COVID-19: A Zoonotic Disease?
Zoonotic diseases are infectious diseases that are naturally transmitted from animals to humans. The World Health Organization (WHO) specifies that the greatest risk of transmission of zoonotic diseases occurs at the interface between humans and animals, whether through direct or indirect exposure to animals, their food products, or their environment.
Among the most common zoonoses are Leishmaniasis, Leptospirosis, Toxoplasmosis, Rabies, among others, and we could "include" the novel COVID-19 in this list, since the main theory about the origin of the new coronavirus pandemic is that it jumped to humans in a wildlife market in Wuhan, China, at the end of 2019. Some zoonoses are relatively benign, but many are quite harmful, even deadly, as is the case with COVID-19.
Although evidence suggests that bats are a significant reservoir of coronaviruses, a direct link between these coronaviruses and SARS-CoV-2 has not been established, pointing to a possible intermediate host. The hypothesis that the virus originated in a seafood and wildlife market, which was linked to the first cases of the respiratory illness and where the potential intermediate host might have been located, was ruled out shortly after the outbreak began when the market was dismantled. This prevented the search for the animal species that would be the original source of the SARS-CoV-2 coronavirus.
Among the possible intermediate hosts are pangolins, the most commonly trafficked mammals used for both food and traditional medicine . An article published in the journal Nature , titled “Identification of SARS-CoV-2-related coronaviruses in Malayan pangolins , ” revealed coronaviruses detected in a small number of pangolins smuggled into China that are closely related to the SARS-CoV-2 coronavirus. According to this publication, the degree of viral similarity is not sufficient to suggest that pangolins are the intermediate hosts directly involved in the current SARS-CoV-2 outbreak , although the findings suggest they are a secondary host for coronaviruses.
Despite the global impact of COVID-19, which has caused not only health devastation but also economic and social repercussions, the origin of SARS-CoV-2 remains an unsolved puzzle. The Hong Kong virologist In September 2020, Li-Meng Yan published a report with evidence that allegedly proves the virus originated in a Chinese laboratory . The data was published in the scientific journal Zenodo in a paper titled “Unusual features of the SARS-CoV-2 genome that suggest sophisticated laboratory modification rather than natural evolution and delineation of its likely synthetic route.”
In this report, the researcher and her colleagues state that “Despite its tremendous impact, the origin of SARS-CoV-2 remains mysterious and controversial. The natural origin theory, although widely accepted, lacks substantial support. However, the alternative theory that the virus may have originated in a research laboratory is strictly censored in peer-reviewed scientific journals. Nevertheless, SARS-CoV-2 exhibits biological characteristics that are inconsistent with a naturally occurring zoonotic virus. In this report, we describe the genomic, structural, medical, and literature evidence that, when considered together, strongly contradicts the natural origin theory. The evidence suggests that SARS-CoV-2 must be a laboratory-created product using the bat coronaviruses ZC45 and/or ZXC21 as a template and/or backbone.”
This report has been met with criticism that "there is no solid scientific evidence." Critics argue that most of the cited references are preprints ( not yet peer-reviewed) or similar sources, not scientific publications; and when scientific publications are cited, many are simply to express doubt about their findings. They contend that a preprint has not undergone the necessary review process before publication in a scientific journal, and therefore, while not invalidating the report's conclusions, they do consider it necessary to treat them with caution.
Given the various controversies, we are still faced with a puzzle that has not been fully assembled or is missing pieces. The most important thing now is to control and eliminate the virus, and in the meantime, to determine whether COVID-19 is truly a zoonotic disease or not.
Ramona Ávila Núñez, Ph.D.
References
- Lam, T.T.Y., Jia, N., Zhang, Y.W. et al. Identification of coronaviruses related to SARS-CoV-2 in Malayan pangolins . Nature (2020). 583, 282–285 https://doi.org/10.1038/s41586-020-2169-
- Yan, Li-Meng; Kang, Shu; Guan, Jie; Hu, Shanchang. Zenodo (2020) Unusual Features of the SARS-CoV-2 Genome Suggesting Sophisticated Laboratory Modification Rather Than Natural Evolution and Delineation of Its Probable Synthetic Route. https://zenodo.org/record/4028830
- NATIONAL GEOGRAPHIC. https://www.nationalgeographic.com.es/ciencia/como-pasan-coronavirus-animales-a-humanos_15392