Civets got Sars from humans: US study
Stephen Chen in Beijing
Virus claim disputes the popular theory
A US study on the evolution of Sars has challenged a popular hypothesis established by Hong Kong and mainland scientists that the deadly virus was passed to humans by civet cats.
The severe acute respiratory syndrome corona-like virus found by researchers in palm civets kept in restaurant cages in Guangdong was actually passed from humans to the animals, not the other way around, an Ohio State University research team said.
But leading scientists in Hong Kong and the mainland said there was no new evidence to back up the team's contention.
The theory, posted online in the early edition of the research journal Cladistics, says only a small number of people who were in daily contact with civets were infected because the animal was not an amplifying source of the virus but an inheritor.
It has been half a decade since the global outbreak of the epidemic, but the original carrier of the virus - although almost certainly a mammal - had not yet been identified, the researchers said.
If the theory is accurate, the culling of nearly 10,000 civet cats by Guangdong authorities in 2004 may have been in vain and the widespread belief that Sars was eradicated that year because of the campaign against the animals could be dangerously wrong.
Daniel Janies, lead author of the study and an assistant professor of biomedical informatics at Ohio State University, said his team's findings backed up a 2005 Hong Kong study by Yuen Kwok-yung, director of the University of Hong Kong's department of microbiology, that the origin of the Sars virus could be traced back to bats.
But their opinions diverge on how the virus jumped to humans.
'With the data at hand, we see how the virus used different hosts, moving from bat to human to civet, in that order. So the civets actually got Sars from humans,' Professor Janies said. 'We see this evolutionary sequence of events, but other biochemical reports of the poor interaction of bat viruses and human cells suggests there remains a missing link in the wild.'
Professor Yuen disagreed, saying the virus originated in bats and passed to an unknown host before being transmitted to civets and then to humans.
'The ancestor of the Sars coronavirus was in bats. The bat virus jumped to another mammal and mutated towards a human Sars-like virus. The mutated bat virus went from this unknown mammal into the civets. The virus mutated into a form as the civet Sars coronavirus, which is 99.8 per cent similar to the human virus,' he said.
'The virus then jumped from the civet and spread between humans as the human Sars virus.'
But the scientists did agree that there was a mysterious mammal responsible for the evolution of Sars from an animal to a human virus, the most important link in the epidemic's evolution.
A spokeswoman for the Shenzhen Centre for Disease Control and Prevention said the latest research was not conclusive, 'so we cannot say whether killing civets was wrong'.