SARS: THE FIRST NEW VIRUS OF THE 21ST CENTURY
In March 2003, a Chinese-American businessman died in Vietnam from a severe flu-like illness. Soon after, reports of a new disease, then termed "atypical pneumonia," made headlines around the world. Panic spread among the international community: nobody knew where this disease came from or what caused it. The disease was spreading rapidly, and it was deadly.
As the number of reported cases increased, the World Health Organization (WHO) issued a global warning regarding the disease, now called Severe Acute Respiratory Syndrome (SARS). Shortly thereafter, more information about the disease's origins and the reasons for its worldwide spread emerged.
How SARS began
The first cases of SARS probably arose in November 2002 in Foshan City, located in the Guangdong Province of China. The Chinese government did not publicize the outbreak right away, however. In February 2003, the Chinese Ministry of Health reported 305 cases, with five fatalities, of a disease that quickly deteriorated the patient's health and evolved to respiratory failure. About one third of those affected were health care providers.
SARS first gained attention outside of China in March 2003, when Dr. Carlo Urbani, a WHO official based in Vietnam, reported several cases of "atypical pneumonia" at the hospital where he worked. The first of these cases was the Chinese-American businessman. Following these reports, the WHO was finally able to trace the disease and account for its spread across so many countries. On March 29, Dr. Urbani himself died of SARS.
Following the SARS trail
Before going to Vietnam, the businessman had stayed in Hong Kong, on the ninth floor of the Metropole Hotel. At the same time, a doctor from Guangdong Province had been a guest on the same floor. The doctor had treated SARS patients in Guangdong prior to his visit to Hong Kong, thus carrying the disease out of Guangdong.
Shortly after the doctor's visit to Hong Kong, other people connected with the ninth floor of the hotel fell ill. It soon became clear that the Guangdong doctor had infected 12 other guests and visitors. Among them were a tourist from Toronto, a flight attendant from Singapore, the businessman who subsequently traveled to Vietnam, and a local Hong Kong resident, who was visiting an acquaintance at the hotel.
It can take up to 10 days for a person who is infected with SARS to actually get sick. Because of this long incubation period, guests of the hotel unwittingly carried the disease out of Hong Kong via air travel into Canada, Vietnam and Singapore. When these patients did get sick, their symptoms were so flu-like that they were not diagnosed right away. Patients' families and health care providers were exposed and became infected with the disease. Following the deaths of some patients, authorities in Canada and Singapore reported these cases to the WHO, which immediately issued the global alert.
Science uncovers the culprit
When it became clear that a new disease had surfaced, steps were taken to contain the illness and find possible causes. Since the infectious agent was unknown and existing treatments seemed to fail, hospitals resorted to old methods such as quarantine and isolating patients to prevent further spread.
Because the disease was new, scientific research was needed to develop diagnostic tools and treatments. The WHO launched a coordinated effort to identify the origin and cause of SARS, uniting eleven laboratories from around the world to work toward this goal.
On April 16, 2003, the laboratory network announced that it had found the cause of SARS: a virus.
Viruses are pieces of either DNA or RNA surrounded by proteins and often enveloped in a membrane. Unlike bacteria, viruses are not living and can only reproduce inside of cells they infect.
Each virus displays special "ligand" proteins on its surface. These proteins act as keys, giving the virus access to a cell by attaching to receptors on the cell's surface. Once inside, viruses hijack the cell's internal machinery to reproduce. When released from the cell, the new viruses attack other cells and continue the infection.
Viruses can mutate rapidly. In some cases, mutations enable them to invade cells they previously could not, sometimes even "jumping" from animals to humans. Scientists think that the SARS virus jumped to humans from another animal, possibly rats or the weasel-like civet cat, which is eaten as food in China.
In other cases, mutations make the virus more disruptive, which is why some strains of viruses are deadlier than others. These frequent changes make it difficult to create effective vaccines to protect humans against infection. This is why new influenza vaccines are recommended each year, before the onset of "flu season."
SARS and genetics: the sequence is key
Modern genetics and biotechnology enabled the working group to quickly pinpoint the cause of SARS. After determining the exact sequence of the virus's genome, which consists of a 29,727-base-long strand of RNA, scientists were able to classify SARS as a coronavirus. The coronavirus family, which also includes the influenza virus, is split into three groups. One group infects birds, whereas the other two infect mammals.
SARS was classified as a coronavirus because it shares the same basic set of genes with other members of this family. Scientists found enough differences between SARS and other family members, though, to conclude that SARS represents a new fourth group. This means that SARS probably did not evolve from a previously known virus.
Early and definite diagnosis of SARS is crucial if future outbreaks occur, especially during flu season. Without a reliable way to distinguish SARS from the flu or other respiratory diseases, all patients showing potential SARS symptoms would need to be isolated and treated accordingly. This could quickly overwhelm hospitals. With the virus's genome sequence now in hand, scientists can develop accurate diagnostic tests for SARS.
Treatment and prevention
Knowing the sequence of the virus will also help in treatment and prevention of the disease. Vaccines can be developed more rapidly if the sequence of a virus is known. To develop a vaccine, a milder version of the virus can be artificially recreated and injected into patients. The patient's immune system reacts by creating antibodies, which protect a person from future infection.
While a treatment for patients who are already sick has not yet been developed, knowledge of the genetic makeup will help to find ways to inhibit the virus. Already, sequence information has helped scientists predict the structures of key proteins involved in the virus's infectivity and reproduction. This information will aid those working to develop antiviral drugs that can be used to treat patients.
Can we go to China now?
On July 5, 2003, the WHO announced that the last human chain of SARS transmission had been broken, meaning that SARS may be contained among humans. In the months since, no new cases have been reported. According to the WHO, 8,422 people were affected up to August 7, 2003, and 916 had died. One in five of those affected was a healthcare worker.
People should still exercise caution because the origin of the virus remains unknown. This means that the virus may still exist in animals and once again jump over to humans, creating a new outbreak. Travel to regions that were affected by SARS is now considered safe, but it is wise to stay current on recent developments before heading off to these areas.
Funding for this feature was provided by the
Author: Monica Mendoza