Answer:
Protein.
Step-by-step explanation:
Pathogens may be defined as the disease causing organism and capable of inducing immune response in the organisms. The organisms that can acts as pathogen are virus, bacteria and nematodes.
Different experiments have been performed to find the infectious agent. The digestion of trypsin protect the animals from the disease. This means the infectious agent must be protein as the protein digestion disrupts the pathogenicity of the organism.
Thus, the answer is protein.