April 02, 2003
Silent Carriers May Be Spreading Severe Acute Respiratory Syndrome

A forthcoming New Scientist article reports the greatest fear of SARS (Severe Acute Respiratory Syndrome) researchers is the possibility of asymptomatic "silent carriers" may make SARS uncontainable

But if people can harbour and transmit the virus while while remaining healthy, or showing few symptoms, it will be much harder. "If there are silent carriers, it will be virtually impossible to contain," warns Osterhaus. This issue is now the focus of research, says Heymann. A lab test for SARS would give a huge boost to surveillance and containment efforts.

If the disease reaches India or some other country where few people have access to an organized healthcare infrastructure then the disease is going to be extremely difficult to contain anyhow. We could quickly reach a point where many countries stop allowing travel from countries where the disease is spreading unchecked.

Some people may not be entirely asymptomatic but they might have symptoms too mild to cause a person to seek medical attention.

Lucien Abenhaim, who as director-general for health is France's equivalent of surgeon-general, noted however "we know now that there are minor forms of the illness," meaning that people can be infected but have only minimal symptoms.

Hopefully the silent carrier fear will not pan out. But even if it doesn't it is by no means assured that SARS can be contained at this point.

SARS demonstrates the value of speedier methods to isolate and characterize pathogens. Technologies under development to make nanodots and other nanotech sensor approaches for biological material promise someday to speed up the development of defenses against new infectious agents by orders of magnitude. Advances in biotech are already evident in the response to SARS. It took many months to identify and characterize the cause of Legionnaire's Disease back in the 1970s. The pace of the advance in the SARS investigation has been much more rapid. The scientists working on the cause of SARS have already focused their attention on a coronavirus after an initial suspicion that a paramyxovirus might be the cause. Now scientists are reporting that SARS might have been come about from the mixing of DNA from coronaviruses from different mammalian species.

Canadian scientists racing to find the cause of SARS say it appears to be a mutant strain of coronavirus with bits of human, cow and mouse virus scrambled into its genetic code.

The likely way this happened was that a single animal or human was infected by human and animal coronavirus strains at the same time. Different kinds of coronavirues in the same cell swapped genes to create a new and more virulent hybrid. Separately, other scientists have shown that cross-species mixing of coronaviruses can create new and more infectious forms of virus.

Now, in a simple overnight experiment, researchers transformed a coronavirus that is lethal to cats into one that infects mouse cells by replacing a single gene1.

The genetic code of the coronavirus that is suspected of causing SARS is expected to be approximately 30,000 DNA base pairs in length. Scientists are working with isolates of the SARS coronavirus to sequence it. Once it has been refined into a pure enough form to be DNA sequenced the current equipment for DNA sequencing could read its code within a single day. However, sequencing is normally done several times to check for errors and so this process can take a week or two. Where we are still lagging in speed is in the ability to then develop a vaccine or drug that can counteract the effect of SARS. The best prospect for development of an anti-SARS treatment in the short term is in the isolation of gamma globulin from the blood of those who have recovered from the disease.

Although no drugs have proved useful in treating the viral infection, Dr. Leung Ping-chung of Prince of Wales Hospital said Monday that doctors used gamma globulin from recovered patients to treat 20 severely affected victims

The success of the gamma globulin treatment raises the prospects of being able to reduce SARS deaths in industrialized countries should SARS reach pandemic levels.

The rate of scientific progress in investigation of the cause of SARS might be fast enough to stop the spread of the disease because tests may be developed to speed its detection. Though that the containment of SARS is by no means assured. Even if we manage to dodge the bullet this time there is no reason for complacency. If an influenza (which is probably more easily transmissible) of equal or greater lethality was to pop up then the odds of containing it with current technology and current public health practices would be much lower. Therefore even in the industrialized countries humanity remains quite vulnerable to new and more lethal forms of natural pathogens.

The New Scientist has a worthwhile SARS theme page with all their SARS articles.

Update: You can find all of the FuturePundit SARS posts in the Natural Dangers category archive. Also, you'll find my coverage of the economic impacts of SARS on my ParaPundit blog in the Political Economics category archive

Update II: To clarify: Note that in the event of an outbreak of SARS into wider populations that while gamma globulin may be able to save many lives in industrialized countries SARS would exact a far higher toll in less developed countries. Also, as is being demonstrated in East Asia right now the economic consequences of a SARS pandemic would be enormous. I've been posting a lot on SARS because its like we are out there on the edge of a precipice and it is not yet clear whether we are going to take the plunge.

Share |      Randall Parker, 2003 April 02 03:35 PM  Dangers Natural Bio


Comments
Patrick said at April 2, 2003 6:36 PM:

We could indeed reach the ironic stage where all the knowledge about viruses gained from AIDS research may stop a pandemic that would have ended up killing more people than AIDS has.

Jason said at April 4, 2003 12:18 AM:

It's interesting to speculate about what would happen if this disease were to hit India; however I would say that China, in terms of population and access to health care in the rural areas is not so different, except that the government is less likely to release information to the world. The Flu pandemic of 1918 had some similarities to this disease, notably that otherwise healthy people in the prime of their life seem to be victims. Imagining what could have happened during that pandemic had air travel been common brings nightmares. The mixture of coronaviruses from different animals mentioned above also sounds a little like flu; often new flu strains (which, coincidentally, often come from Asia and particularly China) are strains that make a jump from other animals (often birds) to pigs, get mixed up in the pigs and are then able to jump to humans. This disease could get much worse before it gets better; note also that Flu epi- and pandemics have historically happened approximately every 30 years and the last one happened in the late 60's....not that SARS is flu, per se, but this certainly mimics some of the killer influenza experienced in the last century.

Kendra said at August 9, 2015 3:50 PM:

What's really fascinating is looking back at this a decade later and remembering what it was like when the whole SARS scare was going around. Not only that, but to see the speculation about new variants compared with what actually happened in 2012/13. Check this out: http://coronamap.com/

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