The virus that causes covid – 19, SARS-CoV-2 has already infected more than million people and caused the death of more than 2.8 million .
But more than a year after the first cases reported in the Chinese city of Wuhan, the origin of the virus remains an enigma.
The report released this Tuesday by the World Health Organization (WHO) does not offer answers either , after the visit to China by an international team of researchers.
The experts arrived in Wuhan in search of the origin of the virus, but they had to be content with samples and evidence provided by the Chinese authorities. WHO Director Tedros Adhanom Ghebreyesus urged China to share data “more extensively” in the future.
Given these difficulties, what then is known about the origin of SARS -CoV-2? At the moment “ all the hypotheses are on the table “, affirmed Dr. Tedros.
According to the WHO report it is most likely that the virus has passed from bats to humans through some kind of intermediate animal .
And it qualifies the hypothesis that the virus has escaped from a laboratory in Wuhan, something that China rejects, as “highly unlikely”, although it does not rule it out entirely. Tedros stated that the hypothesis “requires further investigation potentially in other expert missions.”
However, even with additional missions and greater data transparency from China, solving the mystery of the origin of SARS-CoV-2 will not be easy.
“ Finding the origin of a virus when it comes to solving where a disease started is notoriously difficult ,” said Dr. David Nabarro, special envoy on covid- 19 of the WHO, in statements to the BBC’s Today radio program.
“We do not know precisely the origins of HIV, nor of Ebola, and it will take a long time to find the precise origins of covid – 19 ”.
Nabarro stated that“ WHO should not be judged by the results achieved so far in regarding the origin of the virus “, because trying to determine those origins” always takes much longer than people think. “
“Origin” of a virus
When we talk about the origin of a virus, “there are two origins that must be clearly distinguished,” Fernando González told BBC Mundo Candelas, specialist in molecular epidemiology of viruses and bacteria, professor of genetics at the University of Valencia and researcher at FISABIO, Foundation for the Promotion of Health and Biomedical Research of the Valencian Community.
“ An origin is which is the animal reservoir in which the virus is found in the wild state not associated with humans.”
“ And another is the origin of an epidemic or pandemic in which we have to find the origin of the transmission of the virus in human os. ”
In some cases the natural reservoir may be known, for example, certain species of bats, but the origin of the epidemic may never be determined, that is, which species acted as intermediaries between the natural reservoir and humans.
The cases of SARS and MERS
The epidemics of SARS (severe acute respiratory syndrome) and MERS (Middle East respiratory syndrome) were caused by coronavirus, as is the current covid pandemic.
More than 8. 000 people got sick with SARS in 2003, of which about 800 died. MERS disease affected 2012 to about 1. 000 people and caused close to 400 deaths. Both epidemics spread to more than twenty countries.
Both in the case of SARS and MERS it was possible to determine not only the natural reservoir but also the intermediate species.
However, These are “two exceptional cases” , stated González Candelas.
“In the case of SARS, the natural host was identified in bat species, and the origin of the human epidemic in civets , a small mammal. ”
In other words, a virus close enough to SARS virus in humans to determine that these mammals were indeed the intermediate species.
“In the case of MERS, the intermediate hosts were dromedaries “.
The researcher pointed out that” there are people who think that in the same way Once the SARS and MERS intermediary has been found, the SARS-CoV-2 intermediary has to be found. ”
But he warned that there is a difference“ which in this case is crucial. ”
The difference with SARS-CoV-2
SARS and MERS cases were quickly and easily identified because affected individuals were showing symptoms shortly after infection.
“So it is much easier to keep track of where you have been infected, with whom you have been and what you have been in contact with.”
“The SARS-CoV-2, on the other hand, can be transmitted from people who do not show symptoms, it can be transmitted silently, hidden from health systems years for a time that we don’t know how long it is, possibly weeks, or one or two months, ”explained González Candelas.
The head of the WHO international mission that traveled to China, Peter Ben Embarek pointed out that is “perfectly possible” that there were already cases circulating in Wuhan in October or November of 2019 .
China reported the disease to WHO on January 3, 2020, one month after the first reported detection.
“The first reliably reported case is from the beginning of December, and there is not one at erta epidemiological that draws minimal attention until the end of December “, pointed out González Candelas.
” What was there a month before that could have caused the original infection? We do not know, because we do not even know if this occurred in Wuhan or in another locality “.
” We already know that the origin of the virus It is not in the Wuhan market. That is an epidemic starting point, but the virus was already circulating before ”and the jump to humans could have occurred elsewhere.
The hypotheses
¿ What is known then about the origin of SARS-CoV-2?
“ We have identified the evolutionary origin (the natural reservoir) in several species of bats “, Stated González Candelas.
” Work is being done very intensively on it and there are very recent articles that report the detection of coronaviruses very close to SARS-CoV-2 in species of bats in Southeast Asia, both in China and in other countries. ”
“ What no one has found yet is the intermediary , which is what the WHO team was going to look for as a working hypothesis. ”
The Spanish researcher I am sure that two hypotheses have been raised “with a certain scientific basis.”
