Hi John Vincent!

While there are many factors to the spread of disease, one ecological factor that stands out to me would be population size and density. For obvious reasons, the bigger and more closely-packed a group of animals are, the easier it is for a pathogen (ex: parasite) to spread among individuals. This scenario can happen in a forest due to deforestation because of edge effects. 

Edge effects are factors more prominent in the edges of an ecosystem (ex: forest). Edges of forests receive more wind and solar radiation. Additionally, they often experience more predation and human activity. These factors make edges a less ideal habitat versus the center. When forests are fragmented due to cutting, more edges are exposed and organisms are forced to move inward and away from them. Thus, size and density are increased along with the susceptibility to contract diseases.

Hello John Vincent!

I agree with Katrina, that among the factors that affect the spread of a disease is the population size, like in the case of parasites. In the simple equation for the number of infected hosts in parasitism (Rp), Rp = NBL (where N is the population, B is the transmission rate of disease, and L is the virulence of the disease), it is inferred that the greater populations have higher susceptibility to the disease since there are more hosts to infect.

On the genetic level, a more genetically diverse population has a higher chance of surviving an epidemic. Genetic diversity could act as a buffer in the spread of a disease. Aside from this, climate could also play a part in an epidemic as pathogens are known to thrive in warmer conditions. Hence, an increasing temperature will also increase disease in several hosts such as plants and humans.

Should you wish to find a more thorough discussion on these, you can find them here: https://www.nceas.ucsb.edu/science/disease#