Coronavirus: Bats likely the source, but other animals may have helped transfer disease to humans, says study
Figuring out the animal source could help health experts contain the infection that has sickened over 7,711 people and killed over 170 in China
As scientists try to hunt down the animal source of the Wuhan coronavirus infections, a group of scientists believes that the deadly virus may have hopped on to humans from bats.
But another mysterious animal may have been involved as an intermediary, transferring the virus from bats to humans, say scientists who have published their findings in Lancet.
The Wuhan coronavirus also called 2019-nCoV is a zoonotic virus, meaning some animal has transferred the virus to humans. Figuring out the animal source could help health experts contain the infection that has sickened over 7,711 people and killed over 170 in China.
Earlier, China said that the virus may have emerged from Wuhan's Huanan Seafood Wholesale Market where a variety of animals, including civet cats, snakes, dogs, peacocks, otters, camels, and koalas were being sold. With the seafood market as the narrowed target, scientists began looking for animals that may have been the culprit.
But so far, studies have provided conflicting reports, some believing that snakes were the source, while others were more inclined toward mammals like bats.
Just last week, a Lancet study pointed out that a third of the initial infections occurred in people who had no exposure to the seafood market, which led a few scientists to suspect that the virus may not have its origins from the Huanan market.
According to the current findings, the virus is most closely related to two SARS-like coronaviruses whose origins can be traced to bats — these mammals are thought to be the natural host of Ebola virus, rabies, SARS, and MERS.
"These data are consistent with a bat reservoir for coronaviruses in general and 2019-nCoV in particular. However, despite the importance of bats, it seems likely that another animal host is acting as an intermediate host between bats and humans," says Professor Guizhen Wu, Chinese Center for Disease Control and Prevention and one of the authors of the study.
In this study, Wu and her colleagues extracted virus samples from nine patients in Wuhan and scanned the genome to read their sequence. Of the nine patients, eight of them had visited the seafood market, before they fell sick. And one patient had never visited the market but had stayed in a hotel near it.
The results show that the viral samples collected from these patients were strikingly similar — their genome sequences were 99.98% identical. This, according to the authors, indicates that the virus has taken to humans very recently. As time progresses, the virus will evolve, showing variations in its genome, say experts.
"It is striking that the sequences of 2019-nCoV described here from different patients were almost identical. This finding suggests that 2019-nCoV originated from one source within a very short period and was detected relatively rapidly. However, as the virus transmits to more individuals, constant surveillance of mutations arising is needed," says one of the lead authors Professor Weifeng Shi, Key Laboratory of Etiology and Epidemiology of Emerging Infectious Diseases in Universities of Shandong, Shandong First Medical University and Shandong Academy of Medical Sciences, China.
And when the team compared the genome of the Wuhan coronavirus with other viruses, they found that it was closely related to SARS-like coronaviruses of bat origin, sharing 88% of its similarity.
The data suggests that an intermediate animal source was at play because the infection arose when most bat species in Wuhan were hibernating, explains Wu. Further, no bats were sold or found at the Huanan seafood market at that time and many non-aquatic animals (including mammals) were being sold. And as the Wuhan coronavirus and the bat-derived coronaviruses were only 90% identical, the new virus may not have been a direct ancestor of these closely related viruses, she adds.
"In both SARS and MERS, bats acted as the natural reservoir, with another animal acting as an intermediate host, and with humans as terminal hosts. This again highlights the hidden virus reservoir in wild animals and their potential to spill over into human populations," she says.