Teddies Talks Biology - Issue 9

Lucy Draper—LVI

A Zoonosis is a disease that is transmitted from an animal into a human. The disease is usually either bacterial, viral, fungal or parasitic. These diseases are then transmitted via either vec- tors, bites or saliva into the human body. Examples of such diseases would be Rabies and Lymes Disease. Once inside the human body, pathogenesis occurs: this describes replication in the host. The success of the replication can be affected by host immunity, defence factors and cell/organ specific receptors. Replication of an animal virus within the first human host is a key turning point in the zoonotic process, as it leads to the mutation and evolution under selective restraints of the body If successful, and there is a high virus titre (large quantity of virus in a given volume) it means that spread to another human is possible, therefore initiating selection for variants with in- creased capacity to spread in the human population. How the Covid virus moved from animal to human populations is yet to be determined, however there has been speculation amongst the scientific community about how it was transferred across the populations.

Dr. David Robertson, head of viral genomics and bioinformatics at the University of Glas- gow, found that the closest ancestor of Covid - 19 had been living in bats already for up to 70 years prior, and that despite the lack of clarity of what happened between bats and humans it is very likely that the virus circulated for a while in a pangolin or another intermediary an- imal. His research on the virus ’ s genetic code proves beyond a shadow of a doubt that the

virus originated in nature, therefore highlighting that the transmission could be classified as a zoonosis, as long as it can be proven that the transmission occurred through either an interme- diary animal or a bat itself—which even experts disagree on.

However, it is clear that the virus has required no significant adaptations since the start of the pan- demic, this shows that the virus, which naturally evolves in bats, was almost immediately ready to be spread through human contact. Thus showing how it contained properties which were conducive to human infection already, regardless of how it originally transferred to humans. In research un- dertaken by J. Mackenzie and D. Smith the Angi- otensin - converting enzyme 2 (ACE2) was known to be the cell receptor (the molecule which let the virus into the body) for other coronaviruses. The receptor - binding domain for Covid - 19 was suffi- ciently similar to this, indicating that Covid - 19 could successfully use human ACE2 for receptor

entry into cells, showing that it would have always been highly transmissible whether it emerged into the human community by bats or otherwise. In all, the pandemic could be classi- fied as a zoonotic disease, however, no animal reservoir has yet been found, so the classifica- tion could be described as premature. Instead, it could be called an ‘ emerging infectious dis- ease ’ (EID) of probable animal origin until the real cause is found, if ever.

Teddies Talks Biology I Issue 9 I June 2021

6