SARS (severe acute respiratory syndrome) is an infectious disease that was first recognized in Guangdong Province, China in November of 2002. It then spread extremely rapidly to other regions within China, Hong Kong, Vietnam, Singapore, Taiwan, and Toronto, Canada in the early half of 2003. SARS is caused by a virus called SARS-associated coronavirus (SARS-CoV) and is characterized by severe, pneumonia-like symptoms which can be fatal. SARS-CoV was transmitted from person to person mainly through respiratory droplets produced when a person sneezes or coughs and through direct contact with a surface contaminated with infected respiratory droplets. Altogether, more than 8,000 people were documented to have been infected with SARS-CoV and over 800 died.
The global scientific response to SARS was unprecedented. Within weeks after the respiratory disease was first reported, the agent that causes the disease was identified, diagnostic tests were developed, and the entire genome of the virus was sequenced. Epidemiologists gathered evidence that the first people infected had had contact with wild game in the markets of Guangdong Province in China. It is likely that these individuals were infected through direct contact with infected animals that harbored very closely related coronaviruses. The virus then is thought to have mutated to adapt to its human host, and consequently human-to-human transmission became more efficient, setting off the SARS epidemic. Fortunately, the SARS outbreak was short-lived, and public health containment procedures and coordinated responses proved effective in preventing further spread of the disease.
SARS-CoV is a member of a class of viruses known as coronaviruses. The name coronavirus comes from its appearance under the microscope – the viruses have a spiky or crown-like (corona) appearance. Until recently, SARS-CoV was the only member of the coronavirus family known to cause death or severe respiratory disease in humans. The other viruses in this group cause mild upper-respiratory infections in humans and are associated with respiratory, gastrointestinal, and neurologic diseases in animals. One reason that SARS-CoV might have been more lethal than other coronaviruses is that it appears to interfere with an enzyme system in humans that is critical for regulating body fluid balance. Therefore, the virus could disrupt normal functioning of the lungs by blocking this enzyme system and allowing fluid to leak into the air sacs of the lungs, resulting in severe respiratory illness.
A new member of the coronavirus family emerged in the fall of 2012 in the Arabian Peninsula. The new virus has been named Middle East respiratory syndrome coronavirus (MERS-CoV). Although MERS-CoV is distinct from SARS-CoV, the disease caused by the new virus Middle East respiratory syndrome (MERS) is similar to SARS in that it causes a severe respiratory illness that can be fatal in humans.
The first and vast majority of cases of MERS have occurred in Saudi Arabia, although infections have been reported in several other countries in the region, as well as in a few European countries (likely due to travelers returning from the Middle East). As of late July 2013, approximately 90 cases of MERS infection were reported to the WHO, with about half of the cases resulting in death. MERS-CoV appears to spread between people who are in close contact.
Although there are currently no known human cases of SARS, it is still possible that another outbreak of SARS could occur. SARS-CoV still likely lurks in an animal host in the wild, and human contact with this animal(s) could again spark a SARS epidemic. Scientists have reported that the Chinese horseshoe bat is likely to be the animal that is the hiding place of the SARS virus. Genetic analysis of the virus in bats showed that it is closely related to the human SARS virus, although it is still not clear how the SARS virus was transmitted from bats to humans. Despite the large amount of knowledge that has been gained about SARS-CoV following the outbreak, there are still no vaccines or antivirals approved for preventing or treating SARS-CoV infections.
Currently, the greater concern is the potential for MERS-CoV to continue to spread. MERS is a severe disease in most infected people. Approximately half of the MERS-CoV infected people have died, which suggests that MERS-CoV is more deadly than SARS-CoV (although milder cases may not have been reported, so that it may not be quite as deadly as it presently appears). The source of MERS-CoV has not been identified, and questions remain as to precisely how the virus spreads from person to person. There is no vaccine or specific treatment for MERS.
Following the SARS outbreak of 2003, investigators in the Department of Molecular Virology and Microbiology (MVM) at Baylor College of Medicine (BCM) were awarded funds for development of a SARS-CoV research program as an expansion of the existing Virus Respiratory Pathogens Research Unit in a contract arrangement between BCM and the National Institutes of Health (NIH). The program focused on the pathogenesis of SARS-CoV infection and disease, development of a virus-like particle vaccine for SARS, and clinical trials of a SARS vaccine.
Results of an evaluation of candidate vaccines against the SARS virus were published by Drs. Robert Atmar and Robert Couch, along with colleagues at the University of Texas Medical Branch (UTMB) in Galveston, Texas. A whole virus inactivated vaccine was tested in ferrets and nonhuman primates and a virus-like particle vaccine was tested in mice. The vaccines provided protection against infection. However, the vaccines caused damage to the lungs of mice infected with the virus, so it is unlikely that these vaccine candidates would be developed for use in humans. It is possible that knowledge gained during this investigation could be applied to the development of a vaccine against MERS, should that become necessary.
For another approach, Drs. Peter Hotez and Maria Elena Bottazzi of the Departments of Pediatrics – Tropical Medicine and Molecular Virology and Microbiology and the National School of Tropical Medicine at BCM have received funding from the National Institute of Allergy and Infectious Diseases of the NIH to develop a recombinant protein-based SARS vaccine. Drs. Hotez and Bottazzi and their collaborators are basing their vaccine development on a segment of the SARS-CoV spike protein (a protein found on the outside of the virus that interacts with the host cell) known as the receptor binding domain. The idea is that the vaccine would stimulate neutralizing antibodies which would block the attachment of the virus to its receptor on the host cell, thus preventing infection by SARS-CoV. The vaccine would be used to avert a potential SARS outbreak as well as for biodefense preparedness in the event of SARS reemergence or use as an agent of bioterrorism.
- www.cdc.gov/ncidod/sars/factsheet.htm - Basic information about SARS from the CDC
- www.niaid.nih.gov/topics/sars/pages/default.aspx - Information about SARS from the National Institutes of Health
- www.who.int/csr/sars/en/ - Information about SARS from the WHO
- http://www.cdc.gov/coronavirus/MERS/ - Information about MERS-CoV from the CDC