Factbox: The origins of COVID-19

As a team from the World Health Organization works in China to investigate the origins of COVID-19, the following factbox looks at what we know about how the pandemic began.

CHINA ORIGINS
The coronavirus that causes COVID-19 - known as SARS-CoV-2 - was first identified in the central Chinese city of Wuhan in January 2020, and most scientists believe it is still most likely that it originated in China.

Peter Ben Embarek, WHO expert on food safety and zoonotic diseases, said Wuhan offered “the first solid clues” about the transmission of COVID-19 and any investigation would start there.

Though some studies have suggested COVID-19 was present in Italy or Spain earlier in 2019, and that it might have been responsible for a spike in pneumonia cases in France, few researchers believe it could have entered Wuhan from Europe.

Its closest relative in nature is the RaTG13 virus, which was discovered in horseshoe bats in southwest China’s Yunnan province. The 96.2% genetic match between the two makes it highly likely that COVID-19 also originated in the bat colonies of China’s southwest border regions.

HUANAN MARKET
The initial cluster of infections was traced back to the Huanan seafood market in Wuhan, leading many to assume that “patient zero” was probably a trader exposed to contaminated meat products.

But this version of events may be too simplistic to explain the patterns of infection in Wuhan and elsewhere.

Many of the earliest reported cases had no connection with the market. On Dec. 10, 2019, 41 Wuhan residents were hospitalised with what turned out to be COVID-19, but 13 of them had no link to Huanan.

A team of Chinese researchers said there were two types of SARS-CoV-2 circulating in Wuhan, only one of which was associated with the market.

Scientists also said the virus was unusually “pre-adapted” for rapid human transmission, making it unlikely that the first human contact was made at the seafood market.

INTERMEDIARY SPECIES?
WHO investigators are keen to find what the intermediary species was that allowed SARS-CoV-2 to move from its original bat host into humans.

Preliminary scientific papers in China identified snakes and mink as potential candidates, and similar coronavirus infections were also found in pangolins illegally trafficked into China.

But some scholars now believe there was no intermediary species at all, and that a SARS-CoV-2 like virus was transmitted directly from bats to humans, possibly on multiple occasions.

The first people infected were likely to be traders in bat meat, or in bat droppings used in traditional Chinese medicine, and one of them could have carried it into the Huanan seafood market, causing the superspreader event that allowed the pandemic to begin.