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Emerging Infectious Threats Challenge Past Assumptions and Future Certainties
By Kelly M . Pyrek
The world has grappled with the double-edged sword of a pandemic and the potential of re-emergence of established diseases , made more problematic by the beginning of influenza season .
As Morens and Fauci ( 2020 ) observe , “ Unimagined just a few short months ago , the ongoing COVID-19 pandemic has upended our entire planet , quickly challenging past assumptions and future certainties . It possesses simultaneously three characteristics that have allowed it to render an historic assault on the human species , triggering a virtual global lockdown as the only weapon against uncontrolled spread . It combines the characteristics of being a virus that to our knowledge has never before infected humans in a sustained manner , together with its extraordinary efficiency in transmitting from person to person and its relatively high level of morbidity and mortality , especially among seniors and those with underlying co-morbidities . It indeed is the perfect storm of an emerging infectious disease .”
The experts refer to the concept of a “ pandemic era ,” explaining that , “ Since there are four endemic coronaviruses that circulate globally in humans , coronaviruses must have emerged and spread pandemically in the era prior to the recognition of viruses as human pathogens . The severe acute respiratory syndrome ( SARS ) coronavirus ( SARS-CoV ) emerged from an animal host , likely a civet cat , in 2002-2003 , to cause a near-pandemic before disappearing in response to public health control measures . The related Middle East respiratory syndrome ( MERS ) coronavirus ( MERS-CoV ) emerged into humans from dromedary camels in 2012 but has since been transmitted inefficiently among humans . COVID-19 , recognized in late 2019 , is but the latest example of an unexpected , novel , and devastating pandemic disease . One can conclude from
As COVID-19 is caused by a novel virus ( SARS-
CoV-2 ) producing a spectrum of disease whose clinical , pathologic , and epidemiologic patterns have never before been observed , we are gaining insights only incrementally .”
this recent experience that we have entered a pandemic era . The causes of this new and dangerous situation are multifaceted , complex , and deserving of serious examination .”
Over the course of much of 2020 , public health experts have wrestled with understanding SARS-CoV-2 and issuing consistent , effective policies and procedures to combat the enemy . Acknowledging the difficulty of wrangling wiley microorganisms , Morens and Fauci ( 2020 ) note , “ As COVID-19 is caused by a novel virus ( SARS-CoV-2 ) producing a spectrum of disease whose clinical , pathologic , and epidemiologic patterns have never before been observed , we are gaining insights only incrementally . At some time in the future we will be better able to compare and contrast COVID-19 to other important emerging diseases ; however , at this time we are still just entering a steep learning curve that will surely keep surprising us as we struggle to control what is already among the deadliest pandemics of the past century .”
Emerging infectious diseases encompass four categories : newly emerging , re-emerging , or “ deliberately emerging ,” ( associated with bioterrorism ), and “ accidentally emerging ” human-generated diseases , such as repeated emergences of vaccine-derived polioviruses ( VDPVs ) resulting from naturally occurring back-mutations of live virus vaccines , as well as a live human-engineered vaccine that escaped to cause a new epizootic disease : naturally transmitted vaccinia . A fifth category of “ de-emerging ” diseases is significant , according to experts , because it emphasizes the importance of responding to disease emergence threats with countermeasures ; these diseases are those that have been eliminated or even eradicated or that are in the process of elimination and / or eradication .
Pathogens with zoonotic origins , and the threat of host-switching , remains of concern .
As Morens and Daszak , et al . ( 2020 ) confirm , “ We have actually been watching such dramas play out in slow motion for more than a millennium in the case of pandemic influenza , which begins with viruses of wild waterfowl that host-switch to humans and then cause human-to-human transmission . A bird virus thereby becomes a human virus . Coronavirus emergence takes a different trajectory , but the principles are similar : SARS , the Middle Eastern respiratory syndrome ( MERS ), and COVID-19 all apparently have their origins in enzootic bat viruses . The parallels between the two SARS viruses are striking , including emergence from bats to infect animals sold in live-animal markets , allowing direct viral access to crowds of humans , which exponentially increases opportunities for host-switching . Such live markets have also led to avian epizootics with fatal human “ spillover ” cases caused by nonpandemic , poultry-adapted influenza viruses such as H5N1 and H7N9 . One human cultural practice in one populous country has thus recently led to two coronavirus near-pandemics and thousands of severe and fatal international cases of ‘ bird flu .’”
And as Morens and Fauci ( 2020 ) observe , “ One of the most important unanswered questions we face in the ongoing COVID-19 pandemic relates to the evolutionary potential of human-adapted SARS-CoV-2 . Will it , similar to human IAVs in recent centuries , evolve to persist as a permanent human pathogen by mutating to escape the population herd immunity it creates ? And if it does persist , will it attenuate over time , as the four endemic coronaviruses may have done centuries ago ? Or , on the other hand , will it increase in pathogenicity as the pandemic H3N2 IAV has done over the past 52 years ? Because SARS-CoV-2 lacks a segmented genome , we are spared at least