Biology professor explains the spread of disease and how to protect yourself

I am grateful to the entire LC community for doing their utmost to reduce interactions and practice social distancing in an effort to slow the unprecedented pandemic we now face.  I hope that providing a quick primer on the dynamics of emerging infectious disease might help everyone remain resolute to do our utmost to slow the spread in our community. You can consider this a 5-minute sound bite from the first 6 weeks of Bio 370: Disease Ecology.

The rate at which new infections arise is related to transmission rates and what fraction of the population is susceptible or already infected.  

Transmission depends on contact rates between people and features of the virus or the host that make it more or less contagious.

Multiplying these together gives the rate of new infections, which means anything you can do to lower one or more of those numbers makes the overall number of new infections lower.  

We want the new infection rate to go down and spread out through time, rather than grow uncontrollably, so that the number of people needing medical care can be accommodated by available medical resources. You can search online for many excellent resources about this goal, termed “flattening the curve.”

How can each of us help?

Lowering contact rates is under your control, and this is the heart of “social distancing.” Interact with as few people as possible on a daily basis. By not gathering in classrooms, the library, or campus cafes, we are cutting a large portion of our daily contacts.  Each contact has some small probability of being the source of transmission of the virus to a new susceptible person. By avoiding contacts you do not give the virus an escape hatch to a new host individual.

Transmissibility is partly a feature of the virus and partly of immune systems. Do what you can to bolster your immune system and reduce the ways you get the virus into your system (hence advice to wash hands frequently, clean high-touch surfaces and not touch your face). 

Without a vaccine, we can’t change the susceptible fraction of the population.  That’s a while off. This means the virus will continue to circulate until we can reduce the susceptible fraction through a vaccine, or until very many people become infected with the virus, recover, have immunity (not clear yet if this occurs), and then have “herd immunity” based on there being very few people in the population.

The more people in the infected fraction, the higher the probability of new transmission.  Anyone feeling at all ill must stay home, be isolated, so that there is no opportunity for transmission. Mild symptoms must be managed at home to preserve hospital resources for the most ill and vulnerable.  

What is most worrisome for society, though potentially hopeful for individuals in our LC community, is that many people appear to have mild or no symptoms. Others suffer tremendously, though, and there are high death rates for some age groups. Mild cases also means there is a significant amount of transmission happening from individuals that otherwise feel healthy, as the most up-to-the-minute research is showing.  Just because you feel well, or don’t fall into a high-risk category, it is quite possible you could be transmitting the disease to others who are. Without sufficient testing, and our testing has been woefully inadequate, we just do not know how many infected individuals there are. Please take social distancing seriously and do all you can to isolate yourself from contacts outside your household. Do this to protect the vulnerable in our community, as well as to protect your own health.

Finally, use your voice.  Convince others that these practices are important too.  Read what the Italians are saying they wished they knew just weeks ago.  Let’s learn from other examples and join together to give the medical professionals a fighting chance. I have been so grateful to see how my students and colleagues have responded to the crisis. 

Margaret Metz

Assistant Professor of Biology

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