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Evolutionary epidemiology and Covid-19

I don’t usually teach evolutionary medicine in the Spring. In fact, I was originally scheduled to be in Kauai, hiking the Kalalau trail with a group of wilderness medicine students this April. Alas, that trip, and this year’s whole wilderness medicine elective, were not to be. Many students who would otherwise be scheduled for clinical rotations have found their schedules upended as well. I decided to open up my Ev Med elective, and make it entirely online, to help students, and me, get through this unexpected event. This elective will be a little different from previous ones. It will be (almost) entirely focused on COVID-19 with frequent detours to other topics.The COVID-19 pandemic gives an opportunity to highlight the relevance of an evolutionary approach to medicine.

Students will be asked to start by watching this video by Vaughn Cooper:

The fact the the SARS-COV2 virus (responsible for the COVID-19 infection) is evolving at a fairly rapid clip gives epidemiologists the ability to track its spread throughout the globe.

The good folks at NextStrain.org have done a beautiful job of collecting and displaying this massively important information, all made possible by the ability to rapidly sequence the genomes of SARS-COV2 isolated from sick – and in some cases, deceased– patients.

From their site: NextStrain.org provides “real-time snapshot of evolving pathogen populations and to provide interactive data visualizations to virologists, epidemiologists, public health officials and citizen scientists.” Students need to understand common descent and the role of mutation, and tree thinking to interpret the phylogenies that are depicted so vividly on Nextstrain.org

Among the first topics we will discuss: what are the consequences of SARS-CoV-2 evolving, both for epidemiological sleuthing  and for virulence? Can public health measures affect coronavirus evolution? Can we make SARS-CoV2 go extinct?

Tree thinking – Darwin style

Additional topics include host defenses. Patients with Covid-19 present with fever, cough, loss of appetite and loss of smell. These are part of the acute phase response, and can be considered host defenses against infection. How should physicians approach these symptoms and findings? Should we feed the patient who is not interested in eating? How aggressively should we intervene on fever, if at all? Is cough suppression a good idea? If medications suppress fever and the acute phase response, could they remain infectious for longer? How should physicians balance the public health need to prevent the spread of infectious particles versus the need to alleviate suffering on the part of individual patients?

Trade-offs. Immune defenses are critically important in fighting COVID-19 but can they go too far? How are immune trade-offs shaped by natural selection? What does it mean for drug development and patient care? We will focus on drug development aimed at treating cytokine storms. Will those newly developed pharmacological interventions be effective? Some intensivists are also worried about blood clotting in COVID-19 patients. Clotting is a tightly regulated process that is shaped by natural selection. Of course, clotting too involves tradeoffs; activated in the wrong way, clots kill, as exemplified by pulmonary embolism in hospitalized patients. How do these trade-offs affect the course and care of COVID-19 patients?

Mismatch and spillover events. Is it possible that our immune systems have not evolved appropriate defenses against COVID since it is a brand new (to us) pathogen? Also, many of us have novel conditions – allergy and obesity – that were rare in human evolutionary history; could these novel conditions leave us vulnerable to lethal viruses?  In both cases, we will explore the possibility that modern humans have not had enough time to refine our immune responses in the most optimal way.

Unanswered clinical questions. There is debate about whether the sickest COVID-19 patients have typical ARDS – acute respiratory distress syndrome – or something different. Some doctors have suggested that COVID-19 patients have something resembling high altitude pulmonary edema. We will talk about why high altitude pulmonary edema can resemble infection, and why our vulnerability to high altitude hypoxia might have evolutionary origins. We will discuss why our bodies respond to low oxygen availability in the way they do, and what this means for treatment of hypoxic COVID-19 sufferers.

Categories: Uncategorized

Joe Alcock

Emergency Physician, Educator, Researcher, interested in the microbiome, evolution, and medicine

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