Corona pandemic: search for the origin of the virus

The corona virus continues to spread rapidly around the globe. But where does it come from? Scientists around the world are trying to trace the pathogen’s traces. But the place of origin is still uncertain.

By Christian Baars and Stella Peters, NDR

Michel Schmitt sits in front of his computer and points to white spots in the image of a lung. They are typical signs of a Covid 19 disease. The amazing thing is: This picture was taken on November 16, 2019 last year.

Schmitt is a radiologist at the Albert Schweitzer Hospital in Colmar in Alsace, not far from Freiburg. The region in France was particularly badly affected by the corona pandemic in spring. Back then, Schmitt analyzed hundreds of lung images from patients. “With the experiences of March and April, I came up with the idea of ​​going through all the pictures from summer 2019 and looking for atypical signs,” says the radiologist. In fact, he found it.

On the recordings from November 16 and twelve others from December, he discovered evidence of Covid 19 disease. At that time they would have considered the patients to be “strange cases of flu”, “with fever, pulmonary embolism, pneumonia,” says Schmitt. But that “all did not fit together”.

First corona cases in France in November?

Could it be that some people in France had Corona as early as mid-November? Schmitt had the patients examined for antibodies retrospectively. The results were positive. However, he cannot rule out that they may have been infected in the meantime.

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But there are other studies that suggest the virus had already spread for a few weeks or even months before it was discovered in Wuhan in late December. For example, researchers in Italy and Brazil found traces of the pathogen in stored wastewater samples that were taken in December and November, respectively. And in China itself – the newspaper “South China Morning Post” reported a few months ago – there was apparently a first proven infection as early as mid-November.

Understand the virus’s hiking trails

So since when has the virus actually been spreading among people? And where does it come from? Scientists are trying to trace the path of the virus using various methods. Peter Forster also took part. The geneticist works in Cambridge and usually deals with changes in the human genome to find out when and where early ancestors spread on the planet. “I have spent 20 years tracing human migrations over the past 200,000 years,” says Forster. These methods would also be ideal for tracing “the virus’ path”.

Together with colleagues, including his brother in Kiel, he analyzed the outbreak of the SARS-CoV-2 coronavirus. They came to the conclusion that the pandemic most likely started between mid-September and early December – and quite certainly in China or a neighboring country. Schmitt does not surprise him that the virus was already sporadically in Europe a short time later: Documented, later cases showed how quickly travelers could bring the pathogen to other regions, he says.

Bat pathogens are genetically similar to SARS-CoV-2

Most other scientists also believe that the outbreak began in Asia in the second half of 2019. When, where and how exactly the first person was infected is still unclear. “There are many indications that the pathogen originated in a bat reservoir in southern China,” says Thomas Mettenleiter, head of the Friedrich Löffler Institute (FLI), the Federal Research Institute for Animal Health. Pathogens that are genetically similar to the new SARS-CoV-2 virus have been found in certain bats in southern China, says Mettenleiter. That is an indication, but not yet proof of the origin.

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According to a study by an international team of scientists published in the journal “Nature” at the end of July, viruses that are closely related to SARS-CoV-2 have been circulating in horseshoe bats for many decades. And these pathogens have properties that enable them to infect human cells. This means that whenever there is contact between the animals and humans, the viruses can jump over and possibly change in such a way that they can spread widely among humans.

However, the researchers cannot say when and where this actually happened during the current outbreak. They indicate that the horseshoe bat bat is widespread in different regions of China and in neighboring countries.

Difficult to get suitable samples

Even for the World Health Organization (WHO), questions about the origin have not yet been clarified. A team of scientists should therefore carry out further investigations on site. Two experts, a veterinarian and an epidemiologist, were in China in July. You should prepare a larger study of the possible source of the infection. WHO chief Tedros Ghebreyesus said in early August that this mission should begin shortly. When exactly is still unclear – and also whether it will be successful.

In any case, Thomas Mettenleiter from the FLI is skeptical whether it can ever be reliably proven when and from which species the virus came to humans. The search for clues is particularly difficult at the moment, “because we have a humane pandemic,” says Mettenleiter.

The pathogen is “now spread practically everywhere”. And that means: Even if it is possible to detect the viruses in nature, it must first be clarified “whether they are not reintroductions from infected people,” says Mettenleiter. It would therefore be best to examine samples that were taken before the outbreak of the pandemic. It is uncertain whether the scientists will find what they are looking for.

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