hile the emerging severe acute respiratory syndrome virus has captured the attention of the media and public, one of the most deadly viruses known to man—Ebola hemorrhagic fever—has resurfaced, with a 140 cases of EHF, including 123 deaths, reported in the Republic of the Congo as of April 2003, according to the World Health Organization.
The disease, first identified in Africa in 1976, causes death in 50 percent to 90 percent of cases, according to the WHO. The virus is believed to have a natural reservoir, which has yet to be identified, in the rainforests of Africa and Asia.
"We've been looking for the source of the Ebola virus for years," said Jack Gelb, PhD, a professor and virologist at the University of Delaware, explaining that tracing the origin of a new or emergent virus requires a lot of digging and patience.
The hunt for origin of the SARS virus is also likely to be difficult and time consuming, according to several veterinarians and virologists following the outbreak.
Dr. Thomas G. Ksiazek, the chief of the Special Pathogens Branch in the Division of Viral and Rickettsial Diseases of the national Centers for Disease Control and Prevention, said that scientists examining the genome of SARS believe it is a new disease that has never before infected humans. But there is no definitive answer as to where it came from.
Several theories on the origin have SARS have been suggested. One theory that has received a lot of attention has been the possible transmission of the virus from domestic or wild animals to humans.
Conditions in rural China, namely inadequate sanitation and humans and animals living together, increase the possibility of a virus "jumping" from animals to humans.
"The conditions are right for that happening," said Dr. Gelb; however, he strongly cautioned that not enough is known about SARS to draw any conclusions.
Some researchers suspect SARS may have a reservoir in wild animals, because the SARS virus is so different from other known human and animal coronaviruses.
"We look for viruses in domestic animals and humans on a daily basis," said Dr. Jim Guy, an avian coronavirus expert at North Carolina State University. "We have a very good handle on the kind of viruses that are present in humans and domestic animals that exhibit clinical signs."
Less is known about viruses in wild populations. Dr. David Brian, a mammalian coronavirus expert at the University of Tennessee, said more research is needed on coronaviruses in wild populations in order to identify the origins of emerging viruses.
"We don't know the larger gene pool among coronaviruses," Dr. Brian said. "We need to isolate more coronaviruses from wild animals and sequence their genomes to know what we're dealing with."