Scientists studying the genome of the virus causing severe acute respiratory syndrome (SARS) have found new evidence that the virus infecting humans originated in bats.
The outbreak of SARS from Asia to North America prompted a collaborative scientific and medical response to halt human infections and to share data about the virus's genetic characteristics. But scientists could not reach an agreement to identify the animal source of the coronavirus that caused SARS in humans, a virus known as SARS-CoV.
"Certainly, there are undiscovered viruses closely related to SARS and these viruses have novel associations with host animals that remain unknown," said Daniel Janies, lead author of the study
Prior studies had identified several species of Chinese bats as the natural viral reservoir in 2005, using a couple of genes from a few viruses.
Janies put those findings to the test with the comprehensive analysis of coronavirus origins, using whole genomes from hundreds of viruses.
Contrary to the notion that civets were the cause of SARS, the analysis revealed that the humans actually appear to be the source of the virus found in the civets.
Janies and colleagues designed an interactive map tracing the genetic, geographic and evolutionary history of SARS. The map also showed when and where the virus shifted from animal to human hosts.
They collected the genetic data of hundreds of different isolates of the SARS-CoV virus found in humans, various bats, civets, raccoon badgers and pigs and determined the nucleotide sequence of each of the viruses with the help of equipment originally developed for the Human Genome Project.
They compared the viral genomes and built a tree called a phylogenetic tree that illustrated the interrelationship of various viruses.
The tree showed 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 travelled from bat hosts to humans, from humans to civets and pigs, and, in rare cases late in the outbreak, back to humans.
SARS infected more than 8,000 and killed more than 900 people worldwide during a nine-month outbreak that ended in the summer of 2003, according to the World Health Organization.
"We don't fully understand SARS and whether or not it will come out of the wild again. SARS has opened our eyes to other kinds of viruses. Sequencing of more coronaviruses in exotic animals will teach us about their potential for disease," he said.
The research appears in the online early edition of the journal Cladistics.