April 21, 2016
Using their braaains, ASU researcher and colleagues use the undead to enliven the understanding of infectious-disease modeling
Ever since Bela Lugosi appeared in 1930s horror film “White Zombie,” members of the living dead have fascinated audiences.
Zombies have recently undergone a gruesome renaissance, with such television shows and films as “The Walking Dead,” “iZombie,” “World War Z,” “Pandemic” and “Pride and Prejudice with Zombies” presenting new twists on an old theme.
Now Reed Cartwright, a researcher at the Biodesign Institute, has brought zombie research to Arizona State University. The aim of his project, undertaken with colleagues from ASU, Washington State, Virginia Tech and Kent State University, is to use zombie epidemics to help health professionals, students and the general public gain a better understanding of mathematical modeling of infectious diseases and epidemiology.
“Zombies excite our brains as much as our brains excite zombies,” according to Cartwright, who is also an assistant professor in the School of Life Sciences. “By asking students to study zombie apocalypses, we hope to use familiar material to challenge students with difficult topics. At the end, they will be able to apply what they learn to biology, public health and epidemiology. Our students also learn that when a zombie outbreak occurs, there are two ways for humanity to survive: vaccination and extermination with extreme prejudice. Free hugs do not work.”
The spread of a communicable disease during an epidemic bears many similarities with the manner in which zombies would attack human communities. In each case, a virulent contagion is transmitted, giving rise to new carriers who in turn infect others, in a spreading wave of transmission.
The dynamics of such processes can be wildly complex and are best visualized and understood using sophisticated models in which various critical parameters — number of carriers, community size, rates of transmission, mortality figures, geographical landscape, etc. — can be modified and variant outcomes explored.
To this end, the group has created a simulation known as White Zed, a web-based application that can be used in classrooms to help students better understand and evaluate infectious-disease scenarios. A wide cultural familiarity with zombie epidemics makes them a highly useful analog for epidemics of real diseases affecting humans, providing an ideal learning tool.
Mathematical models of infectious diseases have provided science with invaluable insights into the dynamics of disease spread, recovery and, in some cases, reemergence. By representing conditions of an epidemic with a computer simulation, researchers can efficiently explore a variety of questions that might be impractical to examine in the course of an actual epidemic, due to financial, ethical, practical and other considerations.
In a recent paper appearing in the Journal of Microbiology and Biology Education, the authors describe how zombie epidemics have been incorporated into three introductory programs: a one-day workshop during a conference, a full-semester undergraduate course (taught by Cartwright), and a public outreach event.
“By asking students to study zombie apocalypses, we hope to use familiar material to challenge students with difficult topics."
— Reed Cartwright, ASU Biodesign Institute researcher
Long before the current explosion of zombie chic, these figures of the underworld appeared in ethnic folklore, particularly among voodoo practitioners in Haiti. Modern versions of zombies appearing in pop culture, however, have undergone a number of transformations. Unlike Haitian zombies, portrayed as the victims of spirit possession, zombies appearing in early films like “Night of the Living Dead” are deceased humans brought back to life.
Originally, these slow-moving zombies ambled around the countryside in search of their preferred meal: human flesh. More recently, fast-moving zombies have been introduced. These aggressive, violent creatures are not the classic reanimated dead, but rather, beings infected with some pathogen, variously described as a virus (“Walking Dead,” “World War Z,”), bacterium (“Deck Z,”), prion (“Zombieland”) or endo-parasitic fungus, such as those known to infect the nervous systems of insects, radically transforming their behavior (“The Last of Us”). Infection is commonly transmitted via bite, but can also be the result of water, bodily fluids or vectors. Times of incubation likewise vary widely.
Zombie models are in fashion!
As the authors note, the status of zombies in popular culture makes them an ideal vehicle for studying epidemiological issues and fundamentals of mathematical modeling. Using a fictional group like zombies encourages innovative thinking among students, rather than recourse to well-established concepts of transmission.
Instructors can use them to convey such principles as density-dependent transmission, frequency-dependent transmission, environmental transmission, latency periods, asymptomatic carriers, etc. The effects of various interventions — quarantine, culling, social distancing, etc. — can also be expored through advanced models.
First-author Eric Lofgren of Washington State University developed a one-day workshop, called “A Gentle Introduction to Mathematical Modeling: Real-life Lessons from the Living Dead.” The workshop was delivered to an audience of public-health professionals who may have had some familiarity with epidemiological models, but no hands-on experience with their design or analysis.
Each lecture featured one or more video clips highlighting specific concepts (for example, a segment from “Dawn of the Dead” bearing on incubation times). Subsequent discussion focused on models in the health literature, evaluating what assumptions given models used and what parameters were included.
The workshop progressed from a simple starting point in which a population is divided into S, Z and R categories, where S is susceptible, Z is zombie and R is removed. Later, more sophisticated models were explored in which survivors sought shelter or combatted their zombie attackers.
A hands-on portion of the workshop allowed students to independently implement two models: the basic zombie epidemic and a model extracted from the literature. So-called difference equation models enabled students to grasp many of the same insights provided by more challenging differential equation models, while only requiring high-school-level algebra.
“Zombies excite our brains as much as our brains excite zombies.”
A course in zombies
For those seeking the zombie total-immersion experience, Cartwright taught a class at Rice University on the biology of infectious diseases, which included a semester-long modeling project focusing on zombie invasions.
The class of 100 students was divided into five groups and tasked with assessing one of five zombie disasters. Students were asked to define the parameters of their models and design a mathematical model for zombie transmission. A subsequent draft refined the model and updated it to include natural birth and death of survivors as well as the hunting of zombies. In a final 15-page paper, students fitted their models to a data set provided by Cartwright and presented their results to the class.
Additional study materials for evaluating outbreaks were created by the Biocomplexity Institute of Virginia Tech in the form of a viral-transmission simulation activity known as Virus Tracker that includes visualization and analysis of an epidemic’s spread, highlighting the role of vaccination for thwarting viral disease outbreaks.
A more rigorous understanding of the fundamentals of mathematical disease modeling is important for students of biology, epidemiology and public health. A better appreciation of the use, interpretation and limitations of epidemiological models will help those in health-related fields more fully engage with medical literature and the multiple factors governing transmission events. As a carrier of contagion and cultural icon, zombies have much to teach us.
Top photo courtesy of www.cgpgrey.com [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons