Coronavirus as Zoonosis

Transferring from wild animals to humans


An outbreak of a new coronavirus, also known as SARS severe acute respiratory syndrome -CoV coronavirus -2, started in December 2019 in the Wuhan region of China. The virus can cause the disease COVID-19.

In the case of SARS and this coronavirus outbreak, bats were most probably the original hosts. They then infected other animals via their poop or saliva, and the unwitting intermediaries transmitted the virus to humans.

“Poorly regulated live-animal markets mixed with illegal wildlife trade offer a unique opportunity for viruses to spill over from wildlife hosts into the human population,” the Wildlife Conservation Society

A new coronavirus that originated (as of December 2019) in Wuhan, China, is currently spreading around the world at breakneck speed. Obviously, attention is now focused on mitigating risks to people, with the result that travel is limited to at least delay further spread.

But there is a link between the sudden onset of this virus and wildlife. Very soon after the virus was discovered, Chinese scientists tried to trace the origin of the virus.

January 30, 2020, so already after two months after discovering the virus, they published the results of their research in the journal The Lancet

It is also important for veterinarians to take note of this article, as well as of the studies published later. Attempts will be made to regularly update this page with new information that is relevant to veterinarians.

Genomic characterization and epidemiology of 2019 novel coronavirus: implications for virus origins and receptor binding, Roujian Lu * et al, Lancet 2020; 395: 565–74, Published Online January 29, 2020


In late December, 2019, patients presenting with viral pneumonia due to an unidentified microbial agent were reported in Wuhan, China. A novel coronavirus was subsequently identified as the causative pathogen, provisionally named 2019 novel coronavirus (2019-nCoV).

Phylogenetic analysis of 2019-nCoV, sequenced from nine patients' samples, showed that the virus belongs to the subgenus Sarbecovirus. 2019-nCoV was more similar to two bat-derived coronavirus strains, bat-SL-CoVZC45 and bat-SL-CoVZXC21, than to known human-infecting coronaviruses, including the virus that caused the SARS outbreak of 2003.

This finding suggests either possible droplet transmission or that the patient was infected by a currently unknown source.

To find out the source, research was conducted into similarities between the first infected people and the locations visited. It showed that several patients with viral pneumonia were found to be epidemiologically associated with the Huanan seafood market in Wuhan, where a number of non-aquatic animals such as birds and rabbits were also on sale before the outbreak. Eight of the patients had visited the Huanan seafood market before the onset of illness, and one patient (WH04) did not visit the market but stayed in a hotel near the market.

Phylogenetic analysis showed that bat-derived coronaviruses fell within all five subgenera of the genus Betacoronavirus. Moreover, bat-derived coronaviruses fell in basal positions in the subgenus Sarbecovirus, with 2019-nCoV most closely related to bat-SL-CoVZC45 and bat-SL-CoVZXC21, which were also sampled from bats. These data are consistent with a bat reservoir for coronaviruses in general and for 2019-nCoV in particular.

However, despite the importance of bats, several facts suggest that another animal is acting as an intermediate host between bats and humans.

  1. the outbreak was first reported in late December, 2019, when most bat species in Wuhan are hibernating.
  2. no bats were sold or found at the Huanan seafood market, whereas various non-aquatic animals (including mammals) were available for purchase.
  3. the sequence identity between 2019-nCoV and its close relatives bat-SL-CoVZC45 and bat-SL-CoVZXC21 was less than 90%, which is reflected in the relatively long branch between them. Hence, bat-SL-CoVZC45 and bat-SL-CoVZXC21 are not direct ancestors of 2019-nCoV.
  4. in both SARS-CoV and MERS-CoV, bats acted as the natural reservoir, with another animal (masked palm civet for SARS-CoV and dromedary camels for MERS-CoV) acting as an intermediate host, with humans as terminal hosts.


on article The Lancet january 29, 2020

No hard evidence has been found in this study that the virus indeed originates from bats. Only the relationship between the examined patients and their visit to a Sea-food market suggests that the virus has spread to humans via this market.

