After 3 years, the origin of the Covid virus remains unclear

The last scene of the film “Contagion” (2011) illustrates the path taken by the fictional virus that caused a pandemic in the cinematographic work. A bat carries a piece of banana, and the fruit falls into a kind of slaughterhouse. Then a pig puts it in its mouth.

Afterwards, already dead in a restaurant, the pig is prepared by a cook who, at a certain point, sticks his finger in the animal’s mouth. He doesn’t clean his hands well before greeting a customer played by actress Gwyneth Paltrow. This is where infection among humans begins.

The excerpt demonstrates the complexity involved in determining how the passage of a virus to a new species of living being occurs, as is the case with Sars-CoV-2 with humans. In general, the course occurs as shown in the film: the beginning of the transmission of a pathogen in which a microorganism that already exists in nature jumps between animals until it reaches humans.

In the case of the new coronavirus, an initial assumption was that a pangolin was an intermediary link that allowed the virus to move from other animals to humans. Despite the fact that the sale of the animal is illegal, it is common in Chinese markets – including in Wuhan, the city where the first cases of Covid-19 were registered, in late 2019.

Even though it was the most realistic hypothesis, doubts were raised, especially because of the Wuhan virology laboratory. One of the theories was that Sars-CoV-2 was being studied in this center and, from there, it had leaked.

This assumption was initially relegated to a conspiracy theory. However, it began to be considered as a real possibility. Journalistic investigations in heavy vehicles were made. Reports of pneumonia among lab workers days before the first official reports of Covid-19 stifled suspicion.

Another issue was about transparency: the Chinese did not share much information, and so the question arose whether the authorities in the Asian country were trying to hide something.

Another suspicion, this one even more conspiratorial, was that the Chinese were working to increase the degree of pathogenicity of Sars-CoV-2, a type of test called a gain-of-function experiment. In certain niches, it was even believed that the introduction of the virus into humans was on purpose.

In October 2021, the WHO (World Health Organization) organized a study in an attempt to put an end to this discussion. But that’s not what happened. The expedition report pointed out that, probably, a bat was the ancestral repository of the virus. Then, the pathogen infected a mammal traded at the Wuhan market.

The problem is that, due to the limited data, the team did not conclude how the pathogen spread among humans, leaving an open gap for the theory of laboratory leakage.

Even if the WHO’s gamble did not have the expected results, other studies already provide better information about the possible origin of the virus. By far the most widely accepted theory is that the pandemic started at the seafood market in Wuhan.

A study published in July in Science indicates that the first transmission epicenter of Sars-CoV-2 was in the market. If the virus had leaked from the lab, one would expect the initial transmissions to have come from there.

Fernando Spilki, a virologist and coordinator of the BR-MCTI Corona-omic Network, a laboratory project that sequences the genomes of samples of Sars-CoV-2 in Brazil, explains that the leak theory is not very plausible.

“First, because we have not seen transmission from [dos casos de pesquisadores do laboratório de Wuhan que apresentaram pneumonia]. Another thing is that she works with an accidental coincidence, “she says.

The theory of the gain-of-function experiment that was supposedly carried out by the Chinese is also refuted. This assumption was based on a property of the Sars-CoV-2 spike protein that increased the transmissibility and virulence of the pathogen.

The issue was that, until then, this property had not been documented in other types of coronaviruses. Therefore, the hypothesis was raised that the capacity could only have been checked through laboratory experiments.

However, more recent research has already observed this characteristic in viruses found in animals in the region of Laos, in Southeast Asia. “The molecular basis for the existence of a virus similar to Sars-CoV-2 is already beginning to be demonstrated in nature by the presence of similar viruses in bats”, explains Spilki.

For him, this new evidence is indicative that Sars-CoV-2 was formed in nature and, to infect humans, it must have undergone recombination with viruses closer to our species.

But something that still raises questions is the exact path from animal to animal so that, finally, Sars-CoV-2 reached humans. “We don’t know the whole web”, sums up the virologist.

Another open question is about patient zero. The virologist says that this point still has no definitive answer, and there is even a chance of simultaneous introductions of the infection in humans.

Even with these doubts, the theory of a natural origin of the virus already gives rise to the debate on how environmental degradation brings greater risk to public health emergencies. The film “Contagion” is an example for this. In the work, it is shown that a tractor knocks down a tree. Because of this, the bat, which is the probable reservoir of the virus in the work, flies off and begins the cycle of passage between species, until it infects humans.

For the virus that causes Covid-19, the kick may have been similar to what we saw on movie screens. “This kind of disorder [ambiental] seems to have been the beginning of the process that brings viruses, such as Sars-CoV-2, [para os humanos]”, Spilki concludes.