15 April 2013
David Heymann

Professor David Heymann CBE

Head and Senior Fellow, Centre on Global Health Security


Since the outbreak of Severe Acute Respiratory infection (SARS) ten years ago, efforts to detect unusual severe respiratory disease have intensified. At the same time, there have been major advances in the development of diagnostic tests. This is a result of a major increase in the research and development budget for tests to diagnose unknown disease, and this investment was driven by the perception that anthrax and other organisms such as the smallpox virus will continue to be a bioterrorism threat.

When disease detection efforts are intensified, surveillance systems often become better at picking up illness that would have otherwise gone undetected until enough people developed the disease that an outbreak occurs and is noticed. Throughout history, mysterious severe respiratory infections that have resulted in death have emerged, but with new diagnostic tests it is also now possible to determine the cause of such disease, often soon after it is detected. 

Against this background, scientists and public health workers identified a new human infection last year - the novel coronavirus (nCoV) in a patient from Saudi Arabia. Further persons infected with the same virus have been identified since, and all appear to have links with the Middle East, suggesting that the virus is emerging in the region. Emergence of a virus such as nCoV in most cases occurs at the animal/human interface (any place where animals and people are in close contact, such as on farms, in forests or the home). At this interface, infectious agents that are often not causing illness in the animals are able to breach the species barrier and infect a person. In the case of nCoV, it does not appear that the virus is able to transmit easily from person to person – most of the cases have been single events, which suggests that each infection has thus far occurred at the animal/human interface. There has been a cluster of three cases, however, in the UK where two additional people were infected, probably by person-to-person spread. Studies have shown that the virus did not infect others in contact with the patient, such as the health workers who took care of the patients. But vigilance must be maintained each time a human is infected in order to determine if for some reason – usually a mutation – the virus becomes more able to spread from person to person and thus cause an epidemic. 

Several scientists and epidemiologists have suggested that the animal source of nCov could possibly be a bat because studies have shown genetically similar viruses harboured by bats. But this remains a hypothesis and is yet to be proven by research that is being planned or is underway in the Middle East. What is most concerning when a new virus emerges is not what is known about it, but what is not known, including its potential to spread from person to person and eventually becoming a common disease in humans, as occurred after the emergence of AIDS from non-human primates. 

Recently, a new influenza virus has been detected in humans in China – the H7N9 influenza A virus. All new influenza viruses are thought to come from waterfowl, and once they have emerged in humans, either directly or from another animal infected by waterfowl, their potential is unknown. It appears that like the nCov, most of the H7N9 infections to date have been from an animal source, and no clusters of infection suggestive of human-to-human transmission have been reported.

Studies in China appear to have shown that the virus can be found in certain types of birds and in chickens, and that it is not causing severe disease in them, although these results are preliminary and will be used in daily risk assessments conducted by the World Health Organization (WHO) and its partners. Influenza viruses are very unstable and mutate easily as they reproduce.  Scientists and epidemiologists will continue to study this virus to determine whether there are any signs that it is changing in a way that could cause an epidemic or pandemic. But no predictions are possible because mutations occur randomly and scientists do not yet understand to what extent this particular virus has spread among birds and/or animals. 

Virus emergence such as is occurring with nCoV and H7N9 influenza A, are events that must be regularly and thoroughly assessed for risk, and require research to better understand their epidemiology and potential to cause harm. Because the increase in detection efforts and the ability to diagnose took place during the past ten years since SARS, we have no baseline with which to compare what is going on today with what went on before SARS. It is certain that there have been similar emergence events in the past, but there is no frame of reference within which to assess how frequently they occurred and whether what we are seeing today is any more remarkable than what has occurred over the past century. As it remains important to learn about the potential of any newly identified virus to cause harm, scientists and epidemiologists will continue to work in partnership with WHO to do the research required to completely assess and manage today’s risks.  

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