Severe Acute Respiratory Syndrome (SARS) is caused by a coronavirus that is now believed to have originated in bats. In 2004, thousands of palm civets (a cat like carnivore) were killed off in China because it was believed that they were the main reservoir of this disease. Ooops.
It appears now that the civets had contracted the disease from humans, rather than the other way around.
Nearly a thousand people among the 8,000 or so infected died during that outbreak, and no human infections are known since early 2004.
A number of different researchers who have been looking at the source of SARS have suggested bats as the source, but this study apparently nails it down.
To arrive at these conclusions, Janies and colleagues secured genetic data of hundreds of different isolates of the SARS-CoV virus that had been found in humans, various bats, civets, raccoon badgers and pigs. Using the same equipment that was originally developed for the Human Genome Project, scientists determined the nucleotide sequence of each of the viruses. Bioinformatics came into play as the researchers linked many computers together to be able to analyze the massive amounts of data, comparing the viral genomes and building what is called a phylogenetic tree by searching for shared mutations. Phylogenetics is the study of the evolutionary relationships among various biological species, or in this case, viruses, believed to have a common ancestor.
The resulting tree is a branching diagram that illustrates the interrelationship of various viruses. The phylogenetic tree also shows the timeline of the travels and mutations of various strains of SARS as they jumped between host species. In this tree, the SARS-CoV virus traveled from bat hosts to humans, from humans to civets and pigs, and, in rare cases late in the outbreak, back to humans.
An extensive writeup is here. The work is to be published in the journal Cladistics.