Just as researchers feared, the virus behind the deadly severe acute respiratory syndrome (SARS) epidemic of 2003 is still out there: A Hong Kong group has found a relative of the human SARS coronavirus infecting a high proportion of the territory's Chinese horseshoe bats (Rhinolophus sinicus).
The original SARS outbreak, which killed more than 700 people around the world and sickened over 8000 in the winter of 2002-2003, was traced to weasel-like animals called masked palm civets being sold at live animal markets in southern China (ScienceNOW, 23 May 2003). Researchers suspected that civets were just a conduit and not the real reservoir for the SARS virus because it was not found in civets on farms or in the wild.
In searching for a reservoir, microbiologist Kwok-yung Yuen of the University of Hong Kong (HKU) and colleagues sampled monkeys, rodents, and several species of bats in the hinterlands of Hong Kong. The SARS-like virus was found in 39% of the anal swabs collected from Chinese horseshoe bats, which are both eaten and used in traditional Chinese medicine. In addition, around 80% of serum samples collected from the bats showed antibodies to the virus.
"This is the first time that a virus so close to the human SARS coronavirus has been found in wild animals," says Yuen, whose team reports its findings online this week in Proceedings of the National Academy of Sciences. "It shows that reservoirs of a SARS coronaviruslike virus exist in nature and provides evidence of the possibility of the re-emergence of SARS," he warns. Horseshoe bats are also widespread in mainland China.
Christian Drosten, a virologist at Bernhard-Nocht Institute of Tropical Medicine in Hamburg, Germany, who led one of the first teams to identify the SARS coronavirus in 2003, agrees. "It's quite convincing," he says, noting that two aspects of the situation are consistent with the bats being a natural reservoir for the virus: the high rate of infection among the bats and their reported lack of symptoms.
There is still a question as to just how closely related this bat SARS coronavirus is to the culprit behind the human outbreak, however. Yuen admits that despite similarities in proteins and genomic sequences, the viruses are distinct enough that they probably came from a common ancestor and were not transmitted directly from bats to civets. It also isn't clear if the bat coronavirus would have the deadly effect on humans that the human SARS virus has. "Even minor genetic changes can make a difference in the characteristics of a coronavirus," says Julie Hall, the World Health Organization (WHO) coordinator for communicable disease surveillance and response in Beijing.
University of Hong Kong Faculty of Medicine