The latest information from China and several other countries shows that the disease associated with the new coronavirus 2019-nCoV appears to be relatively mild compared to Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS). But this may not be a good thing for humans to curb the spread of new viruses on a large scale.
The question was raised in an opinionpiece article published January 24 in the New England Journal of Medicine, a leading medical journal. The authors are from the National Institutes of Health (NIH) and the Elams Medical Center in the Netherlands. They believe that if the new coronavirus has high transmission and is relatively pathogenic, coupled with a possible super-transmitter, it will be more difficult for humans to contain its large-scale outbreak.
Following the outbreak of SARS in 2002 and MERS in 2012, the new coronavirus became the third deadly coronavirus to break out in humans in the 21st century.
The article points out that the following questions are critical when faced with a new virus:
What is the shape of the disease pyramid?
What is the high proportion of people infected with the disease?
What percentage of people with the disease are hospitalized?
The answers to these three questions form the classic pyramid of disease surveillance.
Disease Surveillance Pyramid
As shown in the figure, the pyramids are “light or asymptomatic”, “severe” and “fatal” from bottom to top, and as the disease increases, so does the ability of humans to contain the virus.
This is because if the infection does not cause serious illness, the infected person is likely not to seek medical attention. Instead, they go to work and travel, which can spread the virus to contacts and even internationally.
The paper points out that the proportion of each of the three cases is not known for the 2019-nCoV. This knowledge gap makes it impossible to make a realistic assessment of the epidemic potential of the virus and complicates the response to the outbreak.
The article also mentions that much of the current human understanding of the relationship between the spread and lethality of respiratory viruses comes from the virus. The receptor-specific nature of avian influenza, a class of influenza virus, tends to shift from the lower respiratory tract to the upper respiratory tract, thereby reducing the burden of disease.
Two recent examples are H1N1 and H7N9. The H1N1 virus binds to upper respiratory tract receptors and causes relatively mild disease stoa The H7N9 virus binds to lower respiratory tract receptors and has a fatality rate of nearly 40%, but has so far caused only a few human-to-human cluster transmissions.
However, this inference may not apply to all viruses. Both NL63 and SARS-CoV use the same receptors, but are very pathogenic. NL63 usually causes only mild upper respiratory disease and endemic epidemics in populations. The SARS virus can cause severe lower respiratory diseases. Eventually, the virus, which has a fatality rate of about 11 percent, was contained by monitoring the syndrome, isolating the patient and isolating the contact. Therefore, the article points out that lethality and propagation are not necessarily related.
Pathogenicity and transmission of several viruses
However, from the experience of SARS and MERS, age and pre-existing diseases can affect the consequences. As a result, healthy people with less severe symptoms may not test for the virus, posing a significant risk to vulnerable people.
The article determines that the performance of non-serious diseases will affect people’s ability to contain the spread of the virus. If many infected people have no symptoms or only mild symptoms, it is much more complex to identify the chain of transmission and track the follow-on contact, which is an effective tool for containing SARS and Ebola.
The article concludes that while it is not yet known how powerful the new coronavirus is to spread from person to person, it appears to be less pathogenic than SARS (which may be coupled with transmission by super-transmitters in certain cases) that could lead to large-scale transmission.
Viruses that pose a lower health threat at the individual level can pose a higher risk at the population level and pose a challenge to the global public health system.
Therefore, the current aggressive response to the new coronavirus to track each patient and try to break the chain of transmission is correct.
The authors also suggest that epidemiological information on the pathogenicity and spread of the virus should be obtained through molecular testing and serum surveillance, thus supplementing the details in the disease surveillance pyramid and guiding the response to the outbreak.