Last february, the WHO released the list of priority infectious diseases. The list included Disease X, a potentially serious illness caused by an unknown pathogen in the future.

In May, The Johns Hopkins Center for Health Security published a new report  with the conclusions of a study conducted to elucidate the characteristics of naturally occurring microorganisms that constitute a global catastrophic biological risk (GCBR).

Those events in which biological agents—whether naturally emerging or reemerging, deliberately created and released, or laboratory engineered and escaped—could lead to sudden, extraordinary, widespread disaster beyond the collective capability of national and international governments and the private sector to control. If unchecked, GCBRs would lead to great suffering, loss of life, and sustained damage to national governments, international relationships, economies, societal stability, or global security.

These are the traits of a GCBR-level pathogen:

• efficient human to human transmissibility,
• an appreciable case fatality rate,
• the absence of an effective or widely available medical countermeasure,
• an immunologically naïve population,
• virulence factors enabling immune system evasion, and
• respiratory mode of spread.
• Additionally, the ability to transmit during incubation periods and/or the occurrence of mild illnesses would further augment spread.

The conclusion is that the most probable naturally occurring GCBR-level threat that humans face is from a respiratory borne RNA virus.

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Image © 2018 by Johns Hopkins University