“One is that there is one or more species of other animals that have acted as intermediaries and we have not identified them”.
“Another possibility is that the virus has escaped from an experimental laboratory, for which no evidence has been found. It is very difficult to show that something has not been produced in the way someone suggests, since there is always someone who can say ‘I am convinced that the virus has originated in a laboratory’. As scientists we can say, you are the one making the claim, where is the evidence to support it? And there is no proof. ”
“ The WHO team concluded that the hypothesis is very unlikely because with the information available there is no data to support it, but cannot say that it has not occurred . That is why they are cautious. ”
Regarding the hypothesis that the virus jumped to humans through species intermediaries, finding them will not be easy.
The Chinese authorities quickly eliminated “all biological remains from the market, which were closed and dismantled” , stated González Candelas.
“This is a posteriori criticism when we want to find the origin, but at the moment when the public health authorities have to stop an epidemic outbreak, that’s what we have to do to prevent the spread of a pandemic. ”
Ebola and HIV
Dr. Nabarro cited both diseases as examples of unidentified origins.
In both cases l or what is known is what the natural hosts are, explained González Candelas.
“In the case of HIV, there are several species of primates. But HIV has not entered the human species only once, it has possibly entered tens or hundreds of times “.
HIV, which continues to be one of the biggest problems for global public health, it has already been charged almost 33 millions of lives, according to WHO.
“The HIV pandemic today is the result of six, seven independent introductions, all of them produced in the same area of central Africa from different species of chimpanzee or mangabey, which is another primate, independently. ”
“ This means that the virus of simian immunodeficiency occasionally comes into contact with the human species, with some variant that allows its transmission between us. But we cannot say what the origin has been. ”
“ The origin of these transmissions that give rise to the pandemic possibly date back to the years 20 the last century. We cannot find the entire chain of transmission, and we cannot say what the intermediary has been, if any. ”
In the case of HIV, it is known, according to the researcher, that there are food preparation practices in which the blood fluid of people who cut meat with machetes and knives, “in situations of no hygiene and precaution”, come into contact with wildlife, chimpanzees and other primates that are consumed as food.
“For us it can be repulsive and very little edifying but for them it has been a traditional means of obtaining a food rich in protein.”
The researcher points out that these repeated jumps of the immunodeficiency virus from primates to humans did not have in the vast majority of cases epidemic significance .
“Perhaps because few people were infected, but neither the communications nor the transmission capacity of a virus such as HIV were as great as they are now for the coronavirus, apart from the fact that the mechanism is very different. ”
In the case of Ebola, scientists found very similar viruses in bat species.
“But what is the one that caused each of the Ebola outbreaks that have been seen for forty or fifty years? , because we do not know “.
“In most cases it is impossible to know, because when we want to find out is when an infection has already occurred that draws epidemiological attention or cl Unique to our species. ”
“ Variants of the Ebola virus are distinguished, each of which, although they are known as geographically separated, will also possibly be s biologically separated . And we cannot know which of them has been responsible for an outbreak, but in the case of Ebola there has not been an interest or means to find out. ”
Unlike the SARS-CoV- 2, Ebola manifests symptoms very quickly and if an outbreak is detected it is easier to find out who has been the patient zero of the outbreak and where they have been and what they have been in contact with.
“Research there would have a greater chance of being successful , but it is not carried out because there are no means to do it “.
The Ebola epidemic of 2014 – 2016 in West Africa caused the deaths of more than 11. 000 persons.
“It would be very surprising”
Elucidate the origin of a virus will not influence how you treat it.
But it is important because it allows to prevent future cases of species jumping , explained González Candelas.
“Determining the origin of the virus allows us to direct our surveillance for the prevention of future epidemics to high-risk species or geographical areas, since if we do not identify the origin, we will be blind and wasting resources because they will not be used efficiently ”.
For the Spanish researcher “the most plausible thing in the case of SARS-CoV-2 is that there has been a series of intermediate species but not the entire species, but individuals intermediaries “.
It is enough then that a few animals on a farm or farms, or in a market, function as intermediaries.
“We do not know what the chain of transmission, and without knowing it, we may be looking at one of the representatives of that intermediary species who has not been involved in the transmission. If it is virus-free, we are going to say ‘there is no virus’ in the civet or in a badger or in any other species, but we are looking at what there is today “.
“We cannot be looking for what was three years, ten years, or forty years ago, which is the distance that is supposed to separate viruses in bats from viruses that have already appeared in humans ”.
González Candelas assures that it will be very difficult to determine which was the intermediate species in the case of SARS-CoV-2.
“Most likely we will not be able to find the origin of the virus. In my view, it is very, very difficult, and it would be very surprising if it happened because we have many unknowns that will be very difficult to solve ”.
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