Final answer:
The statement is true. Pathogens can cause disease when host defenses are compromised or when they enter non-natural parts of the body, especially if the immune system is weakened by chemotherapy or other factors.
Step-by-step explanation:
The subject of this question is Biology, particularly focusing on Pathogens and how they cause diseases. The statement presented is true; pathogens can cause disease in compromised hosts or if they grow in part of the body that is unnatural for them. The human body has many defense mechanisms that are highly beneficial to combat disease-causing organisms. However, when these defenses are weakened, for instance by chemotherapy or the presence of foreign objects like catheters, opportunistic pathogens may take advantage and cause infections.
Pathogens can enter the bloodstream through contaminated catheters or due to invasive procedures, creating a pathway for infection. The discriminated factor between primary and opportunistic pathogens is crucial; while primary pathogens can cause disease in a healthy individual, opportunistic pathogens primarily cause disease when the body's defenses are compromised.