2008 NSERC André Hamer Postgraduate Prize

Helen Alexander

If the term "zoonotic disease" leaves you a little fuzzy, perhaps "avian bird flu" can paint a clearer picture for you. Zoonosis refers to any pathogen which can travel from a vertebrate to a human. These pathogens are well-suited to their host animal, but when they make the transition to humans they often die out because of differences in immunity. In order to survive in their new hosts, the pathogens must undergo an evolutionary adaptation that arises through mutations, which can lead to a heightened ability to spread through human populations. In many cases, these pathogens do not achieve such a potent mutation and a small outbreak will occur in a concentrated area before the disease dies out. However, when a pathogen does make a successful adaptation, the potential for an epidemic emerges.

Mathematical biologist Helen Alexander has an interest in the probability of such an epidemic emerging in a population, but her answer is not restricted to the strength of a pathogen's adaptation. Instead, Alexander's master's research, for which she earned an André Hamer Postgraduate Prize, is focusing on the nature of human interactions to determine the probability of a zoonotic disease gaining a foothold to infect the masses if it is dependent on the interactions of populations.

Using a mathematical model, Alexander is constructing "contact networks" that recreate the interactions of a population. Previous work in this area has made the assumption that interactions occur randomly but, as anyone can attest, people tend to mingle in fairly predictable groups consisting of friends, family, coworkers, and so on. Such routine interactions, Alexander posits, would have considerable influence over the spread of an emerging disease.

To create a mathematical model of a disease is a difficult task on its own, but Alexander is attempting to devise as realistic a model as possible. To do this, she is using graph theory to simulate contact networks, with each vertex representing an individual and the connecting edges representing contacts between those individuals. She will also use randomizing components to simulate the probability of a disease's transmission from human to human, and the ways a pathogen mutation manifests itself.

Alexander's realistic model could help determine what measures should be taken to contain and control the spread of diseases. This, in turn, could give rise to changes in public policy about how cities and countries should react to avoid an epidemic taking hold of a population.

Previously, Alexander worked on a mathematical model for autoimmune diseases as her honor's thesis project. In 2007, she received an NSERC Undergraduate Student Research Award to fund summer research in mathematical biology at the University of Western Ontario. That same summer, she also attended the MITACS Industrial Summer Math School at Simon Fraser University, where she was part of a team that developed mathematical models of forest fires. She cites these experiences as having a major influence on her present work.