Is there any description about how microbes spread from a small place to a very large place?

Birds migrate for thousands of miles, carrying diseases on a time scale of months or less. With climate shifts, insects and animals shift their ranges on a time scale of hundreds of years or more. Bacterial spores like anthrax can be in a form that is easily blown around the whole Earth, ready to thrive wherever they touch down. Plant diseases travel with their plant hosts, and over time scales of thousands of years the plants - e.g., dandelions and conifers - can spread thousands of miles of latitude and longitude.