The role of host density in the spread and outbreak of infectious disease

Transmission efficiency of many diseases is related to the density of the host populations. Lower host densities slow disease spread, and at a certain point host densities are insufficient to maintain infection. Considering that this theory forms the basis for vaccination and culling programs it is thus surprising that the existence of host density thresholds has rarely been experimentally verified. I use waterfleas (Daphnia) and their natural diseases to experimentally validate this theory and identify factors that facilitate or impede disease spread. Experimental results are integrated in mathematical models, which may help predict how global warming will affect disease spread and severity.