What is severe acute respiratory syndrome (SARS)?

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A newly recognized type of pneumonia, caused by a novel coronavirus, that may progress to respiratory failure and death.
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Causes and Symptoms

SARS first received worldwide attention in February, 2003, after a Chinese physician from Guangdong Province and twelve other guests at a hotel in Hong Kong became ill. Subsequent investigation of cases traced the illness back to November, 2002, when a businessman from Guangdong Province developed the new disease and soon died. Using electron microscopy, molecular techniques, and tissue cultures, researchers have identified a coronavirus in a variety of specimens from patients with SARS. Glycoprotein spikes on the outside of the envelope surrounding the viral capsid give the appearance of a crown, or corona, and make possible the identification by electron microscopy. The virus was cultured from lung and kidney specimens obtained at autopsy of the Chinese physician using African green monkey kidney cells. Pure cultures of the coronavirus have been inoculated into monkeys, producing pneumonia. With Koch’s postulates fulfilled, researchers are confident that the coronavirus is the causative agent.

Human studies have revealed antibodies to this coronavirus only in SARS patients, suggesting that this is a new type of infection. Similar studies in animals have shown that SARS antibodies are present in wild animals, including the masked palm civet, raccoon dog, and ferret badger. While these animals have been found to host the SARS coronavirus, a 2006 study suggested that the natural reservoir host of SARS is likely the horseshoe bat. The crowded, unclean markets of Guangdong Province, which sell wild animals for human consumption, may have provided the opportunity for the virus to infect humans.

After an incubation period of two to sixteen days after exposure, patients develop fever, chills and rigors, myalgia (muscle pain), cough, headache, and dizziness. Less common symptoms are sputum production, sore throat, nausea and vomiting, and diarrhea. Radiographs and high-resolution computed tomography (CT) scans of the chest show ground-glass opacities and unilateral or bilateral air-space consolidation. Laboratory findings early in the illness often include lymphopenia, thrombocytopenia, and a variety of serum enzyme (lactate dehydrogenase, creatinine kinase, and alanine aminotransferase) elevations distinguishing SARS from pneumonia caused by usual bacterial pathogens.

SARS is often progressive in severity and is highly infective, especially for family members and health care workers. During the 2003 outbreak, the disease spread to many countries, with more than eight thousand cases and nine hundred deaths worldwide. The overall mortality rate was about 5 percent. Researchers wondered whether this respiratory illness would follow the seasonal pattern of similar viral illnesses, such as influenza. A SARS case diagnosed in Guangdong Province in January, 2004, led the Chinese government to order the mass slaughter of civets and rats in the hope of containing the disease.

Besides the livestock and human tolls, SARS inflicted economic and political damage. During the outbreak months in 2003, Asian countries saw a financial loss of roughly $28 billion. For the first time, the World Health Organization (WHO) issued an advisory suggesting that travelers avoid parts of the world infected with SARS. North American–based airlines cut 10 percent of their flights to Asia, resulting in a 60 percent drop in tourism. In Canada, China, and the United States, sporting events, public gatherings, film productions, religious services, and parades were canceled because of fears concerning SARS. An interesting footnote to the SARS legacy occurred in June, 2006, when Chinese researchers revealed that at least one of the reported SARS deaths in China during April, 2003, was actually the result of H5N1 avian influenza; raising the possibility that other cases and deaths attributed to SARS may have actually been human cases of H5N1 bird flu and that the Chinese government covered up the possibility that two pathogens were creating simultaneous outbreaks in order to avoid further economic disruption.

Treatment and Therapy

No specific diagnostic test for SARS is available, hampering early diagnosis and treatment. SARS cases can be suspected but not reliably distinguished from other types of pneumonia. Thus far, no antiviral agent has been found to be active against the SARS virus, and initial empiric therapy with antibacterial and antiviral agents has been directed at other pathogens that cause pneumonia that is indistinguishable from SARS.

Supportive measures directed toward respiratory failure, often provided in an intensive care unit, are the mainstays of SARS therapy. In some cases of progressive pneumonia with respiratory failure, corticosteroid therapy has been used. Because of the alarming infectivity and spread of SARS, precautions against airborne droplets (respirators) and direct contact (gowns and gloves) are recommended. Despite such measures, spread occurred, probably because of improper techniques used by inadequately trained personnel.

Perspective and Prospects

A coronavirus was first cultured from an adult patient with a common cold in 1965. It is now recognized that coronaviruses may cause up to 30 percent of common colds, but before SARS coronaviruses rarely produced pneumonia. These viruses also cause disease in a wide variety of animals, but usually in only one species. It is unclear how the SARS agent jumped from animals to humans. Furthermore, while some wild animals have been identified as having prior infection by the virus, the natural host remains uncertain. A more complete understanding of these issues will improve the chances of eliminating the disease from humans. Fortunately, only a few cases of SARS have been reported in the first few years of the twenty-first century, and these cases have been in laboratory workers or individuals directly exposed to civet cats. On May 18, 2004, the World Health Organization (WHO) reported that an outbreak in China was contained and that human-to-human spread had apparently ceased.

Extraordinarily rapid research has already produced sequencing of the SARS coronavirus genome. With this knowledge, molecular diagnostic techniques have been developed and should produce rapid and accurate diagnostic tests that will be widely available. Thousands of antiviral agents are being tested for activity against the virus, and new antivirals are being developed. Vaccines are available for some animal coronaviruses, and a SARS vaccine may be developed. In the meantime, there is hope that infection control and quarantine measures will be able to limit the spread of SARS.

The WHO reported that, in September 2012, a new SARS-like virus, called novel coronavirus, or nCoV, emerged in Saudi Arabia, Jordan, Qatar, Britain, Germany, and France. As of May 2013, twenty patients died of the virus out of forty confirmed cases. Although it seemed that the virus only spread between humans after extended, close contact, scientists are closely monitoring the virus for indications that it could be transmitted between people more easily and cause a pandemic. Researchers are also looking for possible treatments for nCoV, including a combination of ribavirin and interferon-alpha-2b, two antiviral medications that have shown early promise in a study published in April 2013 in Scientific Reports..

Bibliography

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Kleinman, Arthur, and James L. Watson, eds. SARS in China: Prelude to Pandemic? Stanford, Calif.: Stanford University Press, 2006.

Ksiazek, Thomas G., et al. “A Novel Coronavirus Associated with Severe Acute Respiratory Syndrome.” New England Journal of Medicine 348 (May 15, 2003): 1953–1966.

Lee, Nelson, et al. “A Major Outbreak of Severe Acute Respiratory Syndrome in Hong Kong.” New England Journal of Medicine 348 (May 15, 2003): 1986–1994.

McIntosh, Kenneth, and Stanley Perlman. “Coronaviruses, Including Severe Acute Respiratory Syndrome (SARS)-Associated Coronavirus.” In Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases, 7th ed., edited by Gerald L. Mandell, John F. Bennett, and Raphael Dolin. New York: Churchill Livingstone/Elsevier, 2010.

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