they would cover a distance of 100 million light years!
The 'Nature' journal estimated that, if all viruses present on the planet (~1031) were aligned, they would cover a distance of 100 million light years!
Knowing that we have only identified around 1,400 human pathogens (including viruses, bacteria, fungi, protozoa and worms), it goes without saying that the number of yet unknown viruses that could one day “jump” to people and cause an epidemic, is overwhelming
While the danger of this happening has always existed, the risk of it occurring is increasing. There are more and more people on the planet, we are invading ecosystems where many animals (and their viruses) live and with which we did not have previous contact, and we are travelling faster and farther. Add climate change, that will lead to a redistribution of many animals (and their viruses) to new habitats.
For now, it is important to identify the animal reservoir of the new coronavirus to try to avoid a similar outbreak in the future - for SARS, the intermediary host between bats and humans turned out to be the civet cat, and a recent analysis suggests that for SARS-CoV-2 it could be the pangolin, an animal often used in Chinese traditional medicine. Another important action will be to limit the capture and sale of wildlife in markets, knowing that at least 320,000 unknown viruses could do the same.