The deadly SARS virus may possess the capacity for rapid and unpredictable evolutionary change, suggests recent research conducted at the University.
One of the genes in SARS is a mosaic of pieces cobbled together from several prior parents, ecology and evolutionary biology Prof. David Mindell and Rackham student Joshua Rest report in the journal Infection, Genetics and Evolution.
This process of mixing and matching, known as recombination, allows viruses to inherit the functions of several parents, unlike most viral genes that are direct clones from one parent virus.
If future recombination events occur, they could allow SARS to undergo sudden changes in function and behavior, Mindell said.
“Recombination is an important evolutionary mechanism,” he said. “It accomplishes for viruses what sex can accomplish for vertebrate animals.”
By studying the evolutionary tree of SARS, or Severe Acute Respiratory Syndrome, Mindell and Rest also showed that the family of viruses to which SARS belongs, coronaviruses – so named because their spiked surfaces resemble a crown of thorns – have a history of jumping from species to species. SARS is believed to have originated in birds, and may have moved from poultry or game birds to human hosts.
SARS first emerged in the rural Guangdong province of China in April of this year and spread when a physician infected with SARS traveled to Hong Kong and transmitted the virus to others staying in his hotel. SARS cases have occurred in 29 countries and have caused 813 deaths, with the largest outbreaks experienced in Hong Kong, Singapore, Taiwan and Toronto, as reported by the World Health Organization.
Only eight confirmed cases have occurred in the United States, with no confirmed cases in Michigan, according to the Centers for Disease Control and Prevention.
Although WHO pronounced the SARS epidemic contained in early July, many experts worry that SARS will recur.
“We’ve never had an experience where we’ve been able to terminate so quickly the spread of an infectious agent,” epidemiology Prof. Arnold Monto said. “It seems almost too good to be true, and we’re worried that it is too good to be true.”
Carl Simon, director of University Center for the Study of Complex Systems, who models infectious disease transmission, said respiratory illnesses commonly recur in a seasonal pattern. For instance, the deadly influenza epidemic of 1918 – which killed about 20 million people worldwide – began with a small outbreak the previous year that seemed to have been contained.
However, SARS differs significantly from other known respiratory illnesses, including other human coronaviruses, Monto said. “We cannot conclude as yet that it will be seasonal like our other respiratory diseases,” he added.
“There’s a huge question about what’s going to happen next year,” Simon said. “And boy, no one knows.”
To prepare for a possible recurrence, the University will reconvene its SARS task force that handled issues during the epidemic, said Robert Winfield, director of University Health Service. Next month, the task force will meet to discuss and implement public health measures for prevention and containment, especially those recommended by the CDC in a recent document on SARS preparedness.
The possibility of SARS’ return keeps research like Mindell and Rest’s in the spotlight.
“These findings are important first and foremost because the SARS virus is a threat to human health,” Rest said.
Since coronaviruses also cause minor illnesses ranging from stomach upsets to the common cold, the research will have relevance even if SARS itself never reappears, he said. Coronaviruses “are a group of viruses we probably should have put effort into understanding before, because they’re an important part of human biology.”