The genetic sequence of the new virus in Wuhan, China, quickly led virologists to conclude it had a bat origin. Animal coronaviruses infect people quite frequently. After sampling a cave in Southern China for five years, scientists reported a coronavirus menagerie in its bat residents, including 11 similar to the SARS virus (PLOS Pathogens, doi:10.1371/journal.ppat.1006698).
Blood samples from villagers living near this cave revealed 3% had antibodies to bat coronaviruses (Virologica Sinica, doi: 10.1007/s12250- 018-0012-7). ‘If you extrapolate the percentage to where the bats live, across southeast Asia, you are talking about one to 7m people a year getting infected and exposed to bat coronaviruses,’ says disease ecologist Peter Daszak, President of EcoHealth Alliance in New York involved in both surveys.
More than half of the first 48 Covid-19 patients were associated with a seafood market in Wuhan.
When investigators from the Chinese Center for Disease Control visited the market, they found traces of the virus on environmental swabs, but not in animals. ‘By the time they sampled the market, I think not every wildlife species traded there was present. That is why they missed the chance to sample the animals,’ says virologist Lin-Fa Wang at the Duke Global Health Institute, Singapore.
Reports linking the virus to an escaped lab virus and snakes have been effectively dismissed. Viruses similar to SARS-CoV-2 were reported from Malayan pangolin (Nature, doi: 10.1038/ s41586- 020-2169-0).
But virus RaTH13 isolated from a horseshoe bat in southern China is 96% identical to SARS-CoV-2 (Covid-19 virus), the nearest relative to the pandemic virus found thus far.
SARS virus and SARS-CoV-2 are capable of infecting human cells through the enzyme ACE2 (Nature; doi: 10.1038/s41586-020- 2179-y).
The pandemic virus binds more efficiently to it. However, the RaTH13 bat virus can also bind to the human ACE2 receptor. According to the researchers, there might not be a need for an intermediate species for Covid-19 – the virus may have come directly from a bat.
Daszak says small family farms in China have begun to mix all sorts of species, such as chickens, goats, civets, ducks, porcupines. If bats infect these animals, they could then be a source of infection in people. ‘It [also] is plausible that people are picking up these viruses directly from bats, as just part of their everyday life in China and Southeast Asia, and there have been other outbreaks or people died and it was not noticed,’ says Daszak.