On the basis of current data, it seems likely that the 2019-nCoV causing the Wuhan outbreak might also be initially hosted by bats, and might have been transmitted to humans via currently unknown wild animal (s) sold at the Huanan seafood market.

Since it could be ruled out that there was a direct jump from bats to humans (at that time the bats were also in hybernation in China), it must be assumed that the virus had established itself in an intermediate host. It follows from other studies that this may most likely have been a mammal also traded on the said market.

More generally, the disease outbreak linked to 2019-nCoV again highlights the hidden virus reservoir in wild animals and their potential to occasionally spill over into human populations.


A study of cultured bat cells shows that their strong immune responses, constantly primed to respond to viruses, can drive viruses to greater virulence. Modeling bat immune systems on a computer, the researchers showed that when bat cells quickly release interferon upon infection, other cells quickly wall themselves off. This drives viruses to faster reproduction. The increased virulence and infectivity wreak havoc when these viruses infect animals with tamer immune systems, like humans.


Bats have a strong developing immune system. This is probably connected to their highly active metabolism.

It is almost impossible that the viruses that bats carry, are directly transferred to humans. It follows from the various studies that it was almost always possible to demonstrate that an intermediate jump was required via a different animal species.

Destroying bats for fear of viruses is questionable. It is better to limit the possible jump between the virus in animals toward humans by ending uncontrolled and illegal trade and markets where live wild animals are sold.

Which animal is the most likely intermediate: There is no conclusive study which proves that one kind of animal could have been the stepping stone in transferring the virus from bats to humans. Depending on studies and kind of similar virusses there are different suspects, such as camels, civet, but also an unexpected suspect the Pangolin. Not only local species (if available), but also probably the poached species of African Pangolin. However, can there be any proof that this animal (either live of dead) coult be the intermediate-species in Wuhan China?  

What about the Pangolin


26 FEBRUARY 2020

Mystery deepens over animal source of coronavirus

Pangolins are a prime suspect, but a slew of genetic analyses has yet to find conclusive proof.

Not close enough!

Three similar comparison studies were posted on bioRxiv. One of those papers — by an international research group , posted on 18 February — found that coronaviruses in frozen cell samples from illegally trafficked pangolins shared between 85.5% and 92.4% of their DNA with the virus found in humans. Two other papers published on 20 February, from groups in China, also studied coronaviruses from smuggled pangolins. The viruses were 90.23%3 and 91.02%4 similar, respectively, to the virus that causes COVID-19.

The genetic similarity should be higher than reported in these studies before the host can be identified, says Arinjay Banerjee, who studies coronaviruses at McMaster University in Hamilton, Canada. He notes that the SARS virus shared 99.8% of its genome with a civet coronavirus, which is why civets were considered the source. If pangolins are the origin of the current outbreak, says Banerjee, it is not the pangolins in these studies.

Key differences

So far, the closest match to the human coronavirus has been found in a bat in China’s Yunnan province. A study published on 3 February found that the bat coronavirus shared 96% of its genetic material with the virus that causes COVID-19. Bats could have passed the virus to humans, but there are key differences between the RBD sites in the two viruses. This suggests that this specific bat coronavirus did not directly infect people, but could have been transmitted it to people through an intermediate host, say researchers.

The papers raise more questions than they answer, says Jiang Zhigang, an ecologist at the Chinese Academy of Sciences Institute of Zoology in Beijing. He asks, if pangolins are the source of the virus, and they came from another country, why haven’t there been reports of people being infected in that location?

Sara Platto, who studies animal behaviour at Jianghan University in Wuhan, worries that all the speculation about pangolins being the source could drive people to kill them. Civets were killed en masse after the SARS outbreak. “The problem is not the animals, it’s that we get in contact with them”