Blame bats for SARS, U.S. researchers say

Civet cats got a bad rap as the animals that spread SARS to humans, U.S. researchers said Tuesday.

Chinese scientists fingered the civet cat as the SARS agent, but bats are the most likely reason that severe acute respiratory syndrome (SARS) spread to people, Ohio State University scientists said.

SARS killed 900 people in 2003, including 44 in Canada.

Based on studies of the genome of the virus that caused SARS, "the real story is that civets were not the animal reservoir of SARS," Ohio State  biomedical informatics professor Daniel Janies said in a release.

In fact, "the civets actually got SARS from humans," he said.

The researchers found that bats harboured a SARS strain that is the best example of the virus before it infected humans, although there are still problems with the theory because there are missing links in the chain between animals and people.

The bat virus doesn’t interact well with human cells, so there must be other animals that served as intermediate hosts.

If civets were not the transmitters, then the Chinese purge of the animals in 2004 is not likely to eliminate the risk of new outbreaks, the researchers said.

"Certainly, there are undiscovered viruses closely related to SARS and these viruses have novel associations with host animals that remain unknown. Our lack of knowledge of viral and host diversity around the world is a source of concern for the re-emergence of a SARS-like disease," Janies said.

Hundreds of samples studied

The U.S. researchers were not the first to suggest bats were the source of SARS, but said they had done the largest and most comprehensive analysis of the origin of coronavirus, which causes SARS.

The researchers studied genetic data from hundreds of virus samples taken from humans, various bats, civets, raccoon badgers and pigs. Then, using the same equipment developed for the Human Genome Project, they analyzed each virus.

Computers were used to create a "phylogenetic tree" which identifies common ancestors shared by viruses (or other species) by searching for shared mutations.

The researchers found that the SARS virus travelled from bats to humans to civets and pigs, and, late in the outbreak, back to humans.

Janies and his colleagues also studied viruses outside the SARS group to rule out other possible coronavirus sources.

"You need to search outside of the viruses involved in the outbreak to create a baseline so you have a point of reference and then from that root of the tree, you can read the entire history of the exchange of the virus among hosts," Janies said.

Farhat Habib, Boyan Alexandrov and Diego Pol from Ohio State and Andrew Hill of the University of Colorado worked on the study, published in the online edition of the journal Cladistics.

Civets are a wild animal considered a delicacy in southern China.