Only 34 days after the mysterious disease known as SARS was first identified, Dutch researchers have produced the disease in monkeys by infecting them with a recently discovered coronavirus, producing the final piece of evidence that the virus is the cause of the outbreak.
“We now know with certainty what causes SARS,” said Dr. David L. Heymann, executive director of the World Health Organization’s Communicable Diseases programs. “With the establishment of the causative agent, we are one step closer” to developing more effective preventive programs and treatments, he said.
The announcement came Wednesday as severe acute respiratory syndrome continued its spread through Asia. There were 58 new cases of SARS reported by WHO Wednesday -- 50 of them in mainland China and Hong Kong, the epicenters. The total number of cases stands at 3,293 with 159 deaths.
The U.S. Centers for Disease Control and Prevention reported 199 probable and suspected cases of SARS in the United States, but experts said the number could drop as to as low as 30 by the end of the week as new diagnostic tests weed out suspected cases that are actually other illnesses.
U.S. Health and Human Services Secretary Tommy G. Thompson warned Wednesday that China has been underreporting the number of cases there and said that U.S. physicians are very concerned about the rapid spread of the disease in the region.
“I’ve got to tell you, my doctors, I’ve never seen them quite as concerned about anything as they have been about SARS,” he said while on an official visit to Italy. “It’s new, and they are really concerned about it turning into an epidemic.”
Although most experts have been convinced that SARS is caused by the new coronavirus -- whose genetic blueprint was identified Sunday by a Canadian laboratory and Monday by the CDC -- actual proof requires fulfilling four conditions known as Koch’s postulates. To identify a virus as the source of a disease, scientists must show that it is present in all cases of the disease; that it can be isolated from the host and grown in the laboratory; that it can produce symptoms of the original disease when introduced into a susceptible animal host; and that it can be isolated again from that animal.
A team led by Dr. Albert Osterhaus of the Erasmus Medical Center in Rotterdam, the Netherlands, said Monday they had fulfilled the last two postulates. They placed the virus in the noses of monkeys and found that the animals developed symptoms similar to those exhibited by humans with SARS. Lung tissues from the monkeys showed damage similar to that found in humans as well.
They then were able to isolate the virus from the monkeys and grow it in laboratory dishes, fulfilling all of Koch’s postulates.
In addition to providing the final proof of the virus’ role, the experiments also represent a crucial step toward the ultimate development of a SARS vaccine. Licensing of such a vaccine will require testing in animals, hence the importance of developing an animal model.
The Rotterdam experiments also cleared up some confusion that developed early in the search for the disease’s cause. German researchers initially identified a paramyxovirus (ultimately determined to be a metapneumovirus) in one of the first patients with SARS and experts initially suspected that it was the cause of SARS, or at least a contributing factor.
Osterhaus said Wednesday that his team infected monkeys with the metapneumovirus alone and with a combination of the metapneumovirus and the coronavirus.
Animals infected with the metapneumovirus developed only very mild respiratory symptoms, not the SARS symptoms. Animals infected with both viruses developed symptoms that were no more severe than those of animals infected with only the coronavirus.
“The conclusion today is that the coronavirus alone is capable of causing the typical [SARS] symptoms,” Osterhaus said.
The new virus was officially named “SARS virus” by WHO and its member laboratories. Some researchers had wanted to name it after Dr. Carlo Urbani, the Italian physician who first recognized the syndrome and who later died from it.