With increased air travel, the emergence of infectious diseases anywhere in the world is a global concern. A recent outbreak garnering attention is the emergence of a SARS-like virus in the United Kingdom (1). Many symptoms of this new virus, including cough, headache, and muscle ache, are shared with other more common illnesses. However the symptoms that inspired its name are less general: a fever of over 100.4 degrees Fahrenheit (38.0 degrees Celsius) and difficult, abnormal breathing. SARS is as an acronym for Severe Acute Respiratory Syndrome (2) and is caused by a cell-infiltration machine: a virus. The precise source of the new virus and its mode of transmission are still unknown, but some believe that it may be transmitted from animals due to its similarity to a known bat virus (1,3). Viruses that affect animals can occasionally be transferred to humans that come in contact with an infected animal, and this transmission of a pathogen from an animal to a human is known as zoonosis. Some common zoonotic diseases are Rabies, Malaria, Yellow Fever, and West Nile. The original SARS virus is thought to have originated in civet cats and then transferred to humans (14).

Figure 1. Digitally-colored image of the bronchitis virus, taken with a high-powered microscope.  This virus belongs to the same family of viruses as SARS-CoV.

Classic SARS

SARS was introduced to the world during the 2002-2003 outbreak centered in China, which began when a patient presented with atypical pneumonia. In the province where the first case occurred, people live in close proximity with animals, making it a breeding ground for new viruses. Infected people then spread the virus while traveling from one city to another. Soon there were an estimated 8,000 cases and 750 deaths around the world (2). This outbreak highlighted a major pitfall of globalization, as the virus spread from China to greater Asia, Europe, Africa, and North and South America (2) in less than two months (10), owing the speed of its spread to the prevalence of international air travel. The SARS virus causes a devastating pneumonia with a 10% mortality rate (4). In response to this SARS outbreak, the World Health Organization issued a global health alert for the first time in history (13).

SARS: New Emergence

While similar in many ways, the new SARS-like virus is still different from the original. So far, this newly emerged virus has reportedly infected fifteen people, killing nine since the fall of 2012 (1). This is a relatively low incidence rate, an indication that the virus is not spreading from person-to-person. This is supported by the fact that not all members in the household of an infected individual have gotten sick. Symptoms include lung infection and kidney failure. This time patients are clustered primarily in Jordan (1), Saudi Arabia and Qatar (11). The outbreak in the Middle East led the British government to preemptively test sick people returning from the Hajj, the holy Muslim pilgrimage, which brings people to the city of Makkah (Mecca), located in Saudi Arabia (12). Other health care regulators have been testing old patient samples to determine if the new SARS-like virus is actually novel or if it has been present in people before, but is only now presenting and being identified (11). The genes of the SARS-like virus are similar to those of a virus that infects bats, suggesting a zoonotic transfer. However, the genetic similarities are not enough to determine whether transmission to humans happened directly, through fruit contaminated with infected bat feces, for example, or indirectly by bats first infecting another organism that subsequently infected humans (12).

Attacking Our Bodies

But how does the virus interact with our bodies? The SARS-corona virus (SARS-CoV) is spread by respiratory droplets produced when people sneeze or cough (5). These droplets then settle on the mucous membranes of the eyes, nose, or mouth. The virus can survive on hands, tissues, and other surfaces for over six hours, allowing people to come into contact with the virus long after the infected individual has gone (2). Once in the body (Figure 2, step 1), the virus comes into contact with the cells that line our noses, mouths and throats, which can become infected. The virus binds to the outside of the cell (Figure 2, step 2) and is swallowed by the cell into a compartment called the endosome (Figure 2, step 3), from which it can escape and enter the interior of the cell (Figure 2, step 4). The SARS-CoV then uses our own cellular machinery to copy itself and to spread to other cells. SARS-CoV can go from the nose and throat to infect cells in the intestines, kidneys, and rectum, as well as neurons and immune cells (6). Infected cells attempt to recruit help from the immune system by releasing special signaling proteins. But if the levels of these proteins become too high, they can actually damage tissues. In a SARS-CoV infection, the lungs suffer the most damage, which can cause atypical pneumonia and other complications (6).

Figure 2. Illustration depicting how SARS-CoV interacts with our bodies.

Playing Defense

There are, however, defenses against the infection. The signaling proteins that can cause complications are also part of our bodies’ defense system. While the prolonged release of these signaling proteins can cause damage, they ultimately mobilize our bodies’ defenses by recruiting immune cells, called killer T cells, to the area. These cells can specifically recognize the SARS-CoV and kill cells that are infected, thus shutting down the virus-manufacturing centers. Another form of defense is antibodies. These proteins coat the outside of the virus to prevent it from binding to and entering the cells.

Recently, an international team of researchers has developed a drug called amiodarone that inhibits SARS-CoV (7). Amiodarone, known by its brand name Nexterone (8), is normally prescribed to treat abnormal heart rhythms, but in 2008, scientists discovered that amiodarone can stop SARS-CoV after it escapes from the endosome in tests conducted in a laboratory (7). Unfortunately, these tests have not yet been tried in a clinic. Several other anti-SARS compounds, including aescin, reserpine, and valinomycin, are being investigated by scientists (15). While these studies have not yet been done in animals or people, and there is no vaccine against SARS-CoV, by continuing to study how the virus works, scientists, doctors, and public health officials will be better equipped to handle the next serious outbreak. Although the 2002-2003 SARS epidemic caused widespread panic, the lessons learned from it left the world more prepared for future outbreaks.

Patrice Darby is a PhD student in the Biological and Biomedical Sciences Program at Harvard University.

References

Photo: “The Infectious Bronchitis Virus: a coronavirus in the same family as SARS-CoV.” Dr. Fred Murphy and Sylvia Whitfeild. Centers for Disease Control and Prevention. Public Health Image Library (PHIL). #15523. <http://phil.cdc.gov/phil/details.asp>.

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