A World Health Organization report on the origins of COVID-19 has come as a disappointment to those who were expecting a conclusion on the source of the virus that has killed 2.8 million people worldwide.
After spending two weeks in Wuhan with Chinese scientists in February, WHO experts said in the 120-page document, released Tuesday, that it is “very likely” that the virus spread via an intermediate animal host to humans, but did not completely rule out other hypotheses, including the possibility that the virus was transmitted through frozen food products or came from a lab leak.
The WHO chief, Tedros Adhanom Ghebreyesus, called for more studies and data sharing, while several governments, including Washington, expressed concerns on the delayed study and a lack of transparency, including China’s denial of access to some original data and samples.
But scientists say the WHO trip was only the beginning. Tracing the source of a new virus often takes years and the collective efforts of researchers around the world. In some cases, viruses’ exact origins remain a mystery decades after they first emerge.
“Origin investigations are like searching for a needle among countless haystacks that also contain a lot of other needles,” Angela Rasmussen, a virologist at Georgetown University, told VICE World News. She said collaboration and diplomacy will be required as scientists carry on research about SARS-CoV-2.
“This is a long and quite possibly fruitless effort, yet it is an essential one, both to understand this pandemic and to better strategize how to prevent the next one.”
Here is how long it takes for scientists to trace some of the viruses that caused deadly epidemics in the past.
SARS-CoV: five years and more
The SARS epidemic first occurred in the southern Chinese province of Guangdong in November 2002. In March 2003, three teams of scientists in Hong Kong, the U.S. and Germany identified and isolated the SARS-CoV virus.
In May that year, Chinese scientists identified the virus in masked palm civets and other animals in Guangdong. And in the following months, some patients were found to have contacted civets at a restaurant. This was cited as evidence that the animal was an intermediate host of the virus.
In 2005, scientists from Hong Kong identified several SARS-CoV-like viruses in China’s horseshoe bats. In 2017, five years after the outbreak started, scientists from the Wuhan Institute of Virology traced the virus to bats living in a cave in the southwestern province of Yunnan, after sampling thousands of horseshoe bats in locations across the country.
But some scientists say more evidence is needed to demonstrate how the virus could have jumped from bats to civets.
Ebola virus: four decades and more
The first outbreak of Ebola virus disease was reported in the Democratic Republic of Congo in 1976. However, scientists still do not know where the virus came from, despite extensive investigations, according to the U.S. Center of Disease Control and Prevention.
The virus is transmitted to people from infected animals, such as fruit bats, chimpanzees, gorillas, monkeys, forest antelope or porcupines, and further spreads through human-to-human transmission.
While scientists believe bats are the most likely source of Ebola, they still don’t have enough evidence to draw a conclusion.
MERS-CoV: years and more
Middle East respiratory syndrome, caused by a novel coronavirus MERS‐CoV, was first identified in Saudi Arabia in September 2012.
In 2013, scientists found that bats carried viruses that were genetically closely related to MERS-CoV, although they could not find direct contacts between bats and humans in places with MERS outbreaks.
The same year, MERS-CoV antibodies were found in dromedary camels, as researchers screened animals including camels, cattle, sheep, and goats. More research conducted in 2013 and 2014 found camels were carrying nearly identical MERS-CoVs as humans, suggesting camels could have passed the disease to humans.
However, the exact transmission routes between bats and camels remain unclear. Some research suggests other animals such as alpacas could also serve as a reservoir for the virus. Retrospective studies also discovered earlier cases of MERS in neighboring Jordan, in April 2012, according to the U.S. CDC.
HIV: four decades and more
Acquired Immune Deficiency Syndrome (AIDS) was first recognized as a new disease in the U.S. in 1981. The HIV-1 virus (one of the two viruses that cause AIDS) was first isolated and identified in 1983 at the Pasteur Institute in France.
In the next few years, researchers found the so-called simian immunodeficiency virus (SIV) from captive rhesus macaques, which caused similar symptoms as AIDS in humans. Other researchers in America later found in wild chimpanzees a type of SIV similar to HIV-1. HIV-2, a rarer type of HIV, was similar to a virus found in sooty mangabeys, a monkey in West Africa.
In 1998, scientists in America managed to found the earliest known HIV infected person—a man living in the then-Belgian Congo in 1959. The HIV he carried appeared to be an ancestor of several subtypes of HIV that later spread across the world.
Scientists say these viruses might have hopped from monkeys and chimpanzees to humans during the butchery of bushmeat, but the details remain unknown.
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