In November 2002, the first case of an unusual pneumonia was reported in southern China. Over just the next few months, the mystery illness spread to more than 24 countries inNorth America, South America, Europe, and Asia as public health officials scrambled to identify and contain this serious health threat. Although 8,098 people became sick with SARS during the outbreak, only eight people in the United States were diagnosed with the infection, and all had traveled to other parts of the world affected by SARS.
A decade later, another SARS-like illness emerged in the Middle East. Although the latest virus stopped short of triggering a global panic, it left a lot of people wondering what happened to SARS and why these viral outbreaks occur.
What Happened to SARS?
Severe acute respiratory syndrome, or SARS, is caused by a type of virus called a coronavirus. Most people will be infected with a coronavirus at some point in their lifetime. The coronaviruses that infect humans generally cause mild to moderate upper-respiratory infections. These viruses, however, can also infect animals. Although most infect just one or a few closely related species at a time, the SARS virus infected both people and animals, including monkeys, cats, dogs, and rodents.
In 2013, research conducted by an international group of scientists published in Nature suggested the most reliable evidence to date is that SARS could be traced back to the Chinese horseshoe bat. The team of researchers argued it's very conceivable that SARS spread from these bats directly to people.
SARS then quickly spread among humans through close person-to-person contact, specifically respiratory droplets that form when people talk, cough, and sneeze.
Within two to seven days, people infected with SARS typically develop a high fever and other flu-like symptoms, such as headache, diarrhea, and overall achiness. Most worrisome is that the virus can progress to pneumonia or other serious respiratory illnesses.
Will SARS Return?
In late July 2003, the World Health Organization concluded the SARS outbreak was over. Since then, nine cases of SARS infections have been reported, but they occurred as a result of laboratory accidents in Singapore and Taiwan and from exposure to an animal source. No other cases of SARS have been identified anywhere else in the world. Research published in 2013 in the Journal of Infectious Diseases concluded that, by all accounts, SARS seemed to be gone.
For the virus to reappear, the World Health Organization stated it would have to come from one of three sources: an animal, another laboratory accident, or from undetected transmission among people. Although the virus may be a thing of the past, experts cautioned that the lessons learned from the global outbreak should not be forgotten.
What Triggers an Outbreak
How and why a virus emerges can involve a number of factors, including human behavior, changes in the environment as well as accidental changes, or mutations, to viruses.
Viruses need a host to survive and reproduce. After infecting a host, viruses inject their genetic material into cells. This genetic material, which is either encoded in DNA or RNA, carries instructions on how to make more viruses that will spread within the host.
Although otherwise healthy people can develop antibodies to fight infection and prevent re-infection, viruses have the ability to change and evolve so they, too, can survive.
Viruses that use DNA to reproduce themselves mutate more slowly because the process involves a proofreading of the genetic material being copied. So DNA viruses do not change very much. In contrast, RNA viruses skip this proofreading process. As a result, mistakes in copying the genetic information, or mutations, occur more often. SARS is one such RNA virus.
Animal viruses can mutate and develop the ability to infect people. Aside from SARS, a few other pandemics are believed to have been triggered by viruses that were once only found in animals, including HIV and avian, or bird flu.
Is MERS the New SARS?
Scientists are still working to identify the animal source of the latest coronavirus to make headlines, known as Middle East Respiratory Syndrome Coronavirus, or MERS.
MERS first emerged in September 2012 in Saudi Arabia. Unlike SARS however, MERS did not spread to the United States and did not trigger a global panic. A 2013 study published in The Lancet revealed some key differences.
Although both MERS and SARS are coronaviruses that generally cause fever and chills, and have the potential to lead to pneumonia, MERS can also cause kidney failure.
MERS has a longer incubation period, while SARS typically progresses to respiratory failure more quickly. The researchers, led by Ziad Memish, Saudi Arabia's Deputy Minister for Public Health, also noted that MERS is more likely to affect people with other health problems, such as diabetes, kidney disease, and heart disease. They concluded that MERS, which has resulted in 68 deaths as of November 2013, would not become a global threat in the same way that SARS did.
Although MERS did not cause a pandemic, SARS did demonstrate how quickly a new virus could emerge and spark a global health crisis. Among the lessons learned from the 2003 outbreak is that identification and containment of viruses is crucial to preventing the return of SARS or another viral epidemic.