COVID-19: time to exonerate the pangolin from the transmission of SARS-CoV-2 to humans
From the earliest times, it has been in human nature to look for a culprit (human or animal) during epidemics, which often leads to irrational behaviors aimed at eliminating the threat. With the advent of COVID-19, bats and pangolins were the culprits. However, what was their real role in the process that led to the current pandemic?
The article in which Jordi Serra Cobo, from the UB Biology Research Institute, participates, helps us to unravel the beginning of COVID-19.
The emergence of COVID-19 has triggered much work aimed at identifying the intermediate animal potentially involved in the transmission of SARS-CoV-2 to humans. The presence of SARS-CoV-2-related viruses in Malaysian pangolins, ACE2 receptor polymorphism, and sequence similarities between the Receptor Binding Domain (RBD) of pangolin cells and humans towards the Sarbecoviruses led to propose the pangolin as an intermediate host. However, it was later reported that the binding affinity of the pangolin ACE2 receptor for SARS-CoV-2 was low.
This article provides evidence that the pangolin is not the intermediate animal that caused the human pandemic. In addition, the available data do not conform to the currently proposed overflow model for emerging zoonosis, so this outbreak is unlikely to explain this outbreak. We propose a different model to explain how SARS-CoV-2-related coronaviruses may have circulated in different species, including humans, before the advent of COVID-19.
The closely related sarbecoviruses circulate in different hosts around the world raising the question of the dynamics of emerging zoonosis and the role that wildlife plays. This article teaches us two hypothetical models of emerging zoonosis, the well-known spillover model and an alternative model, the circulation model.
The spillover model theorizes that emerging zoonosis begins as a result of zoonotic pressure (Plowright et al., 2017). In this model, the virus develops in an epizootic stage (epidemic in animals) in an animal population, it reaches the threshold necessary to make the species jump and produce transmission to humans and spread to human populations. Socioeconomic factors and demographic dynamics trigger the epidemic or pandemic spread of the disease (Plowright et al., 2017; Frutos et al., 2020). According to the spill model, the disease already exists in the human epidemic as an epizootic and, therefore, the identification of the animal reservoir is essential to stop the viral spread.
In the proposed circulation model there is no requirement for zoonotic pressure or epizootic episode before the onset of a human disease. According to the circulation model there is a wide circulation of viruses in different species, including the human one, but without any epidemic occurring. This is consistent with the observation that humans have been much more exposed to various viruses than expected and without any related epidemics (Pike et al., 2010).
According to the circulation model, what really prepares an epidemic is simply an accidental event, that is, a mutation, recombination in the virus genome. The virus is already present in an animal population close to humans or even in humans, and this mutation makes it more invasive and / or pathogenic. This has recently been reported in SARS-CoV-2 (Korber et al., 2020) and beyond coronaviruses has been observed in influenza viruses, chikungunya or Zika (Webster et al., 1982: Tsetsarkin and Weaver, 2011 ; Yuan et al., 2017).
The real triggers of the epidemic and the pandemic are the destruction of territories and natural habitats causing an increase in contacts between humans and animals and the areas of amplification of these contacts such as markets, international trade, mobility, etc. (Pike et al., 2010; Frutos et al., 2020). One of the main positive effects of the circulation model is that the focus is on these human activities and not on wildlife. Pangolins, bats and other animals are not responsible for epidemics or pandemics that affect humans. We need to rethink how we interact with nature. Blaming wildlife for emerging zoonoses can be highly damaging, a massacre and the loss of biodiversity.
More information in the article:
Roger Frutos, Jordi Serra-Cobo, Tianmu Chen, Christian A. Devaux.COVID-19: Time to exonerate the pangolin from the transmission of SARS-CoV-2 to humans. Agust2020