In 2002 a new human respiratory disease emerged in southern China. The following year one of the doctors who had been treating patients travelled to Hong Kong, where he became ill and died. Subsequently, people who had stayed in the same hotel as the doctor travelled to Singapore, Vietnam, Canada and the US, taking the infectious agent with them. The epidemic of severe acute respiratory syndrome (SARS) was under way.
The signs and symptoms of SARS resemble those of influenza and include fever, aching muscles, sore throat, cough and shortness of breath. About 90 per
Large, complex virion
Members include smallpox and vaccinia viruses
Genome: ssRNA (plus strand)
Capsid symmetry: helical
Enveloped virion with a corona of glycoproteins
Includes SARS coronavirus
cent of patients recovered, but for the remainder the infection proved to be lethal. These were mainly individuals who had an underlying condition such as diabetes, heart disease or a weakened immune system. On the face of it SARS is a respiratory tract disease, but in many patients the infection spread to other parts of the body. Diarrhoea developed in some patients and the virus was shed in the faeces and urine for several weeks.
The causative agent was found to be a new coronavirus (Figure 21.10). No natural reservoir for the SARS coronavirus has been found, but coronaviruses with very similar genome sequences were isolated from animals sold in markets in the region of China where the first SARS cases appeared. Antibodies to these viruses were found in many workers in the markets, but none of the workers had any history of SARS. A similar virus has also been isolated from several bat species. It is likely that coronaviruses have repeatedly crossed into humans from other mammalian species, but in the majority of cases the virus has lacked the ability for efficient human-to-human transmission. It would seem that the SARS coronavirus evolved from a rare virus that had this ability.
The SARS outbreak was brought under control by quarantine measures, but only after there had been over 8000 cases with nearly 800 deaths.
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