A Tale of Two Viruses: Why Smallpox was Eradicated and Polio Persists

The smallpox and poliomyelitis (polio) viruses were, at a time, one of the largest threats to global public health killing millions until global eradication campaigns were put into effect. Vaccination led to the eradication of smallpox and the elimination of polio for most of the world. However, polio continues to persist at endemic levels in Pakistan and Afghanistan. We developed ODE models of smallpox and polio to explore differences in transmission dynamics and determine if the underlying biology has made poliomyelitis more difficult to eradicate. Our model analysis shows there are multiple factors which should allow polio to have a lower threshold for eradication than smallpox: a lower threshold for herd immunity, and vaccines that are more effective at reducing infections and deaths. Thus, our model analysis leads us to conclude that the persistence of polio is due to the persistence of inadequate vaccination rates in the remaining polio-endemic countries

Modeling the Population Demographics & Viability of Imperiled Guzmania monostachia Populations

Guzmania monostachia is a large, long-lived bromeliad whose leaves grow in a rosette pattern and is native to the Americas, but endangered in Florida due to damage caused by the invasive weevil Metamasius callizona. Each G. monostachia rosette can reproduce sexually via flowers or asexually by producing clonal offshoot rosettes. We model the population dynamics and demographic structure of a G. monostachia population using a Lefkovitch matrix model where each state represents a demographic class of rosettes. Model analysis over a range of uncertain parameters show the conditions under which a G. monostachia population is viable in the absence and presence of M. callizona, and the expected demographic structure under those conditions. In particular, our analysis illustrates that proportional reductions in survival have a qualitatively stronger impact on population viability than proportion reductions in clonal fecundity