On the trail of the origin of Covid-19

While the Covid-19 virus (coronavirus SARS-CoV-2) continues to circulate and claim victims around the world, its origin is still unknown. Every scientific community promotes its hypothesis. Some suggest the possibility of an escape of the virus from a laboratory.

Another hypothesis, based on recent research related to the Chinese market in Wuhan and others conducted in Cambodia, Laos, Japan, China and Thailand, is an evolution from an ancestral virus found in bats, by the Horseshoe Bat family in especially in domestic or wild animals, then the passage of the virus from these animals to humans. During these various studies, several viruses with genetic sequences very close to SARS-CoV-2 were isolated in these bats.

A missing joint

Although it has now been proven that certain species of bats naturally harbor these coronaviruses, the identity of the domestic animal (s) or wildlife that would have acted as a relay between them and humans – lack of joints – is a mystery. Pangolin, who was originally a suspect, now appears more as a “security victim” than as one of those famous missing joints. One sequence of the coronavirus genome that was detected in Pangolins was actually related to the SARS-CoV-2 sequence, but the rest of the genome was genetically too far from it.

On the other hand, the pangolins on which viruses genetically close to SARS-CoV-2 had been isolated had most of the time been confiscated from live animal markets, at the end of the commercial chain, and had therefore been in prolonged contact. with other animal species. It is very likely that they have been polluted along this road and not in their natural environment. Mink farms have also been suspected in China.
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Finally, pangolins and horseshoe bats do not share the same habitats, making possible contact between the two species very unlikely where the virus would have passed from a bat to a pangolin. Civettes and / or raccoon dogs may form an intermediate reservoir for SARS-CoV-1). Rodents or primates can also carry pathogens with zoonotic potential, such as Hantavirus, which can cause hemorrhagic fever with severe kidney syndrome or Filovirus, including Ebola virus, in particular. The latter are transmitted to humans by wild animals, especially fruit bats, hedgehogs and primates such as chimpanzees or gorillas, and then spread in the human population mainly through direct contact with blood, secretions and other body fluids from infected humans. The average death rate is around 50%.

In 2013, the first cases of Ebola virus disease (EVD) were discovered in West Africa. This occurrence will cause more than 10,000 deaths mainly in Guinea, Liberia and Sierra Leone.

Bushmeat consumption: a risky practice

The risk of transmission from animals to humans, a phenomenon known as spillover, whether during hunting, handling animals or consuming wild meat is therefore real and potentially devastating.

It is the characterization and quantification of this risk in Cambodia that the ZooCov project has been exploring through a “One Health” approach, for almost 2 years and since the start of the pandemic, if so, and how pathogens such as coronavirus could be transmitted from wild animals , hunted and eaten, to humans.

In Southeast Asia, wildlife trade and bushmeat consumption is a common practice. Often opportunistically, this consumption comes in certain communities to supplement a low protein diet. It can also be regular and targeted. In Cambodia, 77% of 107 families interviewed during ZooCov said they had eaten bushmeat in the previous month.

Medical use is also widespread. In Vietnam, the analysis of reports of confiscations of pangolins and derivatives carried out between 2016 and 2020 by the Vietnamese authorities shows 1,342 live pangolins (6,330 kg), 759 dead pangolins or carcasses (3,305 kg) and 43,902 kg of dandruff.

But this consumption also has a cultural and social aspect which is still poorly understood. For affluent classes, and often in large cities, this consumption may be motivated by a need for social recognition, beliefs that the consumer of this meat acquires the physical or physiological virtues of the animal consumed, or by a desire to challenge the consumption of industrial consumption. meat that is harmful to health. Wildlife farming to meet this demand and / or fur production is also widespread.

In Cambodia, in the provinces of Stung Treng and Mondolkiri, where forested areas still exist, more than 900 people living on the edge of these forests were interviewed in an attempt to analyze the structures and function of commercial, illegal bush meat. . Statistical analyzes are underway to identify the people most at risk of coming into contact with such pathogens. We already know that the vulnerable are mainly young middle-class men. Some societies are also more vulnerable than others. Sociological studies have also made it possible to better understand the current context – the legal framework, the profiles of the actors in this trade, their obstacles and their motives, linked to the trade in wild animals and their consumption, and the development of this context across the various health crises (bird flu, Ebola, SARS-CoV-1, etc.).

Which populations may be at risk?

These successive crises seem to have little bearing on the practices of these societies. In addition to regular consumption, a quarter of the families interviewed still reported hunting or trapping, and 11% said they sold bushmeat and / or wildlife. In addition, and at the same research sites, more than 2000 samples of wild animals that are the subject of human trafficking or subsistence consumption – bats, rodents, turtles, monkeys, birds, wild boars, etc. have been analyzed. Some of the samples tested positive for coronavirus in particular and are being analyzed at the Institut Pasteur du Cambodge (IPC) to sequence the genome and learn more about its origin, evolution and zoonotic potential. Finally, blood samples were taken from more than 900 people who were examined in the same area to find out if they had been in contact with one or more coronaviruses. The analyzes are still ongoing, but we already know that at the time of the investigation, these individuals had not been exposed to SARS-CoV-2.

The Covid crisis has clearly shown this: it is important to detect these occurrences early in order to take action as soon as possible to prevent the spread of pathogens. And if there are still many questions about the mechanisms of emergence, the same logically applies to the monitoring systems that need to be established to monitor them. The results of the ZooCov project will be used to develop a system for the early detection of contagious events of zoonotic viruses, in particular by strengthening the wildlife health monitoring system already in place in Cambodia and set up by Wildlife Conservation. Society WCS. Other important research and development projects will contribute to the understanding of these emerging phenomena, to their prevention and to their early detection.

The authors thank Cambodia’s Ministries of Health, Agriculture, Livestock and the Environment as well as all project partners: Institut Pasteur du Cambodge (IPC), Wildlife Conservation Society (WCS) Flora and Fauna International (FFI), Research Institute for Development (IRD), Hong Kong University (HKU) , GREASE Network, International Development Enterprise (iDE), World Wildlife Fund (WWF), Elephant Livelihood Initiative Environment (ELIE), BirdLife International, Jahoo, World Hope International.

The original version of this article was published on The Conversation on May 2, 2022.

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