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25
Jan

On the relationship of bats with the outbreak of acute respiratory disease caused by a new coronavirus in Wuhan (China)

Recently the news of an epidemic outbreak of acute respiratory disease caused by a new coronavirus declared in Wuhan (China) has been reported to the press. Today, hundreds of cases have been registered, including some imported in several countries. At the present time, WHO has not declared the international emergency situation but has made recommendations to avoid a possible internationalization of the outbreak and in any case it will be updating the information regularly, to which it will be necessary to be attentive.

The first epidemiological investigations have shown that the origin of the outbreak is linked to a market of shellfish and wild animals, so it is assumed that the most likely source must be an animal still to be determined from among those sold there, since Emerging diseases usually have their origin in infectious agents typical of animals, which successfully adapt to humans by acquiring the ability to transmit from person to person. In addition, there is a precedent for the outbreak of severe acute respiratory syndrome (SARS), declared in 2003 also in China in similar circumstances and which was caused by a coronavirus very similar to the current one, causing more than 8,000 cases and almost 800 deaths in several countries. In this case, the civets appeared to be the animal source of the outbreak, since the virus could be detected in samples of these animals from the market where it originated. In 2012, another outbreak of what later came to be called the Middle East respiratory syndrome (MERS) was declared in Saudi Arabia, which was caused by another dromedary-transmitted coronavirus. To date, 2,494 cases and 854 deaths have already been declared, the vast majority in Persian Gulf countries, although imported cases have also been declared in other countries.

After verifying that the civet could be a source of transmission but was not the natural host of the SARS virus, it began to be searched in other animal species in China, with very similar viruses found in horseshoe bats. Subsequent studies have revealed a great diversity of coronaviruses in bats around the world that do not seem to cause them disease, which is evidence of a good mutual adaptation developed during a long common evolutionary history. This fact has led to propose as a hypothesis (so it remains today) for the emergence of SARS a jump of a species of horseshoe bat to civet and of this to the human being. Among this great variety of bat coronavirus there are also some very similar to the MERS coronavirus, a fact that is interpreted by the WHO in its disease description sheet as “the origins of the virus are not well known but, as can be seen from the analysis from several of its genomes, it is believed that the virus could have originated in bats and had been transmitted to camels at some point in the distant past ”, illustrating how prudence and rigor should prevail when extrapolating general conclusions about evolutionary biology to the investigation of the origin of specific epidemic outbreaks.

The nucleotide sequence of the new coronavirus of 2019 that is currently causing the outbreak shows high homology with a corona coronavirus of the SARS coronavirus group, this being the only fact that relates it to bats, since today the virus still It has not been detected in any animal, although exhaustive studies are being carried out that we hope will bear fruit soon. Finally, the claim that the origin of the outbreak could be in snakes comes from a very speculative study whose conclusions are not very solid and are generating strong criticism in the scientific community.

In consequence:

  1.  It is not at all established today that bats have been the direct source of the outbreak in China. Although the available data based on the study of the virus sequence indicate that bats should be one of the objects of research aimed at unveiling it, we must wait for the results and not make aprioristic statements. ..
  2.  Neither bats nor any other animal already have any role in the progress of the epidemic, which is based exclusively on the transmission from person to person.

Juan Emilio Echevarría 

Virologist

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