Why do we fear bioterrorism? Because diseases already emerge on their own into human populations with some success. A bioterrorist could make an emergence worse by causing it to happen more places at once than normal, with diseases we don't expect, with strains that are unusually virulent or treatment-resistant, or all of these at once.
The defense against bioterrorism is the same as a defense against natural disease outbreaks, but in greater depth.
Like all terror attacks, bioterrorism depends most of all on surprise. The best defense against any disease is to know how diseases operate in populations, and what lines of defense we have to stop them.
This is what Expedition 3 studied, so the entire site is of use when studying bioterrorism. Areas of particular interest:
A terrorist could evolve a disease strain with alarming characteristics, such as multidrug resistance.
Read about diseases that many regard as potential bioterror weapons:
a disease not usually