Biological attacks differ from chemical attacks in detection because:

Explanation

Most biological agents (anthrax, plague, smallpox, tularemia, viral hemorrhagic fevers, botulinum toxin) have incubation periods ranging from hours to several weeks, so unlike chemical attacks (where casualties often appear immediately), biological events frequently come to light through epidemiological surveillance — unusual clusters of disease, deaths exceeding expected patterns, or geographically unusual cases. Officers may, however, notice abandoned dispersal devices or letters with unknown powders. Most biological agents are not odorous/visible (a); they do affect humans (d); casualties may emerge gradually (